Abstract: In this paper the Huckel molecular orbital theory has been applied to calculate ,the electronic energy level of a series of symmetrical and unsymmetrical oxacarbocyainine, benzimidazolooxacarbocyanine and quinoline-thiacyanine dyes. Their excitation energy, polarographic half-wave potential and spectral sensitization on silver halide emulsions were measured. The agreement between the calculated and observed values is proved to be fairly good.