Photo-induced proton transfer in crystalline 2-(2',4'-dinitrobenzyl)py
ridine is characterized by transient absorption between 10 and 300 K.
Temperature independent and thermally activated processes are identifi
ed. The long-lived colored tautomer is shown to be formed by two compe
ting routes, one on short time scales in the excited state and the oth
er in the ground state via intermediate tautomers.