A series of derivatives of the titled compound with donor and acceptor substituents were prepared. Efficient fluorescence quenching was observed for the molecules in which donor and acceptor pi -chromophores are coplanar. Charge recombination of the radical ion pairs resulted in broad charge transfer bands centered at ca. 510 nm. Twisting the donor and acceptor chromophores 90 degrees with respect to each other seemed to retard the electron transfer process. (C) 2000 Elsevier Science Ltd. All rights reserved.