Anomalous spin polarization in the photoreduction of chromone-2-carboxylic acid with alcohol induced by hydrochloric acid

The addition effect of hydrochloric acid (HCl) on the photoreduction of chromone-2-carboxylic acid (CRCA) is studied by time-resolved EPR. The EPR lines of CRCA ketyl radical show an enhanced absorption in the presence of HCl, while without HCl these show an emissive character. On the other hand, the lines of the CRCA alkyl type radical show an emissive character whether HCl is included or not. The simultaneous reactions of the closely-lying two excited triplet states (T1 and T2) of CRCA may induce the above anomalous CIDEP behavior.