Multiple Decay Mechanisms and 2D‐UV Spectroscopic Fingerprints of Singlet Excited Solvated Adenine‐Uracil Monophosphate. Issue 22 (26th April 2016)

• Record Type: Journal Article
• Authors: Li, Quansong; Giussani, Angelo; Segarra‐Martí, Javier; Nenov, Artur; Rivalta, Ivan; Voityuk, Alexander A.; Mukamel, Shaul; Roca‐Sanjuán, Daniel; Garavelli, Marco; Blancafort, Lluís
• Is Part Of: Chemistry. Volume 22:Issue 22(2016)
• Page Start: 7497
• Page End: 7507
• Publication Date: 2016-04-26
• Subjects: ab initio calculations -- DNA -- molecular electronics -- photophysics -- UV/Vis spectroscopy; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201505086
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The decay channels of singlet excited adenine uracil monophosphate (ApU) in water are studied with CASPT2//CASSCF:MM potential energy calculations and simulation of the 2D‐UV spectroscopic fingerprints with the aim of elucidating the role of the different electronic states of the stacked conformer in the excited state dynamics. The adenine 1 La state can decay without a barrier to a conical intersection with the ground state. In contrast, the adenine 1 Lb and uracil S(U) states have minima that are separated from the intersections by sizeable barriers. Depending on the backbone conformation, the CT state can undergo inter‐base hydrogen transfer and decay to the ground state through a conical intersection, or it can yield a long‐lived minimum stabilized by a hydrogen bond between the two ribose rings. This suggests that the 1 Lb, S(U) and CT states of the stacked conformer may all contribute to the experimental lifetimes of 18 and 240 ps. We have also simulated the time evolution of the 2D‐UV spectra and provide the specific fingerprint of each species in a recommended probe window between 25 000 and 38 000 cm −1 in which decongested, clearly distinguishable spectra can be obtained. This is expected to allow the mechanistic scenarios to be discerned in the near future with the help of the corresponding experiments. Our results reveal the complexity of the photophysics of the relatively small ApU system, and the potential of 2D‐UV spectroscopy to disentangle the photophysics of multichromophoric systems. Abstract : 2D‐UV fingerprints : Calculations of the excited state decay channels of the adenine uracil monophosphate (ApU) dinucleoside show that several species may contribute to the lifetimes measured experimentally. Simulations of the 2D‐UV spectra provide specific fingerprints for each state that will help to discern the mechanistic scenarios (see figure).