SITE-SELECTIVE FLUORESCENCE SPECTROSCOPY OF POLY(VINYLCARBAZOLE)

Site-selectively excited low-temperature fluorescence spectra are reported for matrix- isolated poly(styrene-co-vinylcarbazole) and poly(vinylcarbazole) in MTHF glass and for films of cationically and radically polymerized PVCA. The spectra of the copolymer indicate that isolated carbazole chromophores emit resonantly, the electron-phonon coupling constant being S ≤ 1. Both in PVCA/MTHF and PVCA film excitations execute a random walk, as expected for an energetically disordered system, if initially generated above a localization energy υloc within the low-energy tail of the inhomogeneously broadened distribution of intrinsic CA states (υloc = 28.380 cm-1 for PVCA/MTHF and 27.700 cm-1 for PVCA film). In the glass emission comes from states at υloc while in PVCA films structural traps (excimer-forming sites and trap II sites) capture the excitations involving a combination of random walk and long-range Förster transfer. Upon exciting at υex < υloc, defect states, showing up as a shoulder in the absorption and fluorescence excitation spectra of both PVCA/MTHF glasses and PVCA films, are populated directly, giving rise to fluorescence that shifts linearly with υex and displays a Stokes shift of 800 and 1100 cm-1, equivalent to an electron-phonon coupling constant S = 3. They are identified as the ground-state configurations of trap II. © 1990, American Chemical Society. All rights reserved.