STUDIES OF THE TRIPLET-STATE PROPERTIES OF HYPOCRELLIN-A BY NANOSECOND FLASH-PHOTOLYSIS

Hypocrellin A (HA) is an efficient phototherapeutic agent. Its triplet properties have been investigated in cyclohexane using the nanosecond flash photolysis technique. The triplet-triplet (T-T) absorption spec trum of HA gives three bands with absorption maxima at around 520, 555 and 600 nm. The triplet energy level for HA has been estimated to be about 42.5 kcal mol-1 by the energy transfer method. The extinction co efficients for the T-T absorption of HA have been determined by the gr ound state depletion method. The triplet quantum yield of HA is 0.78 /- 0.04 (by reference to benzophenone).