Photoinduced intramolecular charge-transfer systems based on porphyrin–viologen dyads for optical limiting

Photoinduced intramolecular charge transfer in porphyrin–viologen dyads has been investigated as a potential method leading to optical limiting in the nanosecond range. Solutions of these dyads in acetonitrile were studied by picosecond and nanosecond time-resolved fluorescence and absorption spectroscopy. Both methods give evidence of efficient photoinduced charge separation. Nonlinear transmission measurements around 600 nm with nanosecond laser pulses have shown that the dyad solution leads to a lower transmission at high incident fluences (>1 J/cm2) than the model porphyrin solution. Moreover, this dyad solution is more efficient than a solution of porphyrin with added viologen, both solutions having the same quenching efficiency.