Significant role of the DNA backbone in mediating the transition origin of electronic excitations of B-DNA – implication from long range corrected TDDFT and quantified NTO analysis

摘要: We systematically investigate the possible complex transition origin of electronic excitations giant molecular systems by using recently proposed QNTO analysis [J.-H. Li, J.-D. Chai, G. Y. Guo and M. Hayashi, Chem. Phys. Lett., 2011, 514, 362.] combined with long-range corrected TDDFT calculations. Thymine (Thy) related a B-DNA biomolecule are then studied as examples, where model have been constructed extracting from perfect or an X-ray crystal (PDB code 3BSE) structure at least one Thy included. In first part, we consider composed core segment (e.g. Thy, di-Thy) surrounding physical/chemical environment interest backbone, adjacent stacking nucleobases) in gas phase examine how excitation properties vary response to environment. find that orbitals contributed DNA backbone nucleobases often participate Thy-related affecting their composition, absorption energy, oscillator strength. A vast number strongly backbone-orbital involved also found wavelength below ∼180 nm predicted TD-ωB97X. second take into account geometrically induced variation various segments, e.g. di-Thy, dTpdT etc., obtained different sources (ideal 3BSE). It is several these segments sensitive slight conformational variations, suggesting thermal motions may time exhibit very photo-induced physical and/or chemical processes.