PHOTOTAUTOMERISM OF 5-DEAZALUMICHROME (IN THE PRESENCE OF ACETIC-ACID)

The phototautomerism of 5-deazalumichrome was studied in 1,2-dichloroe thane in the presence of acetic acid. In comparison with 3-methyllumic hrome, 5-deazalumichrome undergoes excited state proton transfer with higher efficiency, manifested by its fluorescence spectrum and lifetim es. The replacement of N-5 by carbon in the pyrazine ring of alloxazin e restricts the electron density redistribution involved in the photot automerism to the region of N-1:C-10a:N-10, and eliminates the competi tive contribution of the rest of the conjugated double bond system. Se miempirical calculations confirm the experimental observations.