The semireduced transients of proflavin were studied in airfree acid aqueous solutions by a combined pulse radiolysis-computer optimization procedure. The main product, semiquinone (C-radical; 75%), formed with k=6.4 × 109dm3mol-1s-1 , decays by dimerisation (2k=2 × 109dm3mol-1s-1) and dismutation (2k=0.5 x 109dm3mol-1s-1). It possesses several absorption bands (ε270 = 1900, ε360 = 1530, ε460 = 2250 and ε530 = 200 m2mol-1 ). The second transient, R·-species (N-radical; 16.5%), is produced with k=1.4 × 109dm3mol-1s-1 and decays preferentially by transformation into semiquinone with k = 2 × 105s-1; its absorption bands are: ε295 = 2300, ε380 = 1000, ε440 = 5000 and ε680 = 530m2mol-1. Finally H-adducts on various positions of the aromatic ring (8.5%) are arising with k = 0.7 × 109dm3mol-1s-1 , decay according to a pseudo first order reaction, k = 1.1 × 104s-1, and have absorption bands at ε270 = 2100 and ε435 = 1580m2mol-1. The obtained results are of particular interest for the photochemical and photoelectrochemical solar energy utilization.
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