The photochemistry of a variety of dicyanopyridines (2,3-, 2,4-, 2,5-,
2,6-, 3,4- and 3,5-dicyanopyridine) in solution at room temperature w
as investigated. Pulsed UV (308 nm) laser irradiation in deoxygenated
acetonitrile yields the triplet state with lifetimes between 4 and 10
mu s and absorption bands in the 400 and 320 nm regions. In the presen
ce of added HCl an air-insensitive transient (tau approximate to 10-12
mu s, lambda(max)approximate to 360-380 nm) was observed, suggesting
the formation of a protonated excited state. Irradiation in the presen
ce of amines resulted in the production of the pyridyl radical anion (
tau approximate to 40-80 mu s, air sensitive, lambda(max)approximate t
o 360-380 nm) formed by electron transfer from the amine to the pyridi
ne triplet excited state. Stem-Volmer analysis gave electron transfer
rate constants in the range (1-8)X10(-8)M(-1)s(-1). In methanol solven
t, irradiation yielded an air-insensitive transient assigned as the ne
utral pyridyl radical (tau approximate to 30-200 mu s, lambda(max)appr
oximate to 370-385 nm). The formation of these transients is discussed
in the context of previous photochemical electron spin resonance and
product studies.