Kanagaraj Shanmugasundaram

Utilization of a phenanthroimidazole based fluorophore in light-emitting electrochemical cells

An easily accessible, highly soluble, small-molecule phenanthroimidazole derivative has been synthesized and characterized. The synthesized compound shows strong luminescence in solution and exhibits good thermal stability. Single crystal X-ray crystallography studies were carried out. Correlations between the X-ray structures, photophysical properties and the performance in light-emitting electrochemical cells (LECs) are described. A yellowish green emission was achieved by using the target compound in a LEC device configuration. The constructed prototype device performance was promising with a maximum brightness of 125 cd m−2. The results suggest that the phenanthroimidazole derivative can function as an active material in LEC devices.

Blue and Blue-Green Light-Emitting Cationic Iridium Complexes: Synthesis, Characterization, and Optoelectronic Properties

Two new cationic iridium complexes, [Ir(ppy)2(phpzpy)]PF6 (complex 1) and [Ir(dfppy)2(phpzpy)]PF6 (complex 2), bearing a 2-(3-phenyl-1H-pyrazol-1-yl)pyridine (phpzpy) ancillary ligand and either 2-phenylpyridine (Hppy) or 2-(2,4-difluorophenyl)pyridine (Hdfppy) cyclometalating ligands, were synthesized and fully characterized. The photophysical and electrochemical properties of these complexes were investigated by means of UV-visible spectroscopy, emission spectroscopy, and cyclic voltammetry. Density functional theory (DFT) and time dependent DFT (TD-DFT) calculations were performed to simulate and study the photophysical and electrochemical properties of both complexes. Light-emitting electrochemical cells (LECs) were fabricated by incorporating complexes 1 and 2, which respectively exhibit blue-green (488 and 516 nm) and blue (463 and 491 nm) emission colors, achieved through the meticulous design of the ancillary ligand. The luminance and current efficiency measurements recorded for the LEC based on complex 1 were 1246 cd m(-2) and 0.46 cd A(-1), respectively, and were higher than those measured for complex 2 because of the superior balanced carrier injection and recombination properties of the former.

Non-doped deep blue light-emitting electrochemical cells from charged organic small molecules

Blue emitters are still elusive for solid-state light-emitting electrochemical cells, and limit the development of white light emitting devices for display applications. We report the photophysical, electrochemical, thermal and electroluminescence properties of two charged organic deep blue-emitters. The synthesized materials showed intense blue fluorescence with high quantum efficiencies and good thermal stabilities. Single-layered non-doped LEC devices were fabricated from solution. The fabricated non-doped LEC devices exhibited deep blue electroluminescence centered at 432 and 434 nm with the CIE coordinates of (0.15, 0.09) and (0.16, 0.10), respectively for compounds 1 and 2, which are quite close to the National Television System Committee (NTSC) standard for blue color coordinates. Electroluminescent devices operated at very low turn-on voltages reveal maximum luminance of 118 cd m−2 for compound 1 and 136 cd m−2 for compound 2. These promising results are highly desirable for the development of low cost white light-emitting devices.

Phenothiazine based blue emitter for light-emitting electrochemical cells

A butterfly shaped phenothiazine based electroluminescent material PPPSO2 was synthesized as an ionic small molecule emitter for light-emitting electrochemical cells (LECs). PPPSO2 shows deep blue emission in solution with high fluorescent quantum yield of 0.49. By employing the active molecule PPPSO2 as an emitter in LECs, the device shows electroluminescence centered at 498 nm with CIE coordinates of (0.21, 0.31) and maximum luminance of 509 cd m−2. The results show that the versatility of phenothiazine based luminescent materials such as high thermal stability and different emission color by tuning the oxidation state makes phenothiazine derivatives a prospective material for light-emitting devices.

Small Molecule-Based Light-Emitting Electrochemical Cells

Organic small molecules (SM) offer excellent opportunities to construct cheap, sustainable, and efficient electroluminescent devices due to the availability of a wide range of synthetic procedures and the ability to fine-tune their photophysical and electrochemical properties. Fascinated by the high performances of SMs in organic light-emitting diodes (OLEDs), considerable amount of effort has been put forward by material scientist to find efficient methods to utilize SMs in light-emitting electrochemical cells (LEC). This chapter covers the incorporation of SM into light-emitting electrochemical cells (SM-LEC), which are categorized according to the function of the SM in the active layer of LECs. The structures and properties of the family of SM used up to date are discussed in this chapter with a special emphasis on their role in the device mechanism and the effect of the molecule charge.