Side-chain effects on the morphology and properties of fluorene-based alternating copolymers

Soluble fluorene-based alternating copolymers containing benzene as the comonomer were synthesized and characterized, in which three different side chains (hydrogen atom, linear octyloxy and bulky benzyloxy groups) were attached to the phenylene ring. The effect of the side chains with different steric hindrances on the photophysical, thermal and electrochemical properties as well as the morphology were investigated. Moreover, the chain conformation and spectroscopic properties in dilute solution were studied to understand the solvent effect. Aliphatic and aromatic solvents were demonstrated to have different influences on the spectra of the polymers owing to various interaction mechanisms in the excited states. Also, a significant decrease of up to 80 degrees C in the thermal degradation temperature was observed as a result of the introduction of large benzyloxy units. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the polymers were estimated to be -5.76 to -5.82 eV and -2.19 to -2.27 eV, respectively, from cyclic voltammetry measurements. In addition, the electronic structures of the polymers were described via quantum chemical calculations. (c) 2007 Society of Chemical Industry.