UV excitation and radiationless deactivation of imidazole

Abstract

The vertical spectrum and the radiationless decay of imidazole have been investigated theoretically. Benchmark calculations were performed employing different methods and levels. Four different conical intersections were characterized and the reaction paths connecting the Franck-Condon region to them were computed. Two of the conical intersections show puckered structures while the other two show NH and ring dissociation patterns. The pipi( *)/S(0) N(1)-puckered conical intersection is connected to the planar pisigma( *)/S(0) ring-opened conical intersection by a branch of the crossing seam. After excitation into the first (1)pipi( *) state, the internal conversion can occur either in this branch of crossing seam or along the NH-dissociation path.

Ultrafast Dynamics of UV‐Excited Imidazole

“…Table 2 reports selected results for the TZVP + mod basis set together with the root mean square deviation (RMSD) between the present theoretical results and the experimental results of Devine et al [39] using the fitted values reported in reference [27] In contrast to the results obtained for pyrrole, [23] the B3LYP functional is in better agreement with experimental values than the PBE0 functional. The functional with the largest fraction of Hartree-Fock (HF) exchange contribution (BHLYP) provides the worst results.…”

“…[33] Altogether, this means that TDDFT may not work well to describe the excited-state dynamics of some molecules and that excitedstate dynamics with TDDFT must always be preceded by an extensive check of the potential-energy surfaces. In the case of imidazole, the validity of TDDFT for studying its excited-state dynamics has been assured by the good comparison between TDDFT and ab initio multireference configuration interaction (MRCI) dynamics performed for pyrrole [23,34] and by comparative investigation of reaction pathways of imidazole computed with different methods, presented here and in reference [27]. However, as we shall discuss below, the TDDFT method proved to be inadequate for investigating crossing to the ground state, which is quite an important restriction.…”

“…[26] Four conical intersections between the first excited and ground states have been previously described for imidazole. [27] In structural terms, they are characterized by NH dissociation, CN dissociation, N puckering, and NH puckering. [27] In particular, the NH-and CNdissociation conical intersections are connected by the same branch of crossing seam.…”

“…[27] In structural terms, they are characterized by NH dissociation, CN dissociation, N puckering, and NH puckering. [27] In particular, the NH-and CNdissociation conical intersections are connected by the same branch of crossing seam. [27] Here, we combine theoretical nonadiabatic dynamics simulations and experimental time-resolved photoelectron spectroscopy (TRPES), both in the gas phase, to discuss how each conical intersection contributes to the internal conversion, depending on the initial excitation energy.…”

Molecular Photofragmentation Dynamics in the Gas and Condensed Phases

“…Indeed, such photo-induced ring-openings have now been explored theoretically in several heterocyclic systems, including furan, [117][118][119] pyrrole, 120 imidazole, 121 2-aminooxazole, 122 adenine, 123 spiropyran, 124,125 and -glucose.…”