electronic supporting information ultrafast observation of
TRANSCRIPT
S1
Electronic Supporting Information
Ultrafast Observation of a Photoredox Reaction Mechanism: Photo-initiation
in Organocatalyzed Atom-Transfer Radical Polymerization
Daisuke Koyama, Harvey J. A. Dale and Andrew J. Orr-Ewing*
School of Chemistry, University of Bristol, Cantock’s Close, Bristol, BS8 1TS, United Kingdom
* Author for correspondence: [email protected]
Contents
Additional Analysis
PCF in DCM: Assigning 1PCF*(S1) vs
3PCF*(T1)
PCH and MBP in DMF: Complexation of 2PC
.+ and Br
-
Experimental
Ultrafast laser system
Transient vibrational absorption spectroscopy
Transient electronic absorption spectroscopy
Photocatalyst synthesis
Steady-state spectroscopy
Computational Methodology
Ground-state calculations
Excited-state calculations
Steady-State Spectroscopic Characterizations
FTIR spectra: PCF
Electronic spectra: PCF
S2
Spectroscopic characterization of 2PCF
.+(D1)
Spectroscopic characterization of 2PCH
.+(D1)
Computational Figures
Natural transition orbitals: PCF
Initial active space orbitals: PCF
Natural transition orbitals: PCH
Vertical transition energies: PCF
Vertical transition energies: PCH
Scaled harmonic frequencies
Reactivity of the debrominated radical 2MP
.(D1)
Transient Absorption Spectra
Example spectral decompositions
TEAS basis functions
Solvent effects: TEAS kinetic traces
Solvent effects: Semi-logarithmic plots of TEAS kinetic traces
Semi-logarithmic plots for TVAS measurements in DCM solutions
PCH and MBP in DCM: TVA spectra
PCF and MBP in DCM: TEAS concentration dependence
PCH: TEA spectra
Pure DCM: TEA spectra
Emission spectra: PCF with/without triplet quenchers
Triplet sensitization: PCF in DMF with benzophenone
S3
Additional Analysis
PCF in DCM: Assigning 1PCF*(S1) vs
3PCF*(T1)
Transient electronic absorption spectra of PCF in DCM following pulsed photoexcitation at 370 nm are
shown in Figure S1. Mechanistic insight into the photophysical relaxation pathway may be garnered from
the early-time kinetic regime (0 – 5 ps). Global fitting of time-dependent integrated band intensities to a
simple A →B (τ1) mechanism, convoluted with an instrument response function of 120 fs, affords a time
constant τ1 = 230 ± 30 fs.
The transient species B is fully formed within 2 ps and metastable on the timescale 2 – 100 ps, but decays
by 30% over 100 – 1200 ps (Figure S2). The time constant for the decay is beyond the range of our
experiment but is estimated to be 3 ± 1 ns.
Figure S1: Ultrafast photophysical relaxation of PCF in DCM. Transient electronic absorption spectra of PCF
(2.1 mmol dm-3
) in DCM are shown for the first 5 ps after photoexcitation at 370 nm, alongside kinetic traces for
1PCF*(Sn) (○) and
1PCF*(S1)(○). The lines show the result of global fitting to a mechanism
1PCF*(Sn) →
1PCF*(S1), convoluted with an instrument response function of 120 ps. Spectral decompositions for example time
slices are shown in Figure S11. Transient signal from pure DCM is negligible under the same conditions and
over the same probe region (see Figure S21).
We assign A as the nascent excited electronic state of the photocatalyst 1PCF*(S4), or transiently
populated S3 or S2 states, and the long-lived state B as the first excited singlet state 1PCF*(S1). The only
alternative electronic state that might plausibly have a lifetime consistent with B is 3PCF*(T1), but such an
assignment was discounted for the following reasons: (i) if intersystem crossing (ISC) from the singlet
manifold to 3PCF*(T1) were to occur with a time constant of hundreds of femtoseconds, the steady-state
emission would be dominated by phosphorescence, rather than fluorescence; (ii) there is no compelling
1PCF*(S1)
1PCF*(Sｎ (n = 2 - 4))
400 450 500 550 6000
5
10
15
Time / ps
0.0
0.3
0.7
1.5
2.5
4.0
Absorbance / m
OD
Wavelength / nm
-1 0 1 2 3 4 5
0.0
0.2
0.4
0.6
0.8
1.0
Integrated intensity
Time / ps
S4
theoretical explanation for such a fast ISC in this structurally rigid molecule, composed exclusively of
first-row main group elements; and (iii) the decay time constant of B (3 ±1 ns) is far shorter than is often
observed for phosphorescence or ISC from the first excited triplet state to the ground state of organic
molecules. Assigning the metastable state B to 3PCF*(T1) would therefore require two abnormally fast
ISCs – one from a high-lying singlet state into the triplet manifold, and a second from 3PCF*(T1) to the
ground state 1PCF(S0). Moreover, none of the triplet quenchers Q considered in the steady-state
experiments (2,5-dimethyl-hexa-2,4-diene, cyclohexa-1,3-diene, styrene) had any effect on the decay
kinetics of B on our timescale, even when present in vast excess ([Q] ~1 mol dm-3
).
Although global fitting to a sequential mechanism A →B → C proved intractable, the presence of at least
two independent absorption features between 400 – 500 nm is supported by the asymmetric spectral
profile in this region, which undergoes a concerted narrowing and red-shift over the first few picoseconds.
This, and the shifting isosbestic point over 500 – 510 nm, suggest the involvement of an intermediate
singlet state and therefore a stepwise, rather than concerted, descent from 1PCF*(S4) to
1PCF*(S1) via
sequential internal conversions.
The transient vibrational absorption spectra of PCF over 1280 – 1380 cm-1
(Figure S2) depict vibrational
signatures of 1PCF*(S1) and the ground-state
1PCF(S0), corresponding to fundamental transitions in ring-
breathing modes. The early-time spectra are characteristic of vibrational relaxation, and the temporal
evolution of the integrated band intensities affords a time constant of 15 ± 2 ps.
S5
Figure S2: Photophysical dynamics of PCF in DCM following pulsed photoexcitation at 370 nm. (a) TVA
spectra showing vibrational cooling of the 1PCF*(S1) state, decay of
1PC*(S1) and recovery of the ground-state
1PCF(S0). Inset: time-dependence of the
1PCF*(S1) band position, affording a time constant of (15 ± 2 ps) for
vibrational relaxation; (b) kinetic traces for depletion of 1PCF*(S1) (black) and recoveries for the
1PCF(S0) bands
at 1324 cm-1
(blue) and 1345 cm-1
(red); (c) TEA spectra of the same system, showing the decay of the 1PCF*(S1)
state over the period 10 – 1200 ps; (d) kinetic trace of 1PCF*(S1), as obtained from (c) via the time-dependent
integration of the fitted band. Crucially, the total decay of the 1PCF*(S1) state (30 % over 30 – 1200 ps) is
matched by the fractional recovery of the ground-state; this correspondence suggests that the ISC quantum yield
is imperceptibly low.
