Light- and pH-driven electron transfer in the pyranine–methylviologen system

A face-to-face electrostatic complex is formed in alkaline solution by pairing the trisodium salt of 8-hydroxy-1,3,6-pyrenetrisulfonic acid (pyranine tsPyOH,3Na+), an anionic donor, with the dichloride salt of methyl viologen (MV2+, 2Cl−), a cationic acceptor. The donor displays dual properties: it can be photoionized or can transfer an electron to the acceptor. It is shown that light absorption by the self-assembled complex leads to the formation of a particularly short-lived species (3.7 ps) assigned to a singlet excited state which relaxes to the ground state via a charge-transfer state.