The effect of substituent groups in bis(dithiobenzil) nickel compounds on their absorption spectra, reduction potential and singlet oxygen quenching efficiency

The influence of substituents on the longest wavelength (Λmax) of absorption maxima and the reduction potential of bis(p‐substituted dithiobenzil) nickel compounds has been evaluated by the classical Hammett equation. A good linear relationship between Λmax or reduction potential and σp or σp+ shows that at least one phenyl ring is conjugated with the five‐membered nickel chelate ring, although neither of the phenyl rings is actually coplanar to the chelate ring. The amount of singlet oxygen quenched by bis(p‐substituted dithiobenzil) nickel has been conveniently measured by means of a gas chromatograph using a capillary column.