Nonradiative decay of the lowest excited singlet state of 2-aminopyridine is considerably faster than the radiative decay.

Ab initio calculations reveal that radiative lifetime of the lowest excited singlet state of 2-aminopyridine molecule should be around 20 ns, consistent with the molecules of the same type but is about one order of magnitude larger than the claimed experimental fluorescent lifetime in recent years. An S(1)/S(0) conical intersection close to the S(1) state has been located, which could be the possible nonradiative channel that is responsible for the fast decay observed in the experiment.