Synthesis and optical properties of novel asymmetric perylene bisimides

A novel series of asymmetric perylene bisimides, 1-amino-7-nitroperylene bisimides (1a-1c), was synthesized and fully characterized. These molecules undergo an excited-state intramolecular electron transfer reaction, resulting in a unique charge transfer emission in the near-infrared region, of which the peak wavelength exhibits strong solvatochromism. The dipole moments of these compounds have been estimated using the Lippert-Mataga equation, and upon excitation, the molecules show larger dipole moment changes than those of the symmetric 1,7-diaminoperylene bisimides (2a-2c). Furthermore, these dyes undergo two quasi-reversible one-electron oxidations and two quasi-reversible one-electron reductions in dichloromethane at modest potentials. They display good thermal stability and optical stability that can be used as stable near-infrared fluorescent dyes. Their spectroscopic properties in various conditions and complementary time-dependent density functional theory calculations are reported.