Exciton States in Synthetic Polynucleotides

Singlet exciton states double stranded homopolynucleotides and copolynucleotides are determined within the framework of Frenkel exciton model taking into account the effect of configuration mixing between different exciton states. Interbase interactions are taken into account up to the distance of the order of 15 Å and they are calculated directly using the generalized charge densities in the base pairs previously obtained by the authors. The exciton states of model DNA is also discussed in which two kinds of base pairs are arranged in random order. Generally the oscillator strength associated with the lowest exciton states decreases by the effect of configuration mixing. There can be found no weak π→π ^* transition near 280 mµ in poly (A–U) and copoly \(\left(\begin{array}{c}\text{U--A}\\ \text{A--U}\end{array}\right)\). In a model DNA the absorption intensity in the long wave length side of the main absorption band depends linearly on G–C content.