TWISTED INTRAMOLECULAR CHARGE-TRANSFER BEHAVIOR OF A PRETWISTED MOLECULE, 4-BIPHENYLCARBOXYLATE BONDED TO POