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

Spectral characteristics of derivatives of thiophene substituted on hetoroa romatic cycle as pyrazine was compared with terthiophene linked with cyano and hydrazo groups. The absorption, fluorescence and its lifetime were meas ured in solution (methanol, cyclohexane) and in polymer matrices (polystyre ne, PS; polymethyl methacrylate, PMMA; and polyvinyl chloride, PVC). Deriva tives with two thiophene units substitute on pyrazine exhibit the lowest wa venumber 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 pyr idine ring annealed to pyrazine (2,3-bis-(2 -thienyl)quinoxaline (I), 2,3-b is-(2'-thienyl)pyrido[2,3-b]pyrazine (III)) exhibit fluorescence in polar m ethanol with maximum at 22,200cm(-1) and quantum yield of about 0.2 which i s blue-shifted in going to non-polar solvent. The maximum fluorescence is s lightly blue-shifted in polymer matrices as compared to methanol. Derivativ es 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'-th ienyl)pyrazine (IV)) do not yield any emission. Derivatives with terthiophe ne structural units ([2,2',5',2 "]-terthiophene-[2]-thienylacrylonitrile (V ) [2,2',5',2 "]-terthiophene-5-carbaldebydehydrazone (VI)) exhibit fluoresc ence 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 deriv atives. Derivative VI exhibits some tendency to an aggregation at higher co ncentration above 0.01 mol kg(-1) in polymer matrices. (C) 2001 Elsevier Sc ience B.V. All rights reserved.