Abstract: The ultraviolet spectra of organic iron-sulfur cluster complexes in dichloromethane in the range of 190-400 nm have been studied. It was found that the ultraviolet absorption peaks (λ_max)of these compounds showed noticeable bathochromic shifts due to π-π^*transition with increasing the solution concentration. But the compounds containing isolated C-Sbond or C=Obond did not show such shifts. We also studied some π-π or n-π conjugated compounds and discovered that their ultraviolet obsorption peaks (λ_max) showed bathochromic and hypsochromic shifts due to π-π^*and n-π^*transion, respectively, with increasing the solution concentration.

Key words: Ultraviolet spectra, Concentration effects, π-π^*transition, n-π^*transition