Tuning J-aggregate Formation and Emission Efficiency in Cationic Diazapentacenium Dyes

Abstract

Enhancement of the luminescence efficiency of two new diazapentacenium salts (D1 and D2) of more than 55 for D1 and 22 times for D2) in poor solvents, acetonitrile and/or dichloromethane, was observed and rationalized as formation of emissive J-aggregates. Both compounds displaying 4-n-decylphenyl substituents at the 7,14-carbons and phenyl (D1) or 2,6-difluorophenyl (D2) substituents at the quaternary nitrogen atoms in 5,12-positions have been synthetized in a two-step procedure involving a two-fold Buchwald-Hartwig-type CN cross-coupling and an electrophilic Friedel-Crafts-type cyclization. The optical properties of the dicationic diazapentacenium salts in various solvents and in thin films have been investigated by steady-state and time-resolved absorption and photoluminescence spectroscopies. In thin films and in good solvents, isolated molecules coexist with aggregates. Nonetheless, D1 is seven times more emissive than D2, reflecting a higher J-aggregate contribution in the former.