The depletion of A and growth of B occur with a time constant (230 ± 30 fs) an order of magnitude
smaller than that found for the vibrational relaxation (15 ± 2 ps) of the 1PCF*(S1) state, suggesting that
the red-shift of the spectra over 400 – 500 nm cannot correspond to vibrationally hot 1PCF*(S1). Solvent
reorganization following a direct internal conversion from 1PCF*(S4) to
1PCF*(S1) might lead to early-
time shifts in the excited state absorptions, but the anticipated stabilization of the 1PCF*(S1) state due to
1300 1320 1340 1360 1380 1400
-20
-10
0
10
20
30Absorbance / m
OD
Wavenumber / cm-1
Time / ps
1
15
50
200
500
(c) TEAS (d)
1PCF*(S1)
1PCF(S0): 1345 cm-1
1PCF(S0): 1324 cm-1
1PCF*(S1)
1PCF*(S1)
(a) TVAS (b)
PCF(S0)
1PCF*(S1)
0 20 40 60 80 1001304
1306
1308
1310
Band position / cm
-1
Time / ps
200 400 600 800 1000 1200
-0.6
-0.4
-0.2
0.6
0.8
1.0
Integrated signal
Time / ps
400 450 500 550 6000
5
10
15
Absorbance / m
OD
Wavelength / nm
Time / ps
10
100
500
800
1200
200 400 600 800 1000 12000.0
0.2
0.4
0.6
0.8
1.0
Integrated signal
Time / ps
S6
its CT character should cause a progressive blue-shift, rather than the observed red-shift, of the transient
electronic spectra over the first few ps.
Critically, the total decay amplitude of the excited singlet state over 100 – 1200 ps corresponds closely to
the fractional recovery of the ground-state bleach, suggesting that fluorescence and internal conversion –
but not intersystem crossing – are efficient relaxation pathways for 1PCF*(S1). The formation of
3PCF*(T1) would also afford a distinct transient absorption growing over time, but no such band was
observed in any region. This evidence suggests that the ISC quantum yield is imperceptibly low, and that
a substantial majority of 1PCF*(S1) returns to the ground-state within several nanoseconds, in agreement
with the assignment of 1PCF*(S1) from the TEA spectra above (Figure 1).
PCH and MBP in DMF: Complexation of 2PC
.+ and Br
-
In DMF solution there is a component in the transient electronic spectrum of PCH + MBP centered on
470 nm (Figure 4), which continues to grow significantly after 1PCH*(S1) is depleted. As
1PCH*(S1) is
almost fully depleted within 100 ps this feature cannot correspond to intersystem crossing to 1PCH*(T1),
nor can it correspond to a PET from 3PCH*(T1), as the population of the
2MP
.(D1) radical reaches a
plateau after 100 ps. We attribute this subtle change in the absorption signature of the radical cation
2PCH
.+(D1) to complexation with bromide to form the radical ion pair
2PCH
.+Br
-.
S7
Experimental
Ultrafast Laser System
Details of the ultrafast laser system and experimental procedure are summarised in the Methods section of
the main paper and elsewhere.1
Transient Vibrational Absorption Spectroscopy (TVAS)
For all TVAS experiments the carrier wavelength of the UV pump pulse was set to 370 nm and the IR
probe pulses were characterised by a bandwidth of approximately 250 cm-1
. The UV pump pulses emitted
from the OPA were attenuated by cross-polarization to afford pulses of energy 600 nJ at the sample. The
UV pump and IR probe pulses were configured to intersect each other at the sample at a small angle of 5°,
and precisely controlled time delays τ between the pump and probe pulses were attained with an
aluminium retro-reflector mounted on an adjustable mechanical delay stage of length 220 mm (Thorlabs
DD5220/M). This corresponds to a maximum temporal delay of 1.3 ns. Difference absorption spectra
∆A(ν, τ) were obtained by placing a revolving chopper wheel along the UV pump beamline, with an
angular frequency of 500 Hz and a phase adjusted to block alternate pump pulses. Prior to interacting with
the sample, the IR probe beam was split into two beams of identical energy: (i) one beam was transmitted
through the sample and directed onto a Mercury Telluride Cadmium array (Infrared Associates Inc.,
MCT-10-128) mounted within an infrared spectrometer (Horiba Scientific, iHR320, 2 cm-1
pixel-1
); and
(ii) the second beam was directed straight into an identical detector and spectrometer, without passing
through the sample. Comparison of the two recorded signals accounted for fluctuations between
successive pulses, thereby reducing artificial differences between individual transient spectra recorded for
any given time delay. Systematic drifts in the signal intensity over the timescale of the experiment can
lead to the emergence of misleading kinetics; to avoid this possibility, transient spectra were recorded in a
randomized – as opposed to ascending or descending – sequence of time delays. To minimise absorption
of the infrared probe by ambient water vapor, the beamline was partially enclosed and purged with dry
nitrogen.
Transient Electronic Absorption Spectroscopy (TEAS)
For TEAS a broadband white light supercontinuum was used to probe the wavelength region 330–630
nm, following photoexcitation with a pump pulse of carrier wavelength 370 nm. The supercontinuum
S8
probe pulses were generated by focussing the parent 100 �J pulse beam onto a CaF2 window of 2mm
thickness with a CaF2 lens of focal length 200 mm; to prevent thermal degradation of the window a cross-
polariser and series of neutral density filters were used to attenuate the parent beam intensity and the
window was continuously rastered in the plane perpendicular the incident beam direction. The
polarization of the supercontinuum probe was shifted relative to the UV pump pulse by the magic angle
(54.7°), and the two beams were configured to intersect at the sample at an angle of 5°. Difference
absorption spectra were obtained by placing a revolving chopper wheel along the UV pump beamline,
with an angular frequency of 500 Hz and a phase adjusted to block alternate pump pulses. The transmitted
probe pulses were collected by an optical fibre coupled to a CCD spectrometer (Avantes, AvaSpec-
DUAL), affording a spectral resolution of 0.6 nm pixel-1
.
Photocatalyst Synthesis2
5,10-dihydrophenazine 1
A conical flask was charged with phenazine (2.0 g, 11 mmol) in EtOH (50 mL) and heated to reflux. With
stirring, a solution of Na2S2O4 (23.3 g, 134 mmol) in 200 mL of distilled water was then added over a
period of 5 min, leading to the formation of a pale green precipitate after 10 min. The crude solid was
isolated via vacuum filtration, washed thoroughly with distilled water and dried in vacuo to afford 5,10-
dihydrophenazine (1) as a pale green powder (1.75 g, 9.6 mmol, 87 %). The photocatalysts PCF (2) and
PCH (3) were synthesised immediately after exposing 1 to the atmosphere.
