This paper deals with UV-induced ds (ss)-DNA damage, placed in buffer solution and in wet, dry absorbed layer, using optical spectroscopy and conductivity methods. Mechanisms of UV induced ds (ss)-DNA damage are accounted of photochemical reactions of cyclobutane-pyrimidine dimer and (4-6) adduct formation. These models are based on: decreasing absorption intensity with maxima at 252 nm for ds-DNA and 256 nm for ss-DNA water solutions, and long-wave shifting of absorption maximum (252 nm) for ds-DNA water solution. The absorption spectral range of 235 < λ < 252 nm is defined by absorption on T and A bases. Photoluminescence spectra of wet ds-DNA layer have maxima at 432,440 and 454, 463 nm before and after UV irradiation of 337 nm and 365 nm for one hour respectively.

The photochemical reactions appear by decreasing dry absorbed ds-DNA molecular layer with networks conductivity under periodically switched UV irradiation. As a result the conductivity decreases after the first radiation reflecting the reducing of pyrimidine bases (that formed dimers) and the contribution to ds-DNA conductivity. The increasing of conductivity after UV irradiation could be caused by a particular reparation of ds-DNA under applied voltage of 1 V. But it's important to develop methods for the further ability to direct possible photochemical reactions in ds (ss)-DNA.