Effects of the hydrogen bonding on the fluorescence of ketone-substituted poly(phenylene)s in solutions and solid state

The fluorescence intensities of poly(2-benzoyl-1,4-phenylene) (PBP) and pol y(2-trifluoroacetyl-1,4-phenylene) (PTFAP) in chloroform and dioxane soluti ons were found to decrease on addition of phenols. The fluorescence intensi ty diminishes in proportion to the acidity of phenols. Similar phenomena we re observed on addition of acetic acid and a fluorinated alcohol. However, when the poly(p-vinylphenol) (PVPh) was added to these polymer solutions, t he fluorescence intensity increased with an increasing amount of PVPh. Thes e results suggest that hydrogen bonding between the carbonyl group of PBP o r PTFAP and the OH group of phenols has opposite effects on fluorescence in the two cases. The strong hydrogen bonding with small phenol compounds in the excited state may increase the restriction of the bond rotation between the phenyl rings of the polymer and result in decreasing of T-electron con jugation and the fluorescence intensity. On PVPh addition to the polymer so lution, the PVPh chain may wrap around PBP or PTFAP via hydrogen-bonding fo rmation and reduce polymer chain associations, thereby mitigating the conce ntration quenching effect and conferring a large position contribution to t he fluorescence intensity. PTFAP-PVPh blend films were prepared. Among thes e blends, 1 wt % of PTFAP in PVPh showed the highest fluorescence emission intensity 80 times larger than that of the pure PTFAP film. This suggests t hat the PTFAP chains are dispersed molecularly, or nearly so, in a matrix o f PVPh in the 1 wt % blend; consequently, each polymer chain contributes ad ditively to the emission intensity with a minimal deleterious impact due to aggregation.