PHOTOPHYSICAL PROPERTIES OF A NEW CLASS OF DISCOTIC LIQUID-CRYSTALLINE COMPOUNDS - HEXA (DODECYL) HEXA PERI BENZYL CORONENE

The photophysical properties of hexa (dodecyl) hexa peri benzyl corone ne (HBC12), which displays a hexagonal columnar mesophase in a broad t emperature domain, have been studied in solution by steady state and t ime-resolved spectroscopy. These results have been compared with hexa (tertiary butyl) hexa peri benzyl coronene (HBC4) which does not show any liquid crystalline properties. The broadening of the stationary st ate absorption and fluorescence spectra of HBC12, upon increasing the concentration, suggests the formation of aggregates, which is in line with the multi exponential fluorescence decay of HBC12, observed with time resolved fluorescence experiments. Comparison with the non aggreg ating HBC4 allowed to attribute the longest decay time to the monomer species. The relative contribution of the short decay times in HBC12 i ncreases as a function of the concentration and the emission wavelengt h, which suggests that these decays are the result of an ensemble of a ggregated species.