Asymmetric perylene bisimide dyes with strong solvatofluorism

• Asymmetric and symmetric 1,7-disubstituted perylene bisimide dyes were synthesized.
• These dyes undergo an excited-state intramolecular electron transfer reaction.
• The asymmetric molecules show both larger ground-state and excited-state dipole moments than those of the symmetric one.

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.

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