5,10-di(4-trifluoromethylphenyl)-5,10-dihydrophenazine (PCF) 2
The photocatalyst PCF (2) was synthesised via a Buchwald-Hartwig coupling reaction. An oven-dried
round-bottom flask was charged with a magnetic stirrer bar, 1 (0.50 g, 2.7 mmol), NaOtBu (1.0 g, 10.4
mmol), RuPhos (50 mg, 0.11 mmol), RuPhos precatalyst (90mg, 0.11 mmol), para-
bromobenzotrifluoride (2.5 g, 11 mmol) and 1,4-dioxane (6 ml) and heated to 100 °C under an
atmosphere of nitrogen. After 10 hr the crude yellow solid was isolated via vacuum filtration, dissolved in
Na2S2O4
EtOH / H2O
1
S9
a minimal quantity of DCM and then crystallised with the addition of n-hexane to afford 2 as a yellow
solid (0.96 g, 2.0 mmol, 76 %). Further crystallization from toluene solution gave yellow crystals. The
crystal was stored below 5°C. Characterization was confirmed by comparison the previously reported
values. δ1H / ppm (toluene-d8, 400 MHz) = 7.37 (d, J = 8.0 Hz, 4H), 6.97 (unable to resolve from the
toluene-d8 peak), 6.31 (m, 4H), 5.65 (m 4H). HRMS (ESI) M+ m/z = 470.1218 (Calc.), 470.1220 (Meas.).
UV-Vis �max (DCM) = 370 nm.
5,10-diphenyl-5,10-dihydrophenazine (PCH) 3
The photocatalyst PCH (3) was synthesised in a similar manner to the synthesis of 2. An oven-dried
round-bottom flask was charged with a magnetic stirrer bar, 1 (0.50 g, 2.7 mmol), NaOtBu (1.0 g, 10.4
mmol), RuPhos (50 mg, 0.11 mmol), RuPhos precatalyst (90mg, 0.11 mmol), para-bromobenzene (1.7 g,
11 mmol) and 1,4-dioxane (6 mL). The solution was heated to 100 °C under an atmosphere of nitrogen
and stirred for 10 hr. After cooling to room temperature, 100 mL of DCM was added to the reaction
solution, and the solution washed with 100 mL of distilled water three times. The organic layer was
collected and concentrated to ~5 mL in vacuo, causing precipitation of a yellow powder that was then
collected via vacuum filtration. This purification procedure was repeated once more, giving 3 as yellow
powder (0.75 g, 2.2 mmol, 83%). Recrystallization from toluene / methanol solution gave yellow needles,
which were stored below 5°C. Characterization was confirmed by comparison to previously reported
values. δ1H / ppm (toluene-d8, 400 MHz) = 7.20 (t, J = 7.6 Hz, 4H), 7.13 (unable to resolve from toluene-
d8 peak), 7.07 (m, 2H), 6.24 (m, 4H), 5.75 (m, 4H). HRMS (ESI) M+ m/z = 334.1470 (Calc.), 334.1474
(Meas.).
+
RuPhosRuPhos Precat.
NatOBu
1,4-dioxane
1
2
S10
Steady-State Spectroscopy
All steady-state UV-Vis absorption spectra reported herein were obtained with a Thermo Scientific
Genesys 10S spectrophotometer. Emission spectra were measured with a Varian Cary Eclipse
spectrophotometer using 10 nm excitation and 20 nm emission slits. Solutions were prepared to a
concentration such that they exhibited a maximum absorbance of 0.05 < A(�max) < 0.1 at the excitation
wavelength �max. Both electronic absorption spectra and emission spectra were obtained using glass
cuvettes of path length 1 cm. FTIR spectra were recorded on a Perkin Elmer Spectrum-Two spectrometer,
with solutions contained in a stainless steel Harrick cell with CaF2 windows and sample path length of 50
�m.
Computational Methodology
Ground-State Calculations
Restricted Kohn-Sham density functional theory (RKS-DFT) was employed to investigate the geometries
and harmonic vibrational frequencies of pertinent closed-shell species in their ground electronic state (S0).
Geometries and frequencies of open shell species in their ground doublet state (D1) were obtained within
the unrestricted formalism (UKS-DFT). All KS-DFT calculations were run with the Gaussian09 suite of
programs and a fine numerical integration grid at T = 298.15 K.3
Ground-state geometry optimizations and harmonic vibrational frequency calculations were conducted
with the pure hybrid-GGA functional PBE0 and a polarised and augmented double-zeta basis set 6-
31+G(d) (6d,7f).4 All optimizations were initiated from highly distorted structures devoid of any
symmetry elements. Equilibrium solvation effects were included by implicitly simulating the solvent as a
continuous polarisable medium with the total solute density model (SMD) of Truhlar et al.,5-7
and in the
case of the PBE0 functional long-range London dispersion interactions were simulated with Grimme’s D3
RuPhosRuPhos Precat.
NatOBu
1,4-dioxane+
1
3
S11
dispersion correction, supplemented by the Becke-Johnson damping function (GD3BJ).8 The eigenvalues
of the Hessian matrix were checked for each species to confirm its presence at a genuine minimum or
saddle-point (TS) on the potential energy surface. Linear scaling factors for harmonic vibrational
frequencies and associated uncertainties were obtained by comparison to experimental steady-state FTIR
spectra. Predicted vibrational frequencies of the transient species 3PCF*(T1),
2PCF
.+(D1),
2PCF
.-(D1),
2MP
.(D1),
2PCF
.+Br
- and {
1PCF(S0), Br2} were obtained by computing their harmonic frequencies and
adjusting with the scaling factor obtained from this comparison. To enable direct comparison with excited
states (below), molecular electrostatic potentials (MEPs) were computed at the CAM-B3LYP/6-
31+G(d)/SCRF=(SMD, DCM) level of theory.9 Accurate ground-state potential energies were obtained
with unrestricted KS-DFT, unless explicitly stated otherwise, with single-point calculations at the
B2PLYPD3/6-311++G(2d,p)/SCRF=(SMD,DCM)//PBE0-GD3BJ/6-31+G(d)/SCRF=(SMD,DCM) level
of theory.9 The corresponding Gibbs free energies were computed by including the thermal correction
from the optimization level of theory.
The Gibbs free energy change for the PET ∆PETG, C – Br bond dissociation energy of MBP EBD and
Gibbs free activation barrier ∆PETG‡ were computed for each photocatalyst according to the equations
below. All ground-state free energies were computed at the B2PLYPD3/6-311++G(2d,p)/SCRF=(SMD,
DCM)//PBE0-GD3BJ/6-31+G(d)/SCRF=(SMD, DCM) level of theory at 298 K. The energy of the
excited singlet state [1PCF*(S1) or
1PCH*(S1)] in each case was estimated from the wavelength of
maximum emission. This method neglects the Coulombic term present in the Weller equation and the
solvent reorganization energy in the Marcus equation, but these are reasonable first-approximations for a
dissociative ET in which the excited state energy and bond dissociation energy are the dominant terms.
