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 having either four bis(4'-tert-butylbiphenyl-4-yl)aniline or phenathiazine were designed.
• The dyads were titrated with imidazole appended fullerenes, C60Im or C70Im, to form supramolecular triads, and binding constant found ~ 2 × 104 M-1.
• In these triad systems, zinc porphyrin and fullerenes act as primary electron donor and acceptors while PTZ/BBA act as secondary electron donors.

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 1H 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[C60]pyrrolidine or N-Methyl-4-(1H-imidazol-1-yl)phenylfullero[C70]pyrrolidine and supramolecular triads of the type, (PTZ or BBA)4-ZnP:(C60Im or C70Im) 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 1H 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[C60]pyrrolidine or N-Methyl-4-(1H-imidazol-1-yl)phenylfullero[C70]pyrrolidine indicating the occurrence of photo-induced electron transfer from 1ZnP⁎ to co-ordinated fullerene moieties.

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