Interband optical transitions in DNA-like systems

The underlying band structure of the uniform DNA suggests the allowance of interband optical transitions. We consider such transitions in the uniform synthetic DNA, such as the poly(G)-poly(C) DNA, within a simple tight-binding model with a minimum set of parameters. We demonstrate that the helical conformation of the DNA strands results in unusual interband optical transitions all of which appear to be indirect in k space although the system has a direct band gap energy structure. Simple relationships of the optical gap and absorption linewidth to tight-binding model parameters are found. We study also the effect of disorder in base levels (relevant for the wet form of the DNA) on interband optical transitions