Spectral characteristics of bisthiophenes and terthiophenes linked with heterocyclic unit in solution and polymer matrix

Spectral characteristics of derivatives of thiophene substituted on hetoroaromatic cycle as pyrazine was compared with terthiophene linked with cyano and hydrazo groups. The absorption, fluorescence and its lifetime were measured in solution (methanol, cyclohexane) and in polymer matrices (polystyrene, PS; polymethyl methacrylate, PMMA; and polyvinyl chloride, PVC). Derivatives with two thiophene units substitute on pyrazine exhibit the lowest wavenumber band in the region 26,320-25,600cm(-1) and log epsilon similar to4.0, which is not influenced by the medium. Derivatives with benzene and pyridine ring annealed to pyrazine (2,3-bis-(2 -thienyl)quinoxaline (I), 2,3-bis-(2'-thienyl)pyrido[2,3-b]pyrazine (III)) exhibit fluorescence in polar methanol with maximum at 22,200cm(-1) and quantum yield of about 0.2 which is blue-shifted in going to non-polar solvent. The maximum fluorescence is slightly blue-shifted in polymer matrices as compared to methanol. Derivatives with annealed thiophene to pyrazine or substituted with two cyano groups (2,3-bis-(2'-thienyl)thieno[3,4-b]pyrazine (II), 2,3-dicyano-5,6-bis(2'-thienyl)pyrazine (IV)) do not yield any emission. Derivatives with terthiophene structural units ([2,2',5',2 "]-terthiophene-[2]-thienylacrylonitrile (V) [2,2',5',2 "]-terthiophene-5-carbaldebydehydrazone (VI)) exhibit fluorescence with maximum around 20,000 cm(-1). The lifetime of fluorescence of all thiophene was 1 ns or shorter. The polymer matrices increase the intensity of fluorescence to some extent and prolong the lifetime of thiophene derivatives. Derivative VI exhibits some tendency to an aggregation at higher concentration above 0.01 mol kg(-1) in polymer matrices. (C) 2001 Elsevier Science B.V. All rights reserved.