Steric Effect on Dimer Radical Cation Formation of Poly(3,6-di-tert-butyl-9-vinylcarbazole) and Its Dimeric Model Compounds Studied by Laser Photolysis

Abstract

The steric effect of bulky tert-butyl group on the formation of a dimer radical cation was investigated. Transient absorption spectra for poly(3,6-di-tert-butyl-9-vinylcarbazole) (PBVCz) and its dimeric model compounds were measured by laser photolysis. Though the interaction was weak compared with the case of carbazole chromophores, all these compounds formed the dimer radical cation and gave the dimer band in a visible region and the charge-resonance (CR) band around ca. 2000 nm. This is quite in contrast to the result that the meso isomer of 2,4-bis(3,6-di-tert-butyl-9-carbazolyl)pentane and 1,3-bis(3,6-di-tert-butyl-9-carbazolyl)propane do not form an intramolecular excimer. In these compounds, two chromophores cannot come close together and the dimer radical cation has a rather loose conformation. This means that the conformational requirement for the formation of the dimer radical cation is rather loose and that the stabilization energy is larger than that of the excimer. In PBVCz, interactions among more than two chromophores are hindered and the partially-overlapped dimer radical cation is formed in contrast to the case of poly(N-vinylcarbazole).