Synthesis and optical properties of organic-inorganic hybrid semi-interpenetrating polymer network gels containing polyfluorenes

Organic-inorganic hybrid semi-interpenetrating polymer network (semi-IPN) gels containing polyfluorenes (PFs) are synthesized by hydrosilylation reaction of joint and rod molecules in toluene, where PFs are poly(9,9-dihexylfluorene-2, 7-diyl) (PF6) or, poly(9,9-dioctylfluorene-2,7-diyl) (PF8), joint molecules are 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS), or 1,3,5,7,9,11,13,15- octakis(dimethylsilyloxy)pentacyclo-[9,5,1,1,1,1]octasilsesquioxane (POSS), and rod molecules are 1,5-hexadiene (HD) or 1,9-decadiene (DD). The semi-IPN gels containing low molecular weight PF6 show higher photoluminescence efficiency (φ_g) than the toluene solution of PF6L (φ_s). The semi-IPN gels composed of long rod molecule of DD and cubic joint molecule of POSS show the most effective increase in the emission intensity. The emission intensity of PF6L increases as formation of the network in the POSS-DD semi-IPN gel. The POSS-DD semi-IPN gels containing high molecular weight PF6 and PF8 also show the increase of emission intensity than those of the toluene solutions. The semi-IPN synthesized in cyclohexane show syneresis and phase separation between network structure and PF chains. The semi-IPN gels containing PF8 show emission peaks at 450 and 470 nm derived from β-sheet structure of PF8. A systematic study clears correlation between emission property and network structure and/or composition of semi-IPN gels. The semi-IPN gels provide emissive self-standing soft materials with high efficiency and in a narrow wavelength range emission.