We have conducted here a theoretical exploration, discussing the distinct excited state lifetimes reported experimentally for the two lowest lying protonated isomers of uracil. In this regard, the first-principal computational levels as well as the nonadiabatic surface hopping dynamics have been employed. It has been revealed that relaxation of the 1 ππ* state of enol−enol form (EE + ) to the ground is barrier-free via out-of-plane coordinates, resulting in an ultrashort S 1 lifetime of this species. For the second most stable isomer (EK + ), however, a significant barrier predicted in the CASPT2 S 1 potential energy profile along the twisting coordinate has been proposed to explain the relevant long lifetime reported experimentally.
Ab initio and surface-hopping non-adiabatic dynamics simulation methods have been employed to investigate the relaxation mechanisms in protonated thymine (TH+) and cytosine (CH+). A few conical intersections have been located...
Quantum chemical computational method as well as the adiabatic dynamics simulation have been employed to investigate the non-radiative relaxation mechanism of protonated 9H- and 7H-adenine (AH+). We have located three...
In this work, different levels of quantum computational
models
such as MP2, ADC(2), CASSCF/CASPT2, and DFT/TD-DFT have been employed
to investigate the photophysics and photostability of a mycosporine
system, mycosporine glycine (MyG). First of all, a molecular mechanics
approach based on the Monte Carlo conformational search has been employed
to investigate the possible geometry structures of MyG. Then, comprehensive
studies on the electronic excited states and deactivation mechanism
have been conducted on the most stable conformer. The first optically
bright electronic transition responsible for the UV absorption of
MyG has been assigned as the S2 (1ππ*)
owing to the large oscillator strength (0.450). The first excited
electronic state (S1) has been assigned as an optically
dark (1nπ*) state. From the nonadiabatic dynamics
simulation model, we propose that the initial population in the S2 (1ππ*) state transfers to the S1 state in under 100 fs, through an S2/S1 conical intersection (CI). The barrierless S1 potential
energy curves then drive the excited system to the S1/S0 CI. This latter CI provides a significant route for ultrafast
deactivation of the system to the ground state via internal conversion.
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