Synthesis and spectroscopic studies of axially bound tetra(phenothiazinyl)/tetra(bis(4′-tert-butylbiphenyl-4-yl)aniline)-zinc(II)porphyrin-fullero[C60 & C70]pyrrolidine donor–acceptor triads

Two zinc porphyrin based dyads, 5, 10, 15, 20-tetra-4-(2-(10H-phenothiazin-10-yl)ethoxy)phenyl porphyrinato zinc (II) and 5,10,15,20-tetra-4-(bis(4′- tert -butylbiphenyl-4-yl)amino)phenyl porphyrinato zinc(II) containing four phenothiazine or bis(4′-tert-butylbiphenyl-4-yl)aniline moieties tethered to porphyrin framework were synthesized, and systematically characterized using 1 H NMR, mass, UV–visible and steady state fluorescence techniques. Excitation of 5,10,15,20-tetra-4-(bis(4′- tert -butylbiphenyl-4-yl)amino)phenyl porphyrinato zinc(II) at 335 nm, resulted in quenched emission of bis(4′- tert -butylbiphenyl-4-yl)aniline moiety, when compared to pristine bis(4′- tert -butylbiphenyl-4-yl)aniline, and appearance of porphyrin emission at 618 nm, due to intramolecular energy transfer from bis(4′-tert-butylbiphenyl-4-yl)aniline moiety to porphyrin. The porphyrin dyads were titrated with phenylimidazole appended fullerenes, N -Methyl-4-(1H-imidazol-1-yl)phenylfullero[C 60 ]pyrrolidine or N -Methyl-4-(1H-imidazol-1-yl)phenylfullero[C 70 ]pyrrolidine and supramolecular triads of the type, (PTZ or BBA) 4 -ZnP:(C 60 Im or C 70 Im) were formed in which, zinc porphyrin and fullerenes act as primary electron donor and acceptors, while phenothiazine or bis(4′-tert-butylbiphenyl-4-yl)aniline moieties behave as secondary electron donors in photo-induced electron transfer events. Optical absorption and 1 H NMR titration studies confirmed the formation of supramolecular triads and the steady state fluorescence experiments revealed the quenching of porphyrin emission upon addition of increasing amounts of N -Methyl-4-(1H-imidazol-1-yl)phenylfullero[C 60 ]pyrrolidine or N -Methyl-4-(1H-imidazol-1-yl)phenylfullero[C 70 ]pyrrolidine indicating the occurrence of photo-induced electron transfer from 1 ZnP ⁎ to co-ordinated fullerene moieties.