Proton coupled electron transport of pH sensitive coumarin based ruthenium(II) complex: A functional mimic of photosystem II

Abstract

In this work, we have explored a new pH sensitive coumarin based ruthenium(II) complex (R1QC) to mimic the role of P680 in donor side of photosystem II in natural photosynthesis. R1QC underwent protonation at higher H+ ion concentration to form a protonated complex (R1QCH+) which exhibited excited state intramolecular proton transport phenomenon. So as to mimic the proton coupled electron transport reactions those take place in the donor side of PS II after light excitation, the interaction between protonated Ru(II) complex and 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone) in 1:1-acetonitrile:water solution at pH 10 was investigated by absorption, emission and electrochemical measurements. In the protonated complex (R1QCH+), Ru2+ core behaves as electron donor whereas coumarin based ligand behaves as proton donor to the quinone. This proton coupled electron transport interaction mimics the proposed reduction of the donor side of PS II.

Keywords

• Photosystem II
• Proton coupled electron transport
• Ruthenium complex
• Coumarin
• Fluorescence enhancement