On/off switching of perylene tetracarboxylic bisimide luminescence by means of substitution at the N-position by electron-rich mono-, di-, and trimethoxybenzenes

A series of perylene tetracarboxylic bisimides, substituted at the N-position with methoxyphenyl groups, have been synthesized together with model compounds and their photophysical properties have been investigated by means of steady-state and time-resolved spectroscopic techniques. The luminescence properties of the examined compounds vary remarkably with the substitution pattern, with emission quantum yields ranging from 1 to 10(-2)-10(-3). The observed quenching of the luminescence is assigned to a photoinduced electron transfer (PET) from the electron-rich methoxybenzene unit to the perylene bisimide moiety. The radical anion of perylene bisimide has been detected by transient-absorption spectroscopy. The results could satisfactorily be explained by taking into consideration the redox potentials of the partners and the electron-releasing ability of each methoxy group in relation to its position with respect to N. Quantum-chemical calculations were also performed.