PHOTOPHYSICS OF CARBAZOLE-CONTAINING SYSTEMS .1. DILUTE-SOLUTION BEHAVIOR OF POLY(N-VINYL CARBAZOLE) AND N-VINYL CARBAZOLE METHYL ACRYLATE COPOLYMERS

Steady-state and time-resolved fluorescence techniques have been used to study the photophysical behaviors of poly(N-vinyl carbazole), PNVCz and a series of N-vinyl carbazole-methyl acrylate (NVCz-co-MA) copoly mers in dilute solution as a function of both NVCz composition and tem perature. A kinetic scheme, intended to describe intramolecular excime r formation across the entire NVCz composition range, is proposed. In low aromatic content copolymers, two monomer species (unquenched and q uenched monomer) and two excimer species (the sandwich-like excimer an d a higher energy excimer) exist. The contribution from monomer emissi on to the overall fluorescence decreases with increasing NVCz content through increased excimer formation: this is likely to be consequent u pon (1) an increase in the number of excimer forming sites, and (2) in creasing efficiency of energy transfer from the excited monomers to th e excimer forming sites. In the homopolymer, PNVCz, the only emission that can be observed on a nanosecond timescale is excimeric. This fluo rescence appears to originate from three excimer species (the sandwich -like excimer, and two higher energy forms). For the homopolymer, the current observations are consistent with the model proposed by Vandend riessche and De Schryver [Polym. Photochem. 7, 153 (1986)]. (C) 1997 J ohn Wiley & Sons, Inc.