Theoretical study of electronic spectra and photophysics of uracil derivatives.

The changes that the UV absorption spectrum and the photophysics of uracil undergo under hydrogen substitution or deprotonation, were studied theoretically within the CS-INDO/CI scheme. First of all this method was tested on uracil. It was then used for the calculation of the electronic structure of excited states (Sn, Tn) of a large number of uracil derivatives (1-, 3- and 5-methyluracil; 1,3-, 1,5- and 3,5-dimethyluracil; 5-fluoro- and 5-chlorouracil), including some anions (1- and 3-methyluracil anion). The excited states were obtained in the singly-excited configuration interaction approximation (S-CI) and the correlation effects on (pi pi*) states were studied by including the most important doubly- and triply-excited configurations in the CI. The S-CI wavefunctions were used for the calculation of the most important electronic matrix elements for spin-orbit coupling. The photophysics of these compounds is discussed using Jablonski diagrams