The photodynamics of 2,4-diaminopyrimidine in comparison with 4-aminopyrimidine: The effect of amino-substitution

Abstract Nonadiabatic photodynamical surface hopping simulations of 4-aminopyrimidine and 2,4-diaminopyrimidine were performed at multi-configurational level. Additional NH 2 substitution blocks part of the ring puckering modes necessary to reach ultrafast deactivation channels but does not affect the excited-state lifetime of 2,4-diaminopyrimidine significantly since other pathways leading to ultrafast relaxation can be utilized. The effect of the excess energy on the relaxation mechanism of 2,4-diaminopyrimidine was studied. It is shown that the amount of initial energy influences the time to reach the crossing seam and thus the lifetime. This study is important when interpreting the experimental results performed at different pump energies.