Photochemical Reaction Between 1,2‐Naphthoquinone and Adenine in Binary Water‐Acetonitrile Solutions

Abstract

The photochemical reaction between 1,2-naphthoquinone (NQ) and adenine was investigated using nanosecond time-resolved laser flash photolysis. With photolysis at 355nm, the lowest triplet state T1 of NQ was produced via intersystem crossing from its singlet excited state. The triplet-triplet absorption of the state contributes three bands of transient spectra at 374, 596 and 650nm, respectively, in pure acetonitrile and binary water-acetonitrile solutions. In the presence of adenine, the observation of A·+ (at 363nm) and NQ+H· radical (at 343 and 485nm) indicates a multistep mechanism of electron transfer process followed by a proton transfer between 3 NQ* and adenine. By fitting with the Stern-Volmer relationship, the quenching rate constant kq of 3 NQ* by adenine in binary water-acetonitrile solutions (4/1, volume ratio, v/v) is determined as 1.66×109 m-1 s-1 . Additionally, no spectral evidence confirms the existence of electron transfer between 3 NQ* with thymine, cytosine and uracil.