Multifunctional polyconjugated molecules with carbazolyl and pyrazolyl moieties for optoelectronic applications

• Published in: Synthetic metals Vol. 160; no. 5; pp. 490 - 498
• Main Authors: Arbačiauskienė, E., Kazlauskas, K., Miasojedovas, A., Juršėnas, S., Jankauskas, V., Holzer, W., Getautis, V., Šačkus, A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2010; Elsevier
• Subjects: Analogue; Carbazole; Charge carrier mobility; Chemistry; Cyano groups; Decay; Derivatives; Diethylene derivatives; Electron affinity; Electrostatics; Exact sciences and technology; Excitons; Fluorescence; Heterocyclic compounds; Heterocyclic compounds with only one n hetero atom and condensed derivatives; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Ionization potential; Light-emitting diodes; Organic chemistry; Preparations and properties; Pyrazole; Diethylene derivatives; Fluorescence; Ionization potential; Carbazole; Pyrazole; Charge carrier mobility; Electrostatic effect; Exciton; Nitrile; Nitrogen heterocycle; Electron affinity; Photoluminescence; Luminescent material; Thin film; Steric effect; Decay time; Optical properties; Dilute solution; Pyrazole derivatives; Chemical synthesis; Chemical solution; Deactivation; Electrical properties; Carbazole derivatives; Steric hindrance; Quantum yield; Molecule scattering; Solid state; Analog; Organic light emitting diodes; Conjugated compound
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/j.synthmet.2009.11.038

Diethylene derivative possessing carbazolyl and pyrazolyl moieties and its analogue containing additional cyano groups were synthesized and investigated as potential multifunctional materials for organic light emitting diodes. The influence of the electron affinitive cyano groups on the ionization potential ( I p ) of the films as well as on the photoluminescence (PL) spectrum, PL quantum yield ( η) and PL decay time of the dilute solutions and thin films of the diethylene derivatives was studied. PL measurements revealed that highly luminescent ( η = 0.80) cyano-free pyrazole–carbazole derivative in solution became weakly emissive ( η = 0.04) by attaching cyano groups as a result of these groups-induced torsional deactivation. However in the solid state, the steric and electrostatic effects of the bulky and polar cyano groups prevented close packing of the molecules, thus significantly reducing migration-induced quenching of the excitons at the defects. Incorporation of the cyano groups resulted in the 3-fold enhancement of the PL quantum yield in the neat film of the polyconjugated derivative as compared to that of the cyano-free film. The I p of 5.50 eV estimated for the cyano groups-containing compound was found to be higher as compared to the I p of 5.35 eV for the cyano-free analogue, which in conjunction with the PL data for the films indicated increased electron affinity (by 0.40 eV) in the cyano groups-containing diethylene derivative.