New glass forming triarylamine based azomethines as a hole transport materials: Thermal, optical and electrochemical properties

New, solution processable azomethines, consisting of electron-donating triarylamine units (TPA) were synthesised via condensation of 4-formyltriphenylamine with 1,5-diaminonaphthalene, 1,4-diaminonaphthalene, 3,3'-dimethylnaphtidine and 3,8-diamino-6-phenylphenanthridine in view of their potential application in organic (opto)electronics. The structures of the compounds were characterized by means of IR, NMR spectroscopy and elemental analysis; the results show an agreement with the proposed structure. The prepared azomethines exhibited glass-forming properties with glass-transition temperatures in the range of 102-222 degrees C. Optical properties of the prepared compounds were investigated by UV-Vis and photoluminescence (PL) measurements. The obtained compounds emitted blue-green light in chloroform solution with emission maximum (lambda(em)) at ca. 500 nm and blue one (lambda(em) similar to 440 nm) in blend with PMMA. The electrochemical behavior of azomethines was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The HOMO level was in the range from -5.08 to -5.22 eV. The HOMO, LUMO levels and energy band gap (E-g) were additionally calculated theoretically at B3LYP/6-31G(d,p) level. It was found that imine obtained from 1,4-diaminonaphthalene exhibited better conjugation than other TPA-based azomethines. Preliminary electrical conductivity measurements were carried out on ITO/compound/Al devices. (C) 2012 Elsevier B.V. All rights reserved.