Photoinduced Electron Transfer between Chlorophyllaand Gold Nanoparticles

Abstract

Excited-state interactions between chlorophyll a (Chla) and gold nanoparticles have been studied. The emission intensity of Chla is quenched by gold nanoparticles. The dominant process for this quenching has been attributed to the process of photoinduced electron transfer from excited Chla to gold nanoparticles, although because of a small overlap between fluorescence of Chla and absorption of gold nanoparticles, the energy-transfer process cannot be ruled out. Photoinduced electron-transfer mechanism is supported by the electrochemical modulation of fluorescence of Chla. In absence of an applied bias, Chla cast on gold film, as a result of electron transfer, exhibits a very weak fluorescence. However, upon negatively charging the gold nanocore by external bias, an increase in fluorescence intensity is observed. The negatively charged gold nanoparticles create a barrier and suppress the electron-transfer process from excited Chla to gold nanoparticles, resulting in an increase in radiative process. Nanosecond laser flash experiments of Chla in the presence of gold nanoparticles and fullerene (C60) have demonstrated that Au nanoparticles, besides accepting electrons, can also mediate or shuttle electrons to another acceptor. Taking advantage of these properties of gold nanoparticles, a photoelectrochemical cell based on Chla and gold nanoparticles is constructed. A superior performance of this cell compared to that without the gold film is due to the beneficial role of gold nanoparticles in accepting and shuttling the photogenerated electrons in Chla to the collecting electrode, leading to an enhancement in charge separation efficiency.

Quenching of chlorophyll fluorescence induced by silver nanoparticles

“…In fact, direct binding of a fluorophore to the metal surface in general results in the quenching of excited states [26]. Furthermore, by analyzing the interaction between Chl molecules and gold nanoparticles (AuNPs), Barazzouk and co-workers has also demonstrated that the main suppression process of the ChlF was induced by the photoinduced electron transfer from excited Chl to AuNPs [27].…”

Chlorophyll a fluorescence in two varieties of sugar cane subjected to aluminum and water stress

“…When in high concentrations, metals may cause a range of significantly different effects (Ralph and Burchett, 1998) like changes in both electron transfer and enzyme activities (Li et al 2010). Barazzouk et al (2005), based on electrochemical studies, attributed the effect of photoinducted electron transfer of excited chlorophyll to nanoparticles of gold. For these authors, electron transfer is a dominant process when one considers the differences in chlorophylls' oxidation potential.…”

In vivo observation of chlorophyll fluorescence quenching induced by gold nanoparticles

“…Two competing effects could induce changes in the efficiency of a photosystem: the increase in light absorption by chlorophyll molecules, due to plasmon resonance (enhanced local field near the metal surface [17]); and energy transfer from chlorophyll to metallic nanoparticles, by inducing a decrease in the quantum yield of the photosynthetic system. Recently, Barazzouk et al reported that the emission intensity of Chla could be quenched by gold nanoparticles in a solution medium [18]. This quenching has been attributed to the process of photoinduced electron transfer from excited Chla to gold nanoparticles.…”