Pulse radiolysis of chlorophyll a in solution

Pulse radiolysis of chlorophyll a (Chi a) in pure tetrahydrofuran (THF) and in tetrahydrofuran + 2% triethylamin (TEA) gives rise to a transient electronic absorption band with a maximum at 455 nm. The lifetime and chemistry of this transient strongly depend upon the presence of triethylamin. In pure tetrahydrofuran the transient undergoes a fast second-order decay with a typical half-life of ∼ 8 us, and an apparent second-order rate constant 2 k = 1.5 • 1010 M-1 s-1 is determined.

The initial spectrum is replaced by a long-lived residual absorption with maxima at 465 and 480 nm. In tetrahydrofuran + 2% triethylamin the typical half-life is 400 us, and the products show absorptions at 470 and 520 nm. These results are discussed and the 455 nm transient is tentatively assigned to the radicalanion of Chi a, while the 520 nm product is assigned to β/δ-dihydrochlorophyll a (Krasnovsky's pigment).