Δ�� ≈ ����.�� + ����.� + ������� − ����� + ������ + ��,�� ����MBP� ≈ ����.� + ����.�� − ������� = 210kJmol*+
Δ��‡ ≈���4 .1 + Δ����� /0
KS-DFT computations predict a C – Br bond dissociation energy of EBD[MBP] = 210 kJ mol-1
for the
initiator. The intrinsic rate coefficient for the electron transfer may be calculated according to the equation
below, where κel is the electronic transmission coefficient, νn is the nuclear vibration frequency related to
the electron transfer and κelνn ~ 1012
dm3 mol
-1 s
-1.10
1234 = 56789 exp =−Δ��‡
>? @
S12
Photocatalyst AB,B/
(kJ mol-1
) {nm}
CDEFG / (kJ mol
-1)
CDEFG‡ / (kJ mol
-1)
HIAJ / (dm
3 mol
-1 s
-1)
PCF 213 {562} -95 16 1.6 × 109
PCH 249 {480} -145 5 1.3 × 1011
Although this is an approximate computation of rate coefficients, agreement with experiment is good.
Some degree of fortuitous error cancellation may play a role, but it is notable that the calculation captures
the essential conclusions of our experimental work: (i) PET from 1PCH*(S1) to MBP will be limited by
diffusion; and (ii) PET from 1PCF*(S1) is slower than from
1PCH*(S1), and activation controlled, with a
bimolecular rate coefficient of the order 109 dm
3 mol
-1 s
-1.
Excited-State Calculations
Vertical transition energies, oscillator strengths and excitation amplitudes were computed with time-
dependent density functional theory (TD-DFT) and the second-order perturbation-corrected configuration
interaction singles method (CIS(D)) in Gaussian09.11-13
For TD-DFT calculations a selection of global
hybrid-GGA and range-separated exchange-correlation functionals (EX-C) – including CAM-B3LYP,
wB97XD, LC-wPBE, PBE0, M06-2X, B3LYP and B98 – were used in conjunction with the 6-
311++G(2d,p) (5d, 7f) basis set and non-equilibrium SMD solvation to characterise the excited electronic
states of the photocatalyst in the Franck-Condon region. The Coulomb-attenuated variant of the B3LYP
functional (CAM-B3LYP) has been reported to provide satisfactory description of delocalised π-π*
excited states in organic dyes and of charge-transfer excitations generally,14-16
and this was corroborated
herein by comparison to the steady-state UV-vis spectrum of the photocatalyst. More expansive basis sets,
ranging up to the minimally-augmented triple-zeta correlation-consistent basis set from Dunning and co-
workers (spaug-cc-PVTZ), had a negligible effect on computed vertical transition energies and oscillator
strengths. Natural transition orbitals (NTOs) and simulated UV-vis spectra were thus computed at the
CAM-B3LYP/6-311++g(2d,p)/SCRF=(SMD,DCM,NonEq))//PBE0+GD3BJ/6-
31+G(d)/SCRF=(SMD,DCM) level of theory.
State-averaged complete active space self-consistent field (SA-CASSCF) calculations were pursued to
accurately characterise the vertical electronic transitions of the photocatalyst from an ab initio
perspective. All SA-CASSCF calculations were conducted in vacuo with the 6-311G(d,p) basis set using
the Molpro package (v2010.1).17-19
The input geometries was obtained by imposing C2h and D2h
S13
symmetries on the ground-state photocatalysts PCF and PCH, respectively, and reoptimising in
Gaussian09 at the PBE0+GD3BJ/6-31+G(d)/SCRF=(SMD,DCM) level of theory; with the exception of
minor rotations in the trifluoromethyl substituents, the resulting structures were essentially isoenergetic
relative to the fully relaxed species. As such, the trifluoromethyl substituents were treated as free rotors.
Initial canonical molecular orbitals were obtained from a restricted Hartree-Fock single-point calculation
with the 6-311G(d,p) basis set, from which a benchmark active space of 14 electrons in 14 orbitals was
constructed (14,14); the active orbitals comprised the seven highest occupied π orbitals and seven lowest
unoccupied π* orbitals. A second, more compact active space (8,8), including only those occupied π
orbitals localised exclusively on the central phenazine moiety and virtual π* orbitals confined primarily to
the trifluoromethylphenyl substituents, was also examined, alongside an intermediate-sized active space
(10,10). Unless explicitly stated otherwise, the optimised SA-CASSCF orbitals were obtained by
minimising the average energy of: (i) the ground electronic state (Ag) and the first excited state of each
symmetry species (Ag, Au, Bu, Bg) for PCF (C2h); and (ii) the ground electronic state (Ag) and the first four
lowest singlet states (B1g, B2u, Au, B3g) for PCH (D2h). In both cases, each of the five states was afforded
an equal weighting in state-averaging.
Accurate vertical transition energies were obtained using internally-contracted second-order
multireference perturbation theory (CASPT2) and adjusted by -0.1 eV to account for basis-set
incompleteness, in accordance with the benchmarking work of Thiel and co-workers.20
The SA-CASSCF
result was used as a reference wavefunction for the CASPT2 calculation and a small imaginary level shift
of 0.1 Eh was employed to circumvent intruder state problems. Transition dipole moments were obtained
from the SA-CASSCF wavefunctions.
Optimised geometries and molecular electrostatic potentials (MEPs) of excited singlet states were
obtained with TD-DFT at the CAM-B3LYP/6-31+G(d)/SCRF=(SMD,DCM) level of theory.21
S14
Steady-State Spectroscopy
FTIR spectra: PCF
Figure S3: Assorted FTIR spectra for PCF with solvent absorption subtracted: (a) MBP (0.18 mol dm-3
) in
toluene-d8; (b) PCF (5.3 mmol dm-3
) in toluene-d8; (c) PCF (5.3 mmol dm-3
) and MBP (0.18 mol dm-3
) in toluene-
d8; (d) difference spectrum (c) – (a). The absence of additional vibrational absorptions for the PCF + MBP system
– and therefore the equivalence of (b) and (d) – discounts the formation of a donor-acceptor complex in the
ground-state.
0.0
0.1
0.2
Absorbance
0.0
0.1
0.2
Absorbance
0.00
0.05
0.10
1400 1450 1500 1550 1600 1650 1700
0.00
0.05
0.10
Wavenumber / cm-1
(a) MBP
(b) PCF
(c) MBP + PC
(d) spectrum (c) – (a)
Absorbance
S15
Electronic Spectra: PCF
Figure S4: Assorted electronic spectra for PCF. (a) UV-vis absorption spectra for PCF in acetonitrile (∎),
toluene (∎), ethanol (∎), DCM (∎) and DMF (∎); (b) emission spectra for PCF in acetonitrile (∎), toluene (∎),
ethanol (∎), DCM (∎) and DMF (∎) following excitation at 370 nm; (c) excitation spectrum of PCF in DCM for
emission at 570 nm.
