Synthesis of fluorene derivatives

Theoretical Study on Polyfluorene

By Dinesh Varma IIT Guwahati

Why Polyfluorene? Polyfluorenesare a class ofpolymericmaterials. They are of interest because similar to otherconjugated polymers, they are currently being used inlight-emitting diodes,field-effect transistors, and plastic solar cells.

The synthesis of monomers based on alkylated fluorene which can be then copolymerized with other monomers to form conjugated copolymers whose band gap is tuned by the regular insertion of the an electron-donating or electron-withdrawing units, (3,4-ethylenedioxy)thiophene and pyridine, respectively.

What is fluorene?Fluorene, a principal repeat unit in polyfluorene derivatives, was isolated fromcoal tarand discovered by Marcellin Berthelotprior to 1883.Its name originates from its interestingfluorescence. Fluorene became the subject of chemical-structure relatedcolor variation(visible rather than luminescent).

Structure of fluorene

Polyfluorene derivatives used in..These are commonly and extensively used in the fabrication of devices such as Plastic Solar cells and Organic Light Emitting Diodes (OLEDs) mainly.

In OLEDs, polyfluorenes are desirable because they are the only family of conjugated polymers that can emit colors spanning the entire visible range with high efficiency and low operating voltage.

Organic Solar CellsAnorganic solar cellorplastic solar cellis a type ofpolymer solar cellthat usesorganic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules,for light absorption and charge transport to produceelectricityfromsunlightby thephotovoltaic effect.

Why Plastic Solar CellsThe plastic used in organic solar cells has low production costs in high volumes. Combined with the flexibility of organicmolecules, organic solar cells are potentially cost-effective for photovoltaic applications.Molecular engineering (e.g. changing the length andfunctional groupofpolymers) can change the energy gap, which allows chemical change in these materials. Theoptical absorption coefficientof organic molecules is high, so a large amount of light can be absorbed with a small amount of materials.

Clean Energy Supply Needed for Quality of LifeFossil and nuclear fuels are costly. If we include the environmental cost.The sun shines on everyone. Ideal for distributed power generation and remote location.Tap solar energy directly Ideal for distributed power generation More environmental friendly

Annual sum of Global Irradiance

Area of solar cell needed..With 10% efficient solar cell area of solar cell needed in 2004 India 60 km 60 km (0.12% area) World need: 350 km 350 km

Annual Variation of solar insolation

The energy (or insolation) received on a surface throughout the year varies relatively little from year to year.

History1839 Photovoltaic effect discovered by Edmond Becquerel1954 First Silicon Solar Cell inBell Lab by Chapin, Fuller and Pearson (6%)1970s Surge in research to harness solar energy1986 Heterojunction Organic Solar Cell by Tang of Eastman Kodak2007 Highest efficiency solar cells with ~40.7% in SpectrolabA big surge in solar cells research & development is underway

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Applications

Applications

Solar Energy Usage and Pricing

Solar Energy: 30 c (Rs. 12) per kWhNeed to lower cost to 10c (Rs.4) per kWh and belowSolar markets(average of last 5 years)Solar Price/Competing Energy sourceRemote Industrial 17% 0.1-0.5 timesRemote habitation 22% 0.2-0.8 timesGrid Connected 59% 2-5 timesConsumer Indoor 2% n/a

Electricity Generation CostEnergy SourceCostCombined cycle gas turbine3 -5 (Rs.1.20-Rs.2.00)Wind4 -7 (Rs.1.60-Rs.2.80)Biomass gasification7 -9 (Rs.2.80-Rs.3.60)Remote diesel generation20 -40 (Rs.8.00-Rs.16.00)Solar PV central station20 -30 (Rs.8.00-Rs.12.00)Solar PV Distributed20 -50 (Rs.8.00-Rs.20.00)

Solar Energy Production and Price

Lowering Cost of Solar Cells

Thin Film Solar Cells Multiple junction solar cells (a-Si:H, a-SiGe:H) CdTe based cells (CdTe, CdS) CuInSe2 (CIS) Ternary & Multinary compound solar cells Multicrystalline/Microcrystalline silicon solar cells Thin film GaAs solar cells Organic solar cells

Why Organic Solar Cells?High-Throughput and Low-Cost Processing Printing Screen Pringing Stamping Spraying Spin Coating Vaporisation

Flexible Solar Cells Flexible Surfaces Conformal Surfaces

Eco-Friendly Technology Appropriate Process Biodegradable Molecule

Polyfluorene materials used in OLEDs and Plastic Photovoltaics

Other Organic materials used in OLEDs and Plastic Photovoltaics

What is an OLED ?OLED - Organic Light Emitting Diode

An OLED is a light emitting diode (LED) which emissive electroluminescent layer is composed of a film of organic compounds

HISTORYFirst developed in the early 1950s in France.1960s-AC-driven electroluminescent cells using doped anthracene was developed.In 1987 Chin Tang and Van Slyke introduced the first light emitting diodes from thin organic layers.In1990 electroluminescence in polymers was discovered.

