Multiphoton Control of 6π Photocyclization via State-Dependent Reactant–Product Correlations

Abstract

Multiphoton excitation promises opportunities for opening new photochemical reaction pathways and controlling photoproduct distributions. We demonstrate photonic control of the 6π photocyclization of ortho-terphenyl to make 4a,4b-dihydrotriphenylene (DHT). Using pump–repump–probe spectroscopy we show that 1 + 1′ excitation to a high-lying reactant electronic state generates a metastable species characterized by a red absorption feature that accompanies a repump-induced depletion in the one-photon trans-dihydro product (trans-DHT); signatures of the new photoproduct are clearer for a structural analogue of the reactant that is sterically inhibited against one-photon cyclization. Quantum-chemical computations support assignment of this species to cis-DHT, which is accessible photochemically along a disrotatory coordinate from high-lying electronic states reached by 1 + 1′ excitation. We use time-resolved spectroscopy to track photochemical dynamics producing cis-DHT. In total, we demonstrate that selective multiphoton excitation opens a new photoreaction channel in these photocyclizing reactants by taking advantage of state-dependent correlations between reactant and product electronic states.

Quadratic Unitary Coupled-Cluster Singles and Doubles Scheme: Efficient Implementation, Benchmark Study, and Formulation of an Extended Version

“…As an example for calculations of larger molecules, we have performed qUCCSD calculations for the S 0 → S 1 vertical transition energies of the cis - and trans -4 a ,4 b- dihydrotriphenylene (C 18 H 14 , see Figure ) using 6-31G* and 6-31+G* basis sets − as well as the aug-cc-pVDZ basis set for C and the cc-pVDZ basis set for H, , deonted as the “aVDZ” basis in the following discussions. These two excitation energies have been measured and used in recent experimental study that identifies these two molecules as products of 6π photocyclization of o -terphenyl through two distinct photochemical reaction pathways . We have also carried out EOM-CCSD and EOM-CCSD­(T)­(a)* calculations for comparison.…”

“…We have also carried out EOM-CCSD and EOM-CCSD­(T)­(a)* calculations for comparison. The ground-state structures obtained from density-functional theory calculations in ref have been used in these calculations.…”

“…These two excitation energies have been measured and used in recent experimental study that identifies these two molecules as products of 6π photocyclization of oterphenyl through two distinct photochemical reaction pathways. 135 We have also carried out EOM-CCSD 16 and EOM-CCSD(T)(a)* 147 calculations for comparison. The groundstate structures obtained from density-functional theory calculations in ref 135 have been used in these calculations.…”

“…The theory and details about the implementation are presented in Sections and . To demonstrate the usefulness of the new implementation, we report benchmark calculations for excitation energies in the “QUEST #1” benchmark set developed by Loos et al , as well as calculations of S 0 → S 1 vertical transition energies for cis - and trans -4 a ,4 b -dihydrotriphenylene (C 18 H 14 ) of interest to study of photocyclization of o -terphenyl . The computational details are presented in Section with the accuracy and limitation of the qUCCSD scheme discussed in Section and .…”

“…To demonstrate the usefulness of the new implementation, we report benchmark calculations for excitation energies in the "QUEST #1" benchmark set developed by Loos et al 133,134 as well as calculations of S 0 → S 1 vertical transition energies for cis-and trans-4a,4b-dihydrotriphenylene (C 18 H 14 ) of interest to study of photocyclization of oterphenyl. 135 The computational details are presented in Section 2.3 with the accuracy and limitation of the qUCCSD scheme discussed in Section 3.1 and 3.2. Finally, in Section 3.3, we discuss the formulation for an extended version of the qUCCSD (e-qUCCSD) scheme and a noniterative triples correction aiming to develop a UCC scheme with excitation energies correct up to fourth order, before closing the paper with a summary and an outlook in Section 4.…”