Analysis of branched oligophenylene by absorption and fluorescence spectra

Abstract

A branched oligophenylene has been synthesized based on 1,3,5-tri(4′-bromophenyl)benzene. Absorption and fluorescence spectra were studied and fluorescence quantum yields and lifetimes were measured for the compound in solution. It is demonstrated that the absorption spectrum is a superposition of p-quaterphenyl, p-terphenyl, and biphenyl chromophore absorption bands in a 1:2:1 ratio. The oligomer fluorescence spectrum is found to depend on the excitation wavelength. It is shown that the oligomer fluorescence is determined by two fluorochromic groups, namely fragments with branched p-terphenyl and p-quaterphenyl units. The main fluorescence maxima for these fluorochromic groups coincide with each other and lie in the vicinity of λ = 360 nm. A very weak fluorescence band found in the region 380–440 nm is excited by light with a wavelength lying beyond the oligomer self-absorption region. The reasons for a decrease in fluorescence quantum yields of branched models and the studied oligophenylene as compared with those of linear p-polyphenylene chromophores are discussed.