HeI spectra of some thienyl polyenic thienyl ketones I (m, n = 0, 0; 1, 0; 2, 0; 1, 1) are reported. The assignment of the spectra have also been done using the optimized MNDO MO calculation on each studied mol. The linear reduction of HOMO potential energy (Ip) which is mainly antibonding character of ethylenic group with the increment of ethylenic group no. is the base of homologous linear rule of this series compounds The lack of conjugative bond in whole mol. system could be considered as separation of carbonyl group.

Key words: CONJUGATION, QUANTUM CHEMISTRY, PHOTOELECTRON SPECTROSCOPY, THIOPHENE P, THIENONE