A series of rigid poly(p-phenylene ethynylene)s (PPE1-PPE4) with biphenyl-(M1-M3) and phenyl-(M4) side groups is prepared from appropriately functionalized monomers. Herein, the solution and solid state absorption studies show the polymers have adopted twisted and rigid conformations, as supported by deep HOMO energy levels (25.76 to 25.81 eV). The absorption maxima of PPE1-PPE3 are shifted to shorter wavelength (lambda(max) = 375-381 nm) as compared to linear poly(p-phenylene ethynylene)s (446 nm), implying a nonplanar conformation. The self-assembly of polymers into fibers is examined using scanning electron microscopy. The fibers are not observed in PPE4 with short phenyl side group, suggesting the important role of the interplay between rigidity, position, and size of the side chains toward the formation of fibers. (C) 2016 Wiley Periodicals, Inc.