ARCHITECTURE OF OLED

SUBSTRATE.

ANODE

ORGANIC LAYER: 1-Conductive layer 2-Emmisive layer

CATHODE

TYPES OF OLED

Passive OLEDsThe organic layer is between cathode & anode run perpendicular.

The intersections form the pixels.

Easy to make.

Use more power.

Best for small screens.

Active OLEDsFull layers of cathode and anode.

Anode over lays a thin film transistor (TFT).

Requires less power.

Higher refresh rates.

Suitable for large screens

APPLICATIONS OF OLED

TelevisionsSONYLG transparent TV

Cell Phone screens

Wrist WatchComputer ScreensLaptopsDesktops

Bendable DevicesPortable Device displaysPhilips Go Gear MP3 Player

ADVANTAGES

Faster response time than LCDs Consume significantly less energy Can be transparent when offFlexible and Conformal Displays Thinner display-No backlight requiredBetter contrast ratioSafer for the environmentWider viewing angles; up to 170 degreesOLEDs refresh almost 1,000 times faster then LCDsLow cost materials and fabrication methodLess Expensive than LCD due to lesser componentsCan be made using plastic screens; LCDs require glass backing

FUTURE USES FOR OLED

Data glassGPS systemOLED in future carsCurved OLED displays, placed on non-flat surfacesAnd many more we cannot even imagine today

Scroll LaptopNokia concept OLED Laptop

DefinitionsElectroluminescence(EL) is anoptical phenomenonandelectrical phenomenonin which a material emits light in response to anelectric currentpassed through it, or to a strongelectric field Apixel (or picture element) is the smallest item of information in an imageAthin-film transistor(TFT) is a special kind offield-effect transistormade by depositingthin filmsof asemiconductoractive layer.Therefresh rateis the number of times in a second that display hardware draws the data it is being given

OLED TV

Flexible OLED

Samsung's 40-inch OLED TV

LG Display 19-inch OLED

FAST RESPONSE TIME

LCDOLEDFast response time means full motion graphics can be displayed

CONSTANT CONTRAST RATIOWide viewing angle.

SONY PSP2 CONCEPT

Oled rollable display.

A flexible OLED display that can be rolled around the main electronics core but, when charged, automatically stiffens with minimal bezel surround.

BENDABLE OLED DISPLAYOrganic Light Emitting Diode (OLED) technology is threatening the Liquid Crystal Display, or LCD, standard because of its flexibility, low power consumption and versatility.

OLED vs LCD

My Experimental Work I reported the synthesis and characterization of two monomers based on alkylated fluorene namely 2,7-Dibromo-9,9-didecylfluorene and 2,7-Bis[4,4,5,5-tetramethyl-(1,3,2)-dioxaborolan-2-yl]-9,9didecylfluorene which can then copolymerized with other monomers to form conjugated copolymers. The monomers synthesized are neither polymerized nor tested for the applications due to some limitations in doing, but copolymers of similar compounds such as 2,7-Dibromo-9,9-dioctylfluorene and 2,7-Bis[4,4,5,5-tetramethyl-(1,3,2)-dioxaborolan-2-yl]-9,9dioctylfluorene have optical properties such that they are suitable materials for device developments such as electrochromics, PLEDs, and solar cells

Reaction Scheme

Method 1:

Method 2:

ResultsFirst two steps of the method 1 are successful but unfortunately the final step i.e synthesis of 2,7-Bis[4,4,5,5-tetramethyl-(1,3,2)-dioxaborolan-2-yl]-9,9didecylfluorene is not achieved.Then by following Method 2 we are able to synthesize both the monomers. Due to some limitations in techniques as well as time to synthesize and characterize the polymers which can be prepared using these monomers is not performed.

ConclusionAs Solar cells and OLED technology is vastly growing now-a-days I aimed to synthesize few molecules which can be used in the fabrication of Solar cell and OLED devices.

ReferencesAll images are taken from Google Images.Solar Cells data is from www.solarbuzz.com.

Thank You