A novel series of soluble alternating conjugated copolymers, comprised of 9.9-dihexylfluorene and cyclopentadithiophenes (P1-P5), were synthesized via Pd-catalyzed Suzuki coupling reaction in good yields. The UV-vis absorption spectra, fluorescence spectra, fluorescence quantum yields, and cyclic voltammograms of P1-P5 are also reported. The P2 and P3 with electron-donating non-pi-substituents (ethylenedioxy and propylenedioxy bridges the 3,3-positions of the thiophene groups) display high fluorescence quantum yields and red-shifted absorption as compared with nonsubstituted P1. However, the P4 and P5 are weakly fluorescent and exhibit blue-shifted absorption which are due to the presence of electron-withdrawing pi-substituents (carbonyl and dicyanoethenyl). The behavior of P4 and P5 can be attributed to the significant electronic coupling between the pi-substituents and the conjugated polymer backbone that leads to a less allowed optical transition between the ground and the lowest excited state, resembling the meta conjugation effect in phenylene-derived conjugated pi-systems. This argument is supported by molecular orbital distribution calculations.