Ab initio study of the photochemistry of aminopyrimidine

Abstract

Complete active space self-consistent field (CASSCF), multi-reference configuration interaction calculations (MR-CISD), and equation of motion coupledcluster with singles and doubles (EOM-CCSD) calculations are presented in order to elucidate the photodeactivation pathways of 6-aminopyrimidine after vertical excitation to the S 1 1 n* state. Vertical excitation energies are reported up to the S 7 state. Two S 1 excited state minima, both of 1 n* character, and three strongly puckered 1 * minima on the crossing seam (MXS) between the S 0 and the S 1 potential energy surface were found. Nonadiabatic reaction paths are discussed by linearly interpolating between the two minima and all MXS, which explain and extend observations made in recent surface-hopping dynamics CASSCF investigations Lischka, J Phys Chem A 2007, 111, 2852].State-averaged complete active space self-consistent field (SA-CASSCF) and multireference configuration interaction calculations with single and double excitations (MR-CISD) calculations were carried out for the optimization of stationary points and conical intersections, calculation of excitation energies, and search for reaction paths. In the FIGURE 1. Structure and labeling of 6AP.

Photophysics of Structurally Modified Flavin Derivatives in the Blue‐Light Photoreceptor YtvA: A Combined Experimental and Theoretical Study

“…In the absence of dynamics simulations, it is difficult to judge whether the system can overcome or even bypass the S 1 barrier and reach the intersection seam, which lies 29 kcal mol −1 below the Franck–Condon region and 18 kcal mol −1 below the S 1 minimum. There has been at least one report of a nonfluorescent chromophore that is capable of overcoming a similar barrier in excited‐state dynamics 46. At present, the internal conversion mechanism can thus only be regarded as a tentative explanation for the very short fluorescence lifetime of 1DFMN in YvtA‐LOV.…”

The effect of hydration on the photo-deactivation pathways of 4-aminopyrimidine

“…2a and 3a, see also Refs. [37,60]) two S 1 minima for the complex with two water molecules (see Figs. 2b and 3b) were obtained.…”

Gas-Phase IR Spectroscopy of Nucleobases

“…For 4-aminopyrimidine, surface hopping calculations identified two conical intersections (5,33,(80)(81)(82)(83)(84)(85)(86)(87)(88)(89)(90)(91)(92): deformation at the C2 position leads to deactivation of the excited state with a lifetime, τ*, of 1 ps and deformation at the C5=C6 bond with a τ* of 400 fs. Immobilizing the latter with a 5 membered ring forms adenine with a conical intersection due to the C2 deformation, τ* of 1 ps and dynamics similar to that in guanine.…”