We have synthesized new-type of pentacene copolymers containing linear-and branched-dialkoxylphenyldiethynylene units via a modified Sonogashira coupling reaction at room temperature to prepare low-band gap polymers (< 1.7 eV). The structures of polymers were confirmed by H-1 NMR and the molecular weights were determined by size exclusion chromatography. The electrochemical and optical properties of the polymers were studied using cyclic voltammetry and UV-vis absorption to estimate the HOMO and LUMO levels as well as their optical bandgaps. Branch-type pentacene copolymer 2 exhibited good solubility in common organic solvents as well as good film-forming ability, while linear-type polymer 1 has poor solubility owing to stronger interaction between polymer chains. Notably, in terms of optical stability, our pentacene copolymers exhibit much better stability in solution than TIPS-ethynyl substituted pentacene (TIPSEP).