Photoinduced processes of the supramolecularly functionalized semi-conductive SWCNTs with porphyrinsvia ion-pairing interactions

Abstract

Photoinduced electron transfer in self-assembled via ion-pairing porphyrin–SWCNT nanohybrids has been reported. To accomplish this, two kinds of semiconducting SWCNTs of different diameters, and free-base or zinc porphyrin bearing peripheral positive or negative charges serving as light absorbing photo-active materials are utilized. The donor–acceptor hybrids are held by ion-pairing with the help of oppositely charged pyrene derivatives adhered to the side walls of SWCNTs. Higher charge-separation efficiency is established for thick SWCNT(7,6) with narrower band gap compared with the thin SWCNT(6,5) with wider band gap. Photoelectrochemical studies using FTO/SnO₂ electrodes modified with these donor–acceptor nanohybrids unanimously demonstrated the ability of these nanohybrids to harvest light energy into electricity. Importantly, the photocurrent generation followed the trend observed for charge-separation, that is, incident-photon-to-current conversion efficiency of a maximum of 8% is achieved for photocells with SWCNT(7,6), while such conversion efficiencies are smaller for the cells derived from SWCNT(6,5). These results indicate that higher light energy conversion efficiencies are possible to achieve by the selection of the appropriate SWCNTs with right band gap on combination of appropriate porphyrins.