Benign Decay vs. Photolysis in the Photophysics and Photochemistry of 5-Bromouracil. A Computational Study

Abstract

The excited state potential energy surface of 5-bromouracil has been studied with ab initio CASPT2//CASSCF calculations to rationalize the competition between the benign decay and the photolysis found experimentally. The surface is characterized by an extended region of degeneracy between S(1) and S(0). The access to this region has been studied with minimum energy path calculations from the FC structure, the seam of intersection has been mapped in detail, and the decay paths from different regions of the seam have been characterized. There are two decay paths with low barriers that are limiting cases for the actual decay dynamics. The first path involves the bromine elimination and leads to a region of near degeneracy between the ground and excited states, and the second one leads back to the reactant through a conical intersection between the two states. The conical intersection for benign decay is part of a seam that lies along the C(5)-Br stretching coordinate, and decay at the region of the seam with a stretched C(5)-Br bond leads to photolysis. Thus, the reactivity depends on the point of the seam at which decay to the ground state takes place. The low experimental photolysis quantum yield suggests that the energetically favored decay is the one that regenerates the reactant, while the low barriers computed to access the region of decay are in agreement with the measured picosecond excited state lifetime.

Quantum dynamics study of fulvene double bond photoisomerization: The role of intramolecular vibrational energy redistribution and excitation energy

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Electron Attachment to a Hydrated DNA Duplex: The Dinucleoside Phosphate Deoxyguanylyl‐3′,5′‐Deoxycytidine

“…[44][45][46][47][48][49][50][51][52][53][54][55][56][57] Recently, the electron affinities of thymine-adenine and guanine-cytosine base pairs stacking between different bases were studied by the resolution of identity MP2 (RI-MP2) approach. [58,59] As a crucial step in achieving a realistic description of electron attachment to nucleotide oligomers, dinucleoside phosphate deoxycytidylyl-3',5'-deoxyguanosine (dCpdG), dinucleoside phosphate deoxyguanylyl-3',5'-deoxycytidine (dGpdC), dinucleoside phosphate deoxythytidylyl-3',5'-de-…”

(β‐D‐Ribofuranosyl)formamidine in the Design and Synthesis of 2‐(β‐D‐Ribofuranosyl)pyrimidines, Including RF‐Containing Derivatives

“…In the calculations, a seam of intersection was found along a combination of the C 5 Br dissociation coordinate and the torsion coordinate around the C 5 C 6 bond. It was composed of segments with short and long CBr distances 126. Photolysis has a low quantum yield of up to 5 %,127 which indicates that the most favoured decay route to the ground state involves the segment with a short CBr distance.…”