Preparation and Photophysical and Photoelectrochemical Properties of Supramolecular Porphyrin Nanorods Structurally Controlled by Encapsulated Fullerene Derivatives

A new class of porphyrin nanorods structurally controlled by encapsulated fullerene derivatives is prepared via a solvent mixture technique. These nanorods, composed of fullerenes (C-60, C-60 derivatives and C-70) and zinc meso-tetra(4-pyridyl)porphyrin [ZnP(Py)(4)], are formed with the aid of a surfactant, cetyltrimethylammonium bromide (CTAB), in a DMF/acetonitrile mixture. In scanning electron microscopy (SEM) measurement, ZnP(Py)(4) pristine hexagonal nanotubes with a large hollow structure [denoted as ZnP(Py)(4) tube] are observed, whereas the hollow hole is completely closed in the case of nanorods composed of fullerenes (C-60 and C-70) and ZnP(Py)(4) [fullerene-ZnP(Py)(4) rod]. In C-60 derivative-ZnP(Py)(4) rods, the distorted polygonal columnar structures with large diameter and length are formed, its compared to the hexagonal structures of C-60-ZnP(Py)(4) and C-70-ZnP(Py)(4) rods. X-ray diffraction (XRD) analyses also reveals that ZnP(Py)(4) alignment in the nanorod is based on the stacked assemblies of ZnP(Py),1 coordinated hexagonal formations. Elemental analysis and titration experiment by absorption measurement were also performed to quantitatively check the relative molecular ratio between porphyrins and fullerenes. Steady-state and time-resolved fluorescence spectra show efficient fluorescence quenching, suggesting the forward electron-transfer process from the singlet excited state of ZnP(Py)(4) to fullerenes, Moreover, the back electron-transfer processes are detected by nanosecond transient absorption measurements. The forward and back electron-transfer rate constants are largely dependent oil the structures of the nanorods, To construct photoelectrochemical solar cells, fullerene-ZnP(Py)(4) rods are deposited onto nanostructured SnO2 films (OTE/SnO2). Fullerene-ZnP(Py)(4) rod-modified electrodes exhibited efficient light energy conversion properties, such its it power conversion efficiency (eta) of 0.63% and an incident photon to current conversion efficiency (IPCE) of 35%, which are much larger than those of ZnP(Py)(4) tube.