300 350 400 450 500
0.0
0.5
1.0
Norm
alized absorbance
Wavelength / nm
DCM
EtOH
MeCN
toluene
DMF
450 500 550 600 650 700
0.0
0.5
1.0
Norm
alized intensity
Wavelength / nm
DCM
EtOH
MeCN
toluene
DMF
300 350 400 450 500
0.0
0.5
1.0
Norm
alized intensity
Wavelength / nm
(b) Emission
(c) Excitation
(a) UV-vis
S16
Spectroscopic Characterization of 2PCF
.+(D1)
Figure S5: Steady-state spectroscopic characterization of the radical cation 2PCF
.+(D1), following thermally-
mediated oxidation of PCF with FeCl3. (a) UV-vis absorption spectra of PCF in DCM following the addition of n
equivalents of FeCl3; (b) FTIR spectra of PCF in DCM following the addition of n equivalents of FeCl3. The
emergence of a vibrational absorption at 1553 cm-1
confirms the assignment of 2PCF
.+(D1) in the transient spectra
presented in Figure 1(c).
Spectroscopic Characterization of 2PCH
.+(D1)
Figure S6: Steady-state spectroscopic characterization of the radical cation 2PCH
.+(D1) following thermally-
mediated oxidation of PCH with FeCl3. (a) UV-vis absorption spectra of PCH in DCM following the addition of
n equivalents of FeCl3; (b) FTIR spectra of PCH in DCM following the addition of n equivalents of FeCl3.
1480 1500 1520 1540 1560 1580
0.00
0.05
0.10
0.15
Wavenumber / cm-1
0 eq
0.5 eq
1.0 eq
2.0 eq
3.0 eq
(a) UV-vis (b) FT-IR
2PCF・+(D1)
2PCF・+(D1)
1PCF(S0)
400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
Absorbance
Wavelength / nm
0 eq
0.5 eq
1.0 eq
1.5 eq
2.0 eq
2.5 eq
1540 1550 1560
1480 1500 1520 1540 1560 1580
0.00
0.05
0.10
0.15
Absorbance
Wavenumber / cm-1
0 eq
0.5 eq
1.0 eq
2.0 eq
3.0 eq
(a) UV-vis (b) FT-IR
2PCH・+(D1)
2PCH・+(D1)
1PCH(S0)
400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0
Absorbance
Wavelength / nm
0 eq
0.5 eq
1.0 eq
1.5 eq
2.0 eq
2.5 eq
1540 1550 1560
S17
Computational Figures
Natural Transition Orbitals: PCF
CAM-B3LYP/6-311++G(2d,p)/SCRF=(SMD,DCM)//PBE0-GD3BJ/6-31+G(d)/ SCRF=(SMD,DCM)
Figure S7: Natural transition orbitals for vertical electronic transitions of PCF to the first four excited singlet
states, computed at the CAM-B3LYP/6-311++G(2d,p)/SMD(DCM)//PBE0-GD3BJ/6-31+G(d)/SMD(DCM) level
of theory. The symmetry of PCF was constrained to the C2h point group.
S18
Initial Active Space Orbitals (SA-CASSCF): PCF
HF/6-311G(d,p)
Figure S8: Canonical molecular orbitals for PCF, computed at the HF/6-311G(d,p)//PBE0-GD3BJ/6-
31+G(d)/SMD(DCM) level of theory, with the system constrained to the C2h point group. These orbitals were
used for subsequent SA-CASSCF/CASPT2 computations, as outlined in the computational methodology section.
The PCH canonical MOs, computed at the same level of theory under D2h symmetry, were very similar to those
for PCF, with minor re-orderings.
S19
Natural Transition Orbitals: PCH
CAM-B3LYP/6-311++G(2d,p)/SCRF=(SMD,DCM)//CAM-B3LYP/6-31+G(d)/ SCRF=(SMD,DCM)
Figure S9: Natural transition orbitals for vertical electronic transitions of PCH to the first four excited singlet
states, computed at the CAM-B3LYP/6-311++G(2d,p)/SMD(DCM)//PBE0-GD3BJ/6-31+G(d)/SMD(DCM) level
of theory. The symmetry of PCH was constrained to the D2h point group.
S20
Vertical Transition Wavelengths (nm): PCF
Table S1: Vertical transition wavelengths (nm), state-symmetries and oscillator strengths/transition dipole moments
computed for PCF under the C2h point group with TD-DFT (CAM-B3LYP,M06-2X,PBE0-GD3BJ/6-
311++G(2d,p)/SMD(DCM)//PBE0-GD3BJ/6-31+G(d)/SMD(DCM)) and SA-CASSCF/CASPT2 (6-311G(d,p);
CAS(14/14), CAS(8/8)). Oscillator strengths (f) are shown for TD-DFT; transition dipole moments (Debye) are
shown for the SA-CASSCF transitions.
Vertical Transition Wavelengths (nm): PCH
State CAM-B3LYP CAS(14/14)/CASPT2 CAS(8/8)/CASPT2
S1 376 (B1g) 0.00 361 (B1g) 0.00 376 (B1g) 0.00
S2 333 (B2u) 0.206 342(B2u) 4.40 353 (B2u) 4.40
S3 317 (Au) 0.00 310 (Au) 0.00 334 (Au) 0.00
S4 314 (B3g) 0.00 305 (B3g) 0.00 327 (B3g) 0.00
Table S2: Vertical transition wavelengths (nm), state-symmetries and oscillator strengths/transition dipole moments
computed for PCH under the D2h point group with TD-DFT (CAM-B3LYP/6-311++G(2d,p)/SMD(DCM)//PBE0-
GD3BJ/6-31+G(d)/SMD(DCM)) and SA-CASSCF/CASPT2 (6-311G(d,p); CAS(14/14), CAS(8/8)). Oscillator
strengths (f) are shown for TD-DFT; transition dipole moments (Debye) are shown for the SA-CASSCF transitions.
State CAM-B3LYP M06-2X PBE0 CAS(14/14)/
CASPT2
CAS(8/8)/
CASPT2
S1 374 (Ag) 0.00 379 (Ag) 0.00 448 (Au) 0.00 374 (Au) 0.00 380 (Au) 0.00
S2 355 (Au) 0.00 364 (Au) 0.00 443 (Bg) 0.00 366 (Bg) 0.00 376 (Ag) 0.00
S3 352 (Bg) 0.00 360 (Bg) 0.00 418 (Ag) 0.00 362 (Ag) 0.00 374 (Bg) 0.00
S4 337 (Bu) (0.154) 341 (Bu) (0.131) 399 (Bu) (0.042) 353 (Bu) 1.90 371 (Bu) 4.20
S21
Scaled Harmonic Frequencies
Transient species Predicted vibrational absorptions / cm-1
1PCF(S0)
1601 (306), 1477 (1494), 1352 (499), 1337 (478)
2PCF
.+(D1) 1603 (160), 1551 (243), 1333 (232)
2MP
.(D1) 1659 (357)
Table S3: Key vibrational absorption frequencies (cm-1
) and corresponding intensities (bracketed) for the ground-
state 1PCF(S0), radical cation
2PCF
.+(D1), and the
2MP
.(D1) radical, computed at the PBE0-GD3BJ/6-
31+G(d)/SMD(DCM) level. The wavenumber values were linearly scaled by a factor of fs = 0.957 ±0.0016 and
used to help assign 2PCF
.+(D1) and
2MP
.(D1) in Figure 1.
