Stable Photoinduced Charge Separation in Nanostructured Films Containing a 1,4,5,8-Naphthalenetetracarboxylic Diimide and Cytochrome <I>c</I>

Abstract

Photoinduced electron transfer between 1,4,5,8-naphthalenetetracarboxylic diimides (NDI) and the redox protein cytochrome c (cyt c) was studied in solution and in spin-coated thin films. The NDI derivatives employed in this study were N,N'-bis(butyl)-1,4,5,8-naphthalenetetracarboxylic diimide (BNDI) and N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenetetracarboxylic diimide (PNDI). Irradiation of the NDI in solution with UV light (365 nm), in the presence of cyt c, resulted in the reduction of the heme iron from the Fe3+ to the Fe2+ state. When PNDI and cyt c were co-deposited by spin-coating on quartz, glass, and silicon substrates, photoactive films were obtained. Exposition of the films to a UV lamp or natural sun light resulted in photoreduction of the protein, generating a stable charge-separated state. Thin films containing segregated layers of BNDI and cyt c were also prepared. Irradiation of these films, however, resulted in protein degradation. The results can be explained through the formation of imide radicals, which transfer an electron to cyt c in the co-deposited films. In the case of segregated films, protein photodegradation suggests the formation of singlet oxygen within the films.

Scanning Tunneling Microscopy and Orbital-Mediated Tunneling Spectroscopy of N,N′-Dioctyl-1,8:4,5-naphthalenediimide Adsorbed on Highly Ordered Pyrolytic Graphite from Various Solvents and in Different Environments

“…Santos et al 40 showed that a dibutyl version of the diimide was readily reduced once excited to the triplet state. Rodrigues and co-workers observed that naphthalenediimide triplet states cause photooxidation of tryptophan.…”

“…Although diimides have seen extensive use in supramolecular chemistry, mainly as electron acceptor units, 39 there is little previous work on the STM and electronic spectroscopy of adsorbed diimide but more on its analogues. Santos et al 40 showed that a dibutyl version of the diimide was readily reduced once excited to the triplet state. Rodrigues and co-workers observed that naphthalenediimide triplet states cause photooxidation of tryptophan.…”