of bis dicarboximides was easily separated chromatographically the pbdcl derivatives embodied in compounds 1 and 2 can be reversibly reduced with either one or two electrons at thermodynamic half wave potentials e sub 1 2 spsb 0 50 v and e sub 1 2 spsb 2 0 73 v versus a saturated calomel electrode in pyridine while e sub 1 2 spsb for one electron oxidation of the porphyrin is 0 92 v these data and the following equation 2 below show that pbdcl is an excellent electron acceptor the pbdcl and pbdcl 2 ions have characteristic intense optical absorptions at 713 and 546 nm respectively this opens up the possibility that rapid photoinduced electron transfers from donor molecules may be used to selectively reduce pbdcl with either one or two electrons the resultant photochromic changes in absorption from 713 to 546 nm could form the basis for molecular switches based on optimized molecular absorption characteristics photoinduced reduction of pbdcl by the lowest excited singlet state of hp was detected readily with transient optical absorption spectroscopy pyridine solutions 5 u00d7 10 5 m of compounds 1 and 2 depicted in fig1 and 2 wherein r 1 r 2 and r 3 were all pentyl groups were excited with 160 femto second fs 1 fs 10 5 seconds laser pulses at 585 nm with a 1 khz repetition rate the optical absorbances of the samples at 585 nm were 0 3 and were limited by the solubility of these compounds in pyridine time resolved transient absorption spectra of compounds 1 and 2 after excitation were monitored with a femtosecond white light continuum the overall instrumental response was 200 fs the diameter of the excitation.