S22
Reactivity of Debrominated Radical 2MP
.(D1)
B2PLYPD3/6-311++G(2d,p)/SCRF=(SMD,DCM)//PBE0-GD3BJ/6-31+G(d)/ SCRF=(SMD,DCM)
Figure S10: Optimised transition state structures and free energies of activation ∆G‡ for five possible decay
mechanisms of the radical 2MP
.(D1), including: (a) H-atom abstraction from DCM; (b) Cl-atom abstraction from
DCM; (c) H-atom abstraction from MBP; (d) Br-atom abstraction from MBP; and (e) radical addition to the
terminal carbon of methyl methacrylate (MMA). Optimised geometries and thermodynamic corrections were
obtained at the PBE0-GD3BJ/6-31+G(d)/SCRF=(SMD,DCM) level of theory; single-point potential energies
were then computed at the B2PLYPD3/6-311++G(2d,p)/SCRF=(SMD,DCM) level, using the previously
optimised structures. All abstraction reactions have free energies of activation in excess of 80 kJ mol-1
, suggesting
that the radical will be metastable on the picosecond timescale (as observed). Although the reaction of 2MP
.(D1)
with MMA is known to be facile under ambient conditions, no reaction was observed on our timescale; this is
consistent with the computed free energy of activation (52 kJ mol-1
), as for activation-controlled reactions to be
observable on our timescale the barrier should be less than ~ 25 kJ mol-1
.
S23
Transient Absorption Spectra
Example Spectral Decompositions
Transient electronic and vibrational spectra were decomposed into constituent parts using the KOALA
program,22
or Origin9 software to identify transient gain features and obtain kinetic traces. Examples of
spectral decompositions are provided in Figure S11 for TEA spectra of PCF in DCM solution (Figure
S1), in Figure S12 for TVA spectra of PCF / MBP in DCM solution (Figure 1(c)), and in Figure S13 for
TEA spectra of PCH or PCF / MBP in DCM solution (Figure 4).
Figure S11: Decompositions of TEA spectra for PCF (2.1 mmol dm-3
) in DCM (Figure S1) at 0.1 ps, 0.2 ps, 0.3
ps, 0.5 ps and 1.0 ps. The fitting residuals at around 430 nm indicate the intermediate electronic states, vibrational
relaxation, or solvation dynamics mentioned in main article. The two basis functions for the decomposition are
shown in the top panel.
0
5
10
15
0
5
10
15
400 450 500 550 600
0
5
10
15
Wavelength / nm
0
5
10
15
Absorbance / m
OD
0
5
10
15
0
5
10
15
TEA spectra
0.1 ps
0.2 ps
0.3 ps
0.5 ps
1.0 ps
5.0 ps0.0 ps
1PCF*(Sn)
TEA spectrum
Total fitting
1PCF*(S1)
10
15
Absorbance / mOD
S24
Figure S12: Decompositions of TVA spectra for PCF (2.1 mmol dm-3
) and MBP (0.9 mol dm-3
) in DCM (Figure
1(c) and (d)) at 30 ps, 100 ps, 300 ps and 700 ps. The two basis functions for the decomposition are shown in the
top panel: the TVA spectrum at a time delay of 20 ps was employed as a basis function for the 1PCF*(S1) state,
and that at 1000 ps for the 2PCF・
+ (D1) state. The validity of the latter assignment is confirmed by comparison
with the steady state FT-IR spectrum of 2PCF・
+(D1) obtained by the chemical oxidation method shown in Figure
S5.
0.0
0.2
0.4
Absorbance / mOD
0.0
0.2
0.4
Absorbance / mOD
1530 1540 1550 1560 1570 1580
0.0
0.2
0.4
Wavenumber / cm-1
0.0
0.2
0.4
Absorbance / mOD
0.0
0.2
0.4Absorbance / mOD
TVA spectra
30 ps
100 ps
300 ps
700 ps
1000 ps
20 ps
1PCF*(S1)
2PCF・+(D1)
TVA spectrum
Total fitting
Absorbance / mOD
S25
Figure S13: Decompositions of TEA spectra for: (left panel) PCH (2.1 mmol dm-3
) and MBP (1.8 mol dm-3
) in
DCM (Figure 4) at 5 ps, 10 ps, 25 ps and 50 ps; and (right panel) PCF (2.1 mmol dm-3
) and MBP (1.8 mol dm-3
)
in DCM (Figure 4) at 30 ps, 100 ps, 200 ps and 400 ps. The basis functions for decomposition are shown in
Figure S14.
30 ps
100 ps
200 ps
400 ps
5 ps
10 ps
25 ps
50 ps
1PCF*(S1)
2PCF・+(D1)
TEA spectrum
Total fitting
2PCH・+(D1)
1PCH*(S1)
Absorbance / mOD
400 450 500 550 600
0
5
10
15
Wavenumber / cm-1
0
5
10
15
0
5
10
15
0
5
10
15
0
10
20
0
10
20
0
10
20
400 450 500 550 600
0
10
20
Absorbance / mOD
Wavenumber / cm-1
S26
TEAS Basis Functions
Figure S14: Individual basis functions used to decompose the TEA spectra in Figure 4. The absorption spectra at
2 ps were taken as the absorption signatures of 1PCH*(S1) (left) or
1PCF*(S1) (right), and the spectra at 1200 ps
as those of the corresponding radical cations.
400 450 500 550 6000
10
20Absorbance / mOD
400 450 500 550 6000
10
20
Absorbance / mOD
400 450 500 550 6000
10
20
Absorbance / mOD
Wavelength / nm
PCH / Toluene
PCH / DCM
PCH / DMF
400 450 500 550 6000
10
400 450 500 550 6000
10
20
400 450 500 550 6000
10
Wavelength / nm
PCF / DMF
PCF / DCM
PCF / Toluene
1PCH*(S1) (2 ps)
2PCH.+(D1) (1200 ps)
1PCF*(S1) (2 ps)
2PCF.+(D1) (1200 ps)
1PCF*(S1) (2 ps)
1PCH*(S1) (2 ps)
1PCF*(S1) (2 ps)1PCH*(S1) (2 ps)
2PCF.+(D1) (1200 ps)
2PCH.+(D1) (1200 ps)
2PCH.+(D1) (1200 ps)
2PCF.+(D1) (1200 ps)
S27
Solvent Effects: TEAS Kinetic Traces
Figure S15: Kinetic traces for the TEA spectra in Figure 4 ([PCs]: 2.1 mmol dm-3
, [MBP]: 1.8 mol dm-3
). The
pseudo first-order time constants for PET τ'PET were obtained by fitting to single exponential functions for PCF
and biexponential functions for PCH (see main text). The time constants shown in the figure are the average
values for the decays of 1PC*(S1) state and the rise of
2PC
·+(D1) state. In the case of PCF/MBP in DMF the
observed lifetime was τobs = 153 ps; including the lifetime of 1PCF*(S1) in the absence of MBP, τ1 = 677 ps,
affords a time constant for the PET of τ’PET = 198 ps. In all other cases the S1 lifetime is significantly longer than
τobs, so τobs ~ τ'PET.
