**2.4 Organic-light emitting diodes (***O***-LEDs)**

The light-emitting diode (LED) is a light-emitting semiconducting material when current flows through it. The current flow induced light emission was first observed by Captain Henry Joseph Round in 1907. Light emission takes place when electrons undergo a transition from the conduction band to the empty valence band. The band gap in semiconducting material decides the color of emitted light. *O*-LED are

the LEDs in which the light-emissive electroluminescent film is made up of organic molecules. In the case of *O*-LEDs the highest occupied molecular orbital (HOMO) is the conduction band, and the lowest unoccupied molecular orbital (LUMO) is the empty valence band of organic substance. *O*-LEDs are preferred over LEDs due to the facts that an *O*-LED is thinner and have a better display property; it has brighter, fast responsive, and long-range contrast display. Moreover, *O*-LEDs have wider viewing angles with low driving voltage property. *O*-LEDs can be conveniently fabricated on a glass surface at low temperatures. Organic semiconducting materials are in the crystalline or polymeric phase. Organometallic compounds, polymers, and even simple organic molecules like aryl amines are used in *O*-LEDs. The research in the field of *O*-LEDs is in rapid progress as these displays are already in use in modern electronic and optoelectronic appliances like heads-up displays, billboard-type displays, automotive dashboards, home and office lighting, and flexible displays. The synthetic invention of these organic moieties is a progressive field, and the microwave-assisted synthetic methods of *O*-LEDs have also started sprouting in recent years [60, 61].

The amalgamation of organic moieties and inorganic matrices results in the synergetic effects by augmenting of the properties like flexibility and shape ability with stability [62]. Poly (2-hydroxyethyl methacrylate) (PHEMA) silica-hybrids have been prepared by microwave irradiation [63]. Organoboron dye diketonate BF2 complex **77**, borondipyrromethene (BODIPY) **78**, and (1,3-boron di(iso)indomethene dye **79** can be integrated into these PHEMA silica hybrids.

N,N-Diphenylamine (DPA) were transformed to form precursors for *O*-LEDs using solid state microwave-assisted organic synthetic method [64]. This reaction was carried out in the MAS II SINEO microwave reactor in presence of Iodine and alumina. The temperature range of 125–133°C was optimized and the reaction was completed in 15 minutes at 500–600 W power of the reactor. After typical work up procedure they ended up with two fractional mixtures of compounds **80** to **85** with fluorescence property were obtained.

**73**

*Microwave Synthesized Functional Dyes DOI: http://dx.doi.org/10.5772/intechopen.94946*

sors, photochromic materials, OLEDs, etc.

the Karnatak University, Dharwad.

**Acknowledgements**

**3. Conclusions**

Polyfluorene is regarded as an important source for the development of *O*-LEDs. It emits blue light and the color of the light can be tuned by means of doping, structural engineering, preparing materials with tuned properties [65]. Microwave-assisted synthesis of π conjugated polymers were reported and this method was proved to be an advantageous method over multi-step expensive conventional method. They have effectively used microwave conditions in oxidative polymerization of 2,5-diphenyl-1,3,4-oxadiazole and 9,9-dihexyl-fluorene monomers to get poly (dihexyl fluorene-co diphenyl oxadiazole) (POF) **86** in the presence of FeCl3 catalyst.

Since from the centuries, dyes have played a very important role in human life. The functional dyes have changed the technologies drastically and have gained immense importance now a day. A specific property of the dye depends on the various factors such as the donor, electron acceptor/π-conjugation, linker, etc. present at appropriate positions. More effort has been established into searching for better dyes with expected properties. Microwave-assisted synthesis has changed the methodology of organic synthesis and hence is also efficiently applied in the synthesis of functional dyes. Therefore, a number of dyes synthesized under microwaves along with their applications were discussed. There is a possibility for further development in organic synthetic methodology under microwaves to obtain dyes having wider applications in organic photovoltaics, fluorescence sen-

The authors thank the DST, New Delhi for the sanction of PURSE Phase -II to

*Microwave Synthesized Functional Dyes DOI: http://dx.doi.org/10.5772/intechopen.94946*

Polyfluorene is regarded as an important source for the development of *O*-LEDs. It emits blue light and the color of the light can be tuned by means of doping, structural engineering, preparing materials with tuned properties [65]. Microwave-assisted synthesis of π conjugated polymers were reported and this method was proved to be an advantageous method over multi-step expensive conventional method. They have effectively used microwave conditions in oxidative polymerization of 2,5-diphenyl-1,3,4-oxadiazole and 9,9-dihexyl-fluorene monomers to get poly (dihexyl fluorene-co diphenyl oxadiazole) (POF) **86** in the presence of FeCl3 catalyst.
