Donor-acceptor conjugated polymers containing a new imide-functionalized naphthodithiophene (INDT) as the acceptor unit and a 2,2'-bithiophene with varied substituents as the donor unit have been synthesized. The bandgaps of these polymers depend strongly on the dihedral angle of the 2,2'-bithiophene unit. The 3,3'-dialkoxy substitution (polymers PDOR/PBOR) leads to near planar bithiophene conformation due to the well-known S-O short contact, while the 3,3'-dialkyl substitution (polymer PDR) results in significant twisting due to the steric effect. Consequently PDOR/PBOR shows the lowest bandgap of 1.82/1.85 eV while PDR has a bandgap of 2.38 eV. Bulk-heterojunction solar cells of the polymer/fullerene blends have been fabricated. Preliminary results show that PBOR gives the best device performance with power conversion efficiencies as high as 2.45% in air without any thermal annealing treatment, indicating the promising potential of INDT-containing conjugated polymers for efficient solar cells. (C) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3818-3828