PCH / DMF: τʹPET1 = 5.6 ±0.6 ps
PCH / DCM: τʹPET1 = 7.0 ±2.2 ps
PCH / Toluene: τʹPET1 = 3.2 ±0.4 ps
PCF / DMF: τʹPET = 198 ± 7 ps
PCF / DCM: τʹPET = 170 ± 7 ps
PCF / Toluene: τʹPET = 135 ± 7 ps
2PCH・+(D1)
1PCH*(S1)
2PCH・+(D1)
1PCH*(S1)
2PCH・+(D1)
1PCH*(S1)
2PCF・+(D1)
1PCF*(S1)
2PCF・+(D1)
1PCF*(S1)
2PCF・+(D1)
1PCF*(S1)
τʹPET2 = 28 ±3 ps
τʹPET2 = 28 ±4 ps
τʹPET2 = 23 ±3 ps
0.0
0.2
0.4
0.6
0.8
1.0
Integrated intensity
0 50 100 150 200
0.0
0.2
0.4
0.6
0.8
1.0
Integrated intensity
Time / ps
0.0
0.2
0.4
0.6
0.8
1.0
Integrated intensity
0.0
0.2
0.4
0.6
0.8
1.0
Integrated intensity
0 200 400 600 800 1000
0.0
0.2
0.4
0.6
0.8
1.0
Time / ps
0.0
0.2
0.4
0.6
0.8
1.0
Integrated intensity
S28
Solvent Effects: Semi-logarithmic Plots of TEAS Kinetic Traces
Figure S16: Semi-logarithmic plots for Figure S15. The plots for PCH show non-single exponential behavior,
whereas those for PCF are linear.
1PCH*(S1)
2PCH・+(D1)2PCF・+(D1)
1PCF*(S1)
0 20 40 60 80 100-4
-3
-2
-1
0
DCM
DMF
toluene
log (intensity)
Time / ps
0 100 200 300 400 500-4
-3
-2
-1
0
DCM
DMF
toluene
log (intensity)
Time / ps
0 20 40 60 80 100-4
-3
-2
-1
0
DCM
DMF
toluene
log (1 - intensity)
Time / ps
0 100 200 300 400 500-4
-3
-2
-1
0
DCM
DMF
toluenelog (1 - intensity)
Time / ps
S29
Semi-logarithmic Plots for TVAS Measurements in DCM Solutions
Figure S17: Semi-logarithmic plots for the data presented in Figure 2.
PCH and MBP in DCM: TVA Spectra
Figure S18: TVA spectra for: (a) PCH (2.1 mmol dm-3
) in DCM; and (b) PCH (2.1 mmol dm-3
) and MBP (0.5
mol dm-3
) in DCM. Over 1530 – 1680 cm-1
there is significant spectral congestion, with vibrational absorptions
from at least three normal modes of 1PCH*(S1), two modes for
1PCH(S0) and, in the presence of MBP, from
2PCH
.+(D1) (Figure S6). Although this region was not decomposed successfully, the transient absorption from
2MP
.(D1) at 1660 cm
-1 in the presence of MBP was well-defined and therefore used to measure the rate of the
0 50 100 150 200-3
-2
-1
0
log (1 - intensity)
Time / ps
0 200 400 600 800 1000-3
-2
-1
0
log (1 - intensity)
Time / ps
(a) PCF (b) PCH
(a) PCH
(b) PCH + MBP2MP・(D1)
1550 1600 1650
-0.2
0.0
0.2
Wavenumber / cm-1
-0.2
0.0
0.2
Time / ps
1
10
50
200
500
Absorbance / mOD
S30
PET.
S31
PCF in DCM: TEAS Concentration Dependence
Figure S19: Kinetic traces for 1PCF*(S1) at various MBP concentrations with TEAS for 2.1 mmol dm
-3 PCF in
DCM solution, with pulsed photoexcitation at 370 nm, and pseudo first-order kinetic plot (inset), affording a
bimolecular rate coefficient of kPET = (4.4 ± 0.3) x 109 dm
3 mol
-1 s
-1. The kinetic traces were obtained using the
same method described in Figure S14.
1.2 1.8 2.4
0.005
0.010
k' PET / s-1
[MBP] / mol dm-3
1PCF*(S1)
0 200 400 600 800 1000
0.0
0.2
0.4
0.6
0.8
1.0
Integrated signal
Time / ps
S32
PCH: TEA Spectra
Figure S20: Transient electronic absorption spectra of PCH (2.1 mmol dm-3
) in (a) DMF; and (b) DCM,
following pulsed photoexcitation at 370 nm. In both solvents the decay of the 1PCH*(S1) state is accompanied by
the concomitant formation of a new transient species, assigned to 3PCH*(T1), which grows on too long a
timescale to determine a time constant. The new feature is present at the same position in both solvents and is
inconsistent with the absorption signature of the radical cation 2PCH
.+(D1); taken together, these observations
argue against any suggestion that 1PCH*(S1) decay may be due to electron transfer to the solvent. The lifetime of
the 1PCH*(S1) state is longest in DMF and shortest in DCM, but in both cases the time constant exceeds the
temporal range of our experiment (nanosecond timescale). The formation of a long-lived triplet state 3PCH*(T1) –
which might persist in more dilute solutions of MBP – may be one of the factors that makes PCH a poorer
photocatalyst for controlling polymer molecular weight and polydispersity in O-ATRP. Thermodynamically an
electron transfer from the first excited triplet state is strongly favored, as the 3PCH*(T1) state is not a great deal
lower in energy than the 1PCH*(S1) state and electron transfer from the latter state is seen to be diffusion-
controlled.
(a) DMF (b) DCM1PCH*(S1) 1PCH*(S1)
3PCH*(T1)
3PCH*(T1)
400 450 500 550 6000
10
20
30
Absorbance / m
OD
Wavelength / nm
Time / ps
10
200
300
500
800
1300
400 450 500 550 6000
10
20
30
Wavelength / nm
S33
Pure DCM: TEA spectra
Figure S21: Transient electronic absorption spectra of pure DCM following 370-nm excitation. The region at
around 370 nm is masked by the pump light.
