CONCERNING THE ABSORPTION AND EMISSION PROPERTIES OF PHENANTHRO[1,10,9,8,O,P,Q,R,A]PERYLENE-7,14-DIONE

In contrast to hitherto published data, phenanthro[1,10,9,8,o,p,q,r,a] perylene-7,14-dione, the fundamental chromophoric system of hypericin type compounds, exhibits an absorption with a long wavelength band at 423 nm in aprotic solvents like dimethylsulfoxide (epsilon approximate to 7000). Its fluorescence in these solvents is below the detection l imit. In protic solvents like methanol, the long wavelength absorption is bathochromically shifted to 546 nm, and a fluorescence at 565 nm i s observed. This behavior was interpreted from the reversal of n - pi and pi - pi transitions. The data have not been recorded yet due to the very low solubility of this compound. Its monoprotonation in groun d and excited states is characterized by pK(a) and pK(a) values of -6 and 2; diprotonation occurs at a pK(a) = -7.