Vijaya Gopalan Sree

Synthesis, optical and electrochemical properties of poly(N-bromo-2-ethynylpyridinium bromide)

ABSTRACT Poly(N-bromo-2-ethynylpyridinium bromide) was synthesized via the catalyst-free polymerization of 2-ethynylpyridine using bromine in high yield. The activated triple bonds of N-bromo-2-ethynylpyridinium bromide formed at the initial quaternization reaction are susceptible to linear polymerization, followed by an identical propagation step that contains the produced macroanion and quaternized N-bromo-2-ethynylpyridinium bromide species. The chemical structure of polymer was characterized by various instrumental methods to have the conjugated polymer backbone system bearing the designed N-bromo-2-pyridinium bromide substituents. The optical and electrochemical properties of polymer were studied. The UV-visible spectrum of polymer showed a characteristic absorption peak in the visible region (up to 800 nm). The photoluminescence emission spectrum of polymer shows two distinct peaks at 407 and 516 nm. The cyclic voltammetry of polymer exhibited irreversible electrochemical behavior between the oxidation and reduction peaks.

Highly efficient deep-red emitting methyl substituted thiophenylquinoline based Ir(III) complexes for solution-processed organic light-emitting diodes

ABSTRACT Herein, we synthesized two new methyl substituted thiophenyl-quinoline based heteroleptic Ir(III) complexes as guest molecules for deep-red emitting solution-processed phosphorescent organic light-emitting diodes (PhOLEDs). Their thermal stabilities, photophysical properties and electroluminescence (EL) properties are systematically investigated. (MTPQ)2Ir(pic) and (MTPQ)2Ir(acac) showed photoluminescence emission of 614 and 629 nm and a photoluminescence quantum yield of 21% and 15%, respectively. Solution-processed deep-red emitting PhOLEDs were fabricated using standard structure with PEDOT:PSS and TPBi as hole and electron transport layers, respectively and, a mixed host of TCTA:TPBi (1:1) doped with the guest Ir(III) molecules. The emission electroluminescence wavelength was slightly red shifted by 11 nm for both (MTPQ)2Ir(pic) (625 nm) and (MTPQ)2Ir(acac) (640 nm). A maximum external quantum efficiency of 8.46% and maximum current efficiency of 7.37 cd/A was achieved for (MTPQ)2Ir(pic) with a deep-red CIE coordinates of (0.679, 0.318).

High efficient vacuum deposited red organic light-emitting diodes compared with their solution-processed counterpart

ABSTRACT Herein, we demonstrate dry- and wet-process feasible red (PhQ-Th)3Ir complex as dopant and improved external quantum efficiency (EQE) of the device by 30.17% though vacuum-process using the same device structure. The turn-on voltage is reduced to less than 3 V by adopting vacuum deposition process. The vacuum-processed devices showed EQE and power efficiency of 26.75% and 28.90 lm/W, respectively, with turn on voltage of 2.83 V. The maximum luminance is increased from 1088 cd/m2 to 6396 cd/m2 using dry-process. It is found that the difference in device performance is attributed to their morphological variance of solution- and vacuum-processed devices.