UV Absorption Spectrumof Alternating DNA Duplexes.Analysis of Excitonic and Charge Transfer Interactions.

A detailed investigation of the excited states accessedby UV absorptionin alternating DNA duplexes was performed by means of an extensivesampling of intra- and intermolecular degrees of freedom. The excitedstates were computed using the algebraic diagrammatic constructionmethod to second-order (ADC(2)). A realistic DNA environment was includedthrough an electrostatic embedding QM/MM coupling scheme. The resultsindicate that (i) most excited states are delocalized over at mosttwo bases, (ii) charge transfer states are located at higher energiesthan the bright states in the Franck–Condon region, but (iii)coupling between locally excited and charge transfer states may providea route to dynamical charge separation, and (iv) spectral broadeningis mainly caused by intramolecular vibrations. [ABSTRACT FROM AUTHOR]