Influence of liquid crystalline solvents — cholesteryl oleyl carbonate and 4-n-octyl-4′-cyanobiphenyl — on fluorescence of exciplex of perylene and N. N-dimethylaniline

Abstract

Abstract The influence of the phase state of the liquid crystalline solvents 4- n -octyl-cyanobiphenyl (8CB) and cholesteryl oleyl carbonate (COC) on the flourescence of the intermolecular perylene— N , N -dimethylaniline (DMA) exciplex was studied. The introduction of DMA into perylene solutions in COC or 8CB gives rise to exciplex fluorescence indicated by the extension of the long-wavelength region of the spectrum. Exciplex fluorescence was observed in all phase states of the liquid crystalline solutions, i.e. crystalline, nematic and isotropic phases of 8CB and smectic, cholesteric and isotropic phases of COC. Exciplex formation occurs by a static mechanism in crystalline and smectic phases of 8CB and COC as a result of the excitation of perylene—DMA complexes in the ground state. On going from the smectic to the cholesteric phase of COC, deformation of the exciplex fluorescence band occurs. Similar changes are observed in the case of 8CB. The analysis of the influence of temperature on the fluorescence spectrum of the exciplex shows that, in liquid crystalline solutions, two types of exciplex can exist which differ in their structure and localization within the liquid crystalline matrices.