Triplet Excimer Formation of Dibromocarbazole Chromophores in Methacrylate Copolymer Films Measured by Time-Resolved Phosphorescence and Transient Absorption Spectroscopy

Abstract

Time-resolved phosphorescence and transient absorption spectroscopy have been carried out for studying the triplet states of the 3,6-dibromocarbazole (DBCz) chromophore in a solid matrix of methacrylate copolymer. poly[2-(3,6-dibromo-9-carbazoyl)ethyl methacrylate-co-methyl methacrylate]. The sample film containing 10% DBCz units showed critical behavior in the time-resolved phosphorescence spectra which altered the shape from the monomer state [sup 3]M* to two kinds of excimer states: E1 and E2 (460 and 510 nm at the maximum intensity, respectively). These excimeric species have identical profiles with those reported for poly(3,6-dibromo-9-vinylcarbazole), although the polymer structures are totally different. This result shows that the DBCz chromophores tend to take some preferential geometry which results in the formation of two distinct excimer sites in the polymer film. The spectral alteration with time was drastically accelerated by thermal activation in the temperature range 25-77 K. Iterative trapping and detrapping processes determine the rate of relaxation to the deeper traps, E1 and E2. 15 refs., 8 figs., 1 tab.