Perylene liquid crystals with multiple alkyl chains: investigation of the influence of peripheral alkyl chain number on mesomorphic and photophysical properties

Abstract

Herein, a series of mesogenic perylene bisimide (PBI) dyes including 1,6,7,12-tetrachloroperylenebisimides 11a, 11b and 11c with 2, 4 and 6 peripheral alkyl chains at the imide positions and 1,6,7,12-tetra-p-nonylphenol bay-substituted perylene bisimides 12a, 12b and 12c with 6, 8 and 10 peripheral alkyl chains at both the imide and bay-positions were synthesized and characterized. The influence of multiple peripheral alkyl chains on the mesomorphic and photophysical properties was investigated. The results suggested that all of them possessed hexagonal columnar mesophases. The presence of more alkyl chains contributed to lower phase transition temperature and more orderly hexagonal mesophases. These novel perylene liquid crystals exhibited excellent fluorescence properties with fluorescence quantum yields of 0.90–0.96 in solution. The compounds 12a, 12b and 12c presented larger Stoke shifts and higher Φ_F values than the compounds 11a, 11b and 11c; this indicated that more peripheral alkyl chains at both the imide and bay-positions contributed to the excellent fluorescence properties in both solution and thin films.