Photochemical Ring-Opening Reaction of 1,3-Cyclohexadiene: Identifying the True Reactive State

Abstract

The photochemically induced ring-opening isomerization reaction of 1,3-cyclohexadiene to 1,3,5-hexatriene is a textbook example of a pericyclic reaction and has been amply investigated with advanced spectroscopic techniques. The main open question has been the identification of the single reactive state which drives the process. The generally accepted description of the isomerization pathway starts with a valence excitation to the lowest lying bright state, followed by a passage through a conical intersection to the lowest lying doubly excited state, and finally a branching between either the return to the ground state of the cyclic molecule or the actual ring-opening reaction leading to the open-chain isomer. Here, in a joint experimental and computational effort, we demonstrate that the evolution of the excitation−deexcitation process is much more complex than that usually described. In particular, we show that an initially highlying electronic state smoothly decreasing in energy along the reaction path plays a key role in the ring-opening reaction.

Compensation States Approach in the Hybrid Diabatization Scheme: Extension to Multidimensional Data and Properties

“…Very strong changes of the adiabatic states could require to use unreasonably large diabatic state spaces within the model because the diabatic states are usually defined at a single reference point. This problem showed up in our work for phenyl iodide but can also be found in other recent studies . The problem is solved by the use of so-called compensation states recently introduced by us in ref .…”

Automatic Clustering of Excited-State Trajectories: Application to Photoexcited Dynamics

“…The ring-opening of CHD to HT is a prototypical Woodward–Hoffmann electrocyclic reaction, − which has been the subject of extensive theoretical and experimental studies. ,,− Following excitation to the S 1 (1B) electronic state, the wave packet rapidly accelerates out of the Franck–Condon region, with the conrotatory twist of the terminal carbon atoms already taking place before the 2A/1B conical intersection (CoIn) is reached. , The lifetime of the 1B state is on the order of 30 fs, , as indicated by the clear maxima in S 2 population in Figure . At the 2A/1B CoIn, the wave packet bypasses a cusp between the surfaces, forcing it to break symmetry via a set of symmetry equivalent 2A/1A CoIns. ,− The acceleration from the slope of the cusp region results in rapid decay to the ground S 0 state, forming either HT (initially cZc-HT) or returning to vibrationally hot CHD.…”

“…The ring-opening of CHD to HT is a prototypical Woodward–Hoffmann electrocyclic reaction, 38 − 40 which has been the subject of extensive theoretical and experimental studies. 30 , 37 , 41 − 64 Following excitation to the S 1 (1B) electronic state, the wave packet rapidly accelerates out of the Franck–Condon region, with the conrotatory twist of the terminal carbon atoms already taking place before the 2A/1B conical intersection (CoIn) is reached. 46 , 49 The lifetime of the 1B state is on the order of 30 fs, 55 , 59 as indicated by the clear maxima in S 2 population in Figure 2 .…”

Generalized Semiclassical Ehrenfest Method: A Route to Wave Function-Free Photochemistry and Nonadiabatic Dynamics with Only Potential Energies and Gradients

“…c Electronic EOM is propagated with local diabatization algorithm. ZN-TSH b , 204 MS-CASPT2 0.40 68 FS-TSH 205 XMS-CASPT2 N/A 68 ZN-TSH b , 206 SA-CASSCF 0.47 120 FS-TSH-EDC 207 XMS-CASPT2 0.47 89 EF-TSH c , 208 REKS d 0.36 277 FS-TSH 209 XMS-CASPT2 <0.5 <125 FS-TSH 210 TDA-TDDFT e 0.65 81 AIMS 211 α-SA-CASSCF 212 ∼0.5 139 κCSDM 198 XMS-CASPT2 0.40 117 Quantum (2D) 213 In practice, one sometimes approximates the overlap integral. Reference151 also provides a direct comparison between κTDCs, analytic TDCs computed from eq 18, and overlap-based TDCs computed in three different ways approximated from eq 91.…”