Can the symmetrical Dewar pyridine be observed experimentally? A theoretical study

• Published in: Molecular physics 2020-04, Vol.118 (7), p.e1662126
• Main Authors: Varras, Panayiotis C., Gritzapis, Panagiotis S.
• Format: Article
• Language: English
• Subjects: CASMP2; CASSCF; conical intersection (CoIn); Deactivation; Dewar pyridine; Ground state; intersystem crossing (ISC); Ionization potentials; Perturbation theory; Potential energy; Self consistent fields; symmetrical Dewar pyridine
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268976.2019.1662126

In this work we study the possibility of the photochemical formation of the symmetrical Dewar pyridine (1-azabicyclo-[2,2,0]-hexa-2,5-diene), by applying the complete active space self-consistent field method and the multiconfigurational second-order perturbation theory to explore the corresponding ground and excited state potential energy surfaces. According to our theoretical calculations there are three possible paths that can be followed, one is a biphotonic process which involves irradiating pyridine in its ground state with a 358 nm laser guiding the system to an intersystem crossing S 1 /T 1 /S 0 of triple character whereby deactivation to the ground state, S 0 , Dewar minimum occurs, the second one, which is a ground state thermal reaction involves the use of a far-Infra-Red laser where planar pyridine is vibrationally excited to a very high vibrational level whose energy is comparable to that of the ground state transition structure, S 0 (TS), connecting the symmetrical S 0 Dewar pyridine and the ground state of planar pyridine. The third process is also a biphotonic one involving excitation of planar pyridine with an energy which is in the limits of its ionisation potential. In this case there is a theoretically accessible S 1 /S 0 Conical Intersection which leads directly to the ground state of the symmetrical Dewar pyridine.