A series of dithia[3.3]paracyclophane-fluorene copolymers 1a-c and 3-5 were synthesized by a palladium-catalyzed reaction between 9,9-di-n-hexylfluorene-2,7-bis(trimethylene boronate) and the corresponding dithiacyclophane precursors. The transannular pi-pi interaction in the dithiaparacyclophane modified the electronic and optical properties of the copolymers significantly, resulting in emission red shifts relative to a reference polymer 2. The observed shift in 1a and 5 was accompanied by enhanced photoluminescence (PL) efficiency, whereas that in 1b, 1c, 3, and 4 experienced a significant to nearly complete fluorescence quenching. The quenching effect is likely to involve an electron-transfer process and could be correlated qualitatively to the reduction potential of the "external" aromatic moiety in the cyclophane unit.