Light-induced energy and electron transfer occurring in tandem in tetra (bis(4′-tert-butylbiphenyl-4-yl)aniline)-zinc(II) porphyrin-fullerene supramolecular conjugates

Abstract

[Formula: see text]-bis (4′-tert-butylbiphenyl-4-yl)aniline) tethered zinc porphyrins, (BBA)4- ZnP, (BBA- Ph)4- ZnP, and (BBA- OEtOPh)4- ZnP with varied spacer distances have been synthesized and photosynthetic antenna-reaction center models were constructed via axial co-ordination with fulleropyrrolidines, C60Im and C70Im. Selective excitation of the BBA moiety in the porphyrins at 355 nm resulted in the quenching of the emission intensity of the BBA followed by the concomitant appearance of the ZnP emission at 600–640 nm indicating the occurrence of the photoinduced energy transfer from 1BBA* to ZnP. When the zinc porphyrins are titrated with C60Im and C70Im, supramolecular complexes of the type, (BBA)4-ZnP:[Formula: see text]Im/[Formula: see text]Im are formed and the complex formation was monitored by UV-visible spectroscopic studies. Steady-state fluorescence studies involving the excitation of the ZnP at 550 nm displayed the diminished fluorescence intensity of the ZnP emission indicating the photoinduced electron transfer from 1ZnP* to fullerenes. More interestingly, when the BBA moiety is excited in the supramolecular complexes, the emission of both the BBA and ZnP were decreased gradually indicating the occurrence of PEnT from 1BBA* to ZnP followed by a sequential electron transfer from 1ZnP* to C60Im or C70Im indicating the formation of a charge-separated state in these complexes.