FLUORESCENCE OF PYRENYL AND CARBAZOLYL DERIVATIVES IN LIQUID SOLUTIONAND SOLID FILM

A systematic investigation of the effects of stereochemistry and solid -state morphology on emission characteristics were performed using gla ss-forming pyrenyl and carbazolyl derivatives as neat films in PMMA an d cholesteric liquid crystalline glass. At high dilution in tetrahydro furan, pyrenyl derivatives were prone to form intramolecular excimers whereas carbazolyl derivatives showed no evidence for excimers. Both p yrenyl and carbazolyl derivatives at 10(-3) to 10(-2) M in isotropic a nd ordered solid hosts exhibited mostly monomer emission. In neat film s, intermolecular excimers prevailed in pyrenyl derivatives whereas ca rbazolyl derivatives showed evidence for monomer emission as well. One feature that distinguishes carbazolyl derivatives from poly(N-vinylca rbazole) is the observed fine structures:in the fluorescence spectra o f thin films. Order parameters characterizing the helical alignment of pyrenyl and carbazolyl pendants with a cholesteric host were determin ed with circularly polarized fluorescence spectroscopy. The results in dicate the relative ease of aligning pyrenyl groups, presumably becaus e of the more favorable regiochemistry and conformational flexibility.