Emission Spectra: PCF with/without Triplet Quenchers
Figure S22: Emission spectra for PCF in DCM with and without triplet quencher; pure DCM (∎), styrene (∎),
2,5-dimethylhexa-2,4-diene (DHD,∎), and cyclohexa-1-3-diene (CHD, ∎) following excitation at 370 nm. The
concentration of each triplet quenchers is 1 mol dm-3
. The apparent emission observed at around 450 nm for the
solution containing CHD is most likely due to subtle impurity in CHD.
400 450 500 550 600-5
0
5
10
15
Absorbance / mOD
Wavelength / nm
Time / ps
-0.20
0.00
0.05
0.10
0.50
1.00
2.00
(a)
450 500 550 600 650 7000
50
100
150
200
250
300
Emission intensity / arb. units
Wavelength / nm
without
quencher
styrene
DHD
CHD
(a)
S34
Triplet sensitization: PCF in DMF with benzophenone
A triplet sensitizer was added to the PCF solutions in DMF to explore the possible production of the
PCF(T1) triplet excited state using TEAS. The chosen sensitiser was benzophenone (Bzp) because its
triplet state lies sufficiently high in energy to sensitize the excitation of PCF(S0) to PCF(T1) by
intermolecular energy transfer. Figure S23 shows the resulting TEA spectra, and Figure S24
demonstrates that these TEA spectra can be decomposed into features attributed to PCF(S1) and Bzp(T1),
without having to invoke any additional spectral contributions – for example, from PCF(T1).
Figure S23: TEA spectra of a solution of PCF (2.1 mM) and benzophenone
(1.0 M) in DMF. The inset color key shows the time delay at which each
transient spectrum was acquired.
S35
Figure S24: Decomposition of selected TEA spectra of a solution of PCF (2.1 mM) and
benzophenone (1.0 M) in DMF into spectral components. The TEA spectra shown were
recorded at time delays of: (a) 30 ps; (b) 50 ps; (c) 100 ps; (d) 200 ps. The spectra used for
the decomposition are shown in panel (e) and were obtained from separate measurements
using PCF/DMF and Bzp/DMF solutions. The accelerated decay of the intensity of the PCF
band in the presence of Bzp is plotted in panel (f).
Steady-state emission measurements of a solution of 0.05 mM PCF and 2.5 mM benzophenone in DMF
showed no significant changes to the intensity of the PCF emission band compared to a 0.05 mM PCF
solution in DMF without added benzophenone. These measurements were made in a 1-cm quartz cuvette,
with an excitation wavelength of 370 nm at which both PCF and benzophenone absorb. This comparison
supports our assignment of the emission to fluorescence from PCF(S1), because phosphorescence from
the PCF(T1) state is expected to be enhanced by benzophenone acting as a triplet sensitizer.
S36
References
1. Roberts, G. M.; Marroux, H. J. B.; Grubb, M. P.; Ashfold, M. N. R.; Orr-Ewing, A. J., J. Phys.
Chem. A 2014, 118, 11211-11225.
2. Theriot, J. C.; Lim, C. H.; Yang, H.; Ryan, M. D.; Musgrave, C. B.; Miyake, G. M., Science 2016,
352, 1082-1086.
3. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.;
Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Vreven, T.; Montgomery, J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E.;
Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant,
J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G.
A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz,
J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Gaussian Inc., Wallingford CT, 2009.
4. Adamo, C.; Barone, V., J. Chem. Phys. 1999, 110, 6158-6170.
5. Marenich, A. V.; Cramer, C. J.; Truhlar, D. G., J Phys Chem B 2009, 113, 6378-6396.
6. Miertus, S.; Scrocco, E.; Tomasi, J., Chem Phys 1981, 55, 117-129.
7. Tomasi, J.; Mennucci, B.; Cammi, R., Chem. Rev. 2005, 105, 2999-3093.
8. Grimme, S.; Ehrlich, S.; Goerigk, L., J. Comput. Chem. 2011, 32, 1456-1465.
9. Goerigk, L.; Grimme, S., J. Chem. Theory Comput. 2011, 7, 291-309.
10. Essafi, S.; Tomasi, S.; Aggarwal, V. K.; Harvey, J. N., J. Org. Chem. 2014, 79, 12148-12158.
11. Adamo, C.; Jacquemin, D., Chem Soc Rev 2013, 42, 845-856.
12. Head-Gordon, M.; Rico, R. J.; Oumi, M.; Lee, T. J., Chem. Phys. Lett. 1994, 219, 21-29.
13. Laurent, A. D.; Jacquemin, D., Int. J. Quantum Chem. 2013, 113, 2019-2039.
14. Jacquemin, D.; Perpete, E. A.; Scuseria, G. E.; Ciofini, I.; Adamo, C., J. Chem. Theory Comput.
2008, 4, 123-135.
15. Peach, M. J. G.; Benfield, P.; Helgaker, T.; Tozer, D. J., J. Chem. Phys. 2008, 128, 044118
16. Yanai, T.; Tew, D. P.; Handy, N. C., Chem. Phys. Lett. 2004, 393, 51-57.
17. Werner, H.-J.; Knowles, P. J.; Knizia, G.; Manby, F. R.; Schütz, M.; Celani, P.; Korona, T.; Lindh,
R.; Mitrushenkov, A.; Rauhut, G.; Shamasundar, K. R.; Adler, T. B.; Amos, R. D.; Bernhardsson,
A.; Berning, A.; Cooper, D. L.; Deegan, M. J. O.; Dobbyn, A. J.; Eckert, F.; Goll, E.; Hampel, C.;
Hesselmann, A.; Hetzer, G.; Hrenar, T.; Jansen, G.; Köppl, C.; Liu, Y.; Lloyd, A. W.; Mata, R. A.;
May, A. J.; McNicholas, S. J.; Meyer, W.; Mura, M. E.; Nicklass, A.; O'Neill, D. P.; Palmieri, P.;
Pflüger, K.; Pitzer, R.; Reiher, M.; Shiozaki, T.; Stoll, H.; Stone, A. J.; Tarroni, R.; Thorsteinsson,
T.; Wang, M.; Wolf, A., MOLPRO, version 2010.1, a package of ab initio programs. see
http://www.molpro.net.
18. Werner, H. J.; Knowles, P. J., J. Chem. Phys. 1985, 82, 5053-5063.
19. Knowles, P. J.; Werner, H. J., Chem. Phys. Lett. 1985, 115, 259-267.
20. Silva, M. R.; Schreiber, M.; Sauer, S. P. A.; Thiel, W., J. Chem. Phys. 2010, 133, 174318.
21. Guido, C. A.; Knecht, S.; Kongsted, J.; Mennucci, B., J. Chem. Theory Comput. 2013, 9, 2209-2220.
22. Grubb, M. P.; Orr-Ewing, A. J.; Ashfold, M. N. R., Rev. Sci. Instrumen. 2014, 85, 064104.