We have studied the dependence of intersystem crossing and the spatial extent of singlet and triplet excitons in platinum-containing poly-yne polymers with the general formula [Pt(PR3)(2)=C=CLC=C](n) (R = Et, Bu-n; L = pyridine, phenylene, or thiophene) as a function of electron delocalization in the spacer group L. We also report the synthesis route of those compounds. The optical absorption, photoluminescence, and photoinduced absorption of the corresponding polymers and monomers have been measured. We find that conjugation is increased but intersystem crossing is reduced by the electron-rich thiophene unit, while the opposite occurs for the electron-deficient pyridine unit as compared to the phenylene unit. For all investigated systems, we find that the singlet excited state and a higher lying T-n triplet excited state extend over more than a repeat unit while the T-1 triplet state remains localized to less then one repeat unit.