Photoinduced charge separation in three-layer supramolecular nanohybrids: fullerene–porphyrin–SWCNT

Photoinduced charge separation processes of three-layer supramolecular hybrids, fullerene–porphyrin–SWCNT, which are constructed from semiconducting (7,6)- and (6,5)-enriched SWCNTs and self-assembled via π–π interacting long alkyl chain substituted porphyrins (tetrakis(4-dodecyloxyphenyl)porphyrins; abbreviated as MP(alkyl)4) (M = Zn and H2), to which imidazole functionalized fullerene[60] (C60Im) is coordinated, have been investigated in organic solvents. The intermolecular alkyl–π and π–π interactions between the MP(alkyl)4 and SWCNTs, in addition, coordination between C60Im and Zn ion in the porphyrin cavity are visualized using DFT calculations at the B3LYP/3-21G(*) level, predicting donor–acceptor interactions between them in the ground and excited states. The donor–acceptor nanohybrids thus formed are characterized by TEM imaging, steady-state absorption and fluorescence spectra. The time-resolved fluorescence studies of MP(alkyl)4 in two-layered nanohybrids (MP(alkyl)4/SWCNT) revealed efficient quenching of the singlet excited states of MP(alkyl)4 (1MP*(alkyl)4) with the rate constants of charge separation (kCS) in the range of (1–9) × 109 s−1. A nanosecond transient absorption technique confirmed the electron transfer products, MP˙+(alkyl)4/SWCNT˙− and/or MP˙−(alkyl)4/SWCNT˙+ for the two-layer nanohybrids. Upon further coordination of C60Im to ZnP, acceleration of charge separation via1ZnP* in C60Im→ZnP(alkyl)4/SWCNT is observed to form C60˙−Im→ZnP˙+(alkyl)4/SWCNT and C60˙−Im→ZnP(alkyl)4/SWCNT˙+ charge separated states as supported by the transient absorption spectra. These characteristic absorptions decay with rate constants due to charge recombination (kCR) in the range of (6–10) × 106 s−1, corresponding to the lifetimes of the radical ion-pairs of 100–170 ns. The electron transfer in the nanohybrids has further been utilized for light-to-electricity conversion by the construction of proof-of-concept photoelectrochemical solar cells.