New alternative copolymers of thiophene and benzimidazole with alkyl side chains (alkyl = n-C5H11, n-C7H12, n-C10H21, n-C12H25, and n-C18H37) have been prepared. The polymerization by Stille coupling of 2-alkyl-4,7-dibromobenzimidazoles with 2,5-bis(trimethylstannyl)thiophene gave the corresponding copolymers in good yields. The new copolymers showed absorption and photoluminescence peaks at about 436-460 and 520-530 nm, respectively. Quantum yields of the photoluminescence were about 21-37 in DMF. Addition of NaOH led to a red-shift of the absorption peak by about 60 nm. Their XRD patterns showed a diffraction peak in a low angle region (Bragg spacing d(1) = 17.4-35.4 Angstrom) and a broad peak at about d(2) = 4.0 Angstrom. Plots of the d(1) space vs. the number of carbon atom in the alkyl side chain gave a linear line with a slope of 1.35 Angstrom per carbon, suggesting an end-to-end type packing of the copolymer in the solid. References: 35
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