Improving Photocurrent Generation: Supramolecularly and Covalently Functionalized Single-Wall Carbon Nanotubes-Polymer/Porphyrin Donor-Acceptor Nanohybrids

Novel nanohybrids based on covalently and noncovalently functionalized single-wall carbon nanotubes (SWNTs) have been prepared and assembled for the construction of photoactive electrodes. Polymer-grafted SWNTs were synthesized by free-radical polymerization of (vinylbenzyl)trimethylammonium chloride. Poly[(vinylbenzyl)trimethylammonium chloride] (PVBTA(n+)) was also noncovalently wrapped around SWNTs to form stable, positively charged SWNT/PVBTA(n+) suspensions in water. Versatile donor-acceptor nanohybrids were prepared by using the electrostatic/van der Waals interactions between covalent SWNT-PVBTA(n+) and/or noncovalent SWNT/PVBTA(n+) and porphyrins (H2P8- and/or ZnP8-). Several spectroscopic, microscopic, transient, and photoelectrochemical measurements were taken to characterize the resulting supramolecular complexes. Photoexcitation of the nanohybrids afforded long-lived radical ion pairs with lifetimes as long as 2.2 Vs. In the final part, photoactive electrodes were constructed by using a layer-by-layer technique on an indium tin oxide covered glass support. Photocurrent measurements gave remarkable internal photon-to-current efficiencies of 3.8.1 and 9.90% for the covalent ZnP8-/SWNT-PVBTA(n+) and noncovalent ZnP8-/SWNT/PVBTA(n+) complex, respectively, when a potential of 0.5 V was applied.