The D-π-A-π-D molecules studied here are comprised of carbazole (Cz) donor units, phenylene (Ph) ring π bridges, and the acceptor core (BDT or AQ). These molecules have a significant degree of conformational flexibility because rotation is possible around the carbazole-phenyl bonds and the phenyl-core bonds. This gives rise to four independent dihedral angles, denoted as θ 1 /θ 1 and θ 2 /θ 2 (see Fig. ). To restrict the associated number of conform-ers, we will consider only molecules of C 2 symmetry (θ 1 = θ 1 ,