Theoretical investigation on the fast kinetics mechanism for vibronically activated photochromism in benzopyrans. The role of the conical intersection topology in driving the mode enhanced photoproducts

Breaking the Kasha Rule for More Efficient Photochemistry

“…Last but not least, it is worth noting that, in the studies of some photochromic reactions, an increase of the quantum yield at the short-wavelength excitation was attributed to increased reactivity from the “hot” vibrational levels of the S 1 state but not from the S n state (see section ). However, based on these experimental results, it is extremely difficult to differentiate between these pathways, especially in view of ultrafast S n ↔S 1 m transitions forming conical intersections (see section ) through which the nuclear coordinates may change drastically …”

Deep in blue with green chemistry: influence of solvent and chain length on the behaviour of N- and N,N′- alkyl indigo derivatives

“…By using Hessians along this IRC path we identified possible reactive normal modes, parallel to the IRC, that could correspond to the branching space of the CI and, along them, minimized Δ E = E (S 1 ) − E (S 0 ) until a predefined threshold of 0.05 eV (or less) was observed. 50,51…”

Nonadiabatic molecular dynamics simulations for ultrafast photo-induced ring-opening and isomerization reactions of 2,2-diphenyl-2H-chromene

“…Following studies for spirobenzopyran, 40,41 DPC can also have two nearly isoenergetic CF conformations of DPC-T and DPC-C isomers due to pyran ring inversion, however, only one of them was considered in previous theoretical investigations. 29–32 In the present study, we consider both of them and define the C-type (T-type) isomer as the pyran ring bending to the left (right)-hand side as shown in Fig. 1.…”

“…Theoretical studies for the photochemical mechanisms of chromenes are relatively limited and the adopted models are usually truncated. 29–32 Celani et al 29 performed CASSCF calculations for the parent benzopyran and a ring-opening reaction coordinate on the S 1 state is proposed as a transition state connecting the CF intermediate with the acyclic S 1 /S 0 conical intersection (CI). Migani et al 30 carried out combined CASPT2//CASSCF calculations for the parent and 2,2-diethyl-2 H -chromene and proposed the same photochromic mechanism as that of Celani et al 29 Furthermore, the energy profile along the S 1 state ring-opening reaction coordinate was refined with the inclusion of a dynamic correlation energy.…”

“…The conversion from the more stable ring-puckered conformation to the planar form is required to activate the ring-opening process. Galvão 32 reported a CR-EOMCCSD(T)//CIS study on benzopyran with both CF and CC intermediates optimized on the S 1 state and suggested the internal conversion may occur earlier when approaching CI along reaction path. Besides these truncated models, Chuev et al 35 explored the ground and first excited state pyran-ring opening mechanism of 2 H -pyridochromene derivatives utilizing the semi-empirical PM3 method with a multielectron configuration interaction.…”