Asymmetric perylene bisimide dyes with strong solvatofluorism

Two asymmetric perylene bisimide dyes, 1-cyano-7-piperidinylperylene bisimide (1) and 1-bromo-7-piperidinylperylene bisimide (2), were synthesized and fully characterized. These molecules undergo an excited-state intramolecular electron transfer reaction, resulting in a unique charge transfer emission, of which the peak wavelength exhibits strong solvatochromism. They show both larger ground-state and excited-state dipole moments than those of the symmetric perylene bisimide 3; the dipole moments of these compounds have been estimated using density functional theory calculations and the Lippert-Mataga equation. Furthermore, these dyes (1-3) display good thermal stability as well as good optical stability and reversible redox properties. Their spectroscopic properties in various conditions and complementary time-dependent density functional theory calculations are reported. (C) 2013 Elsevier Ltd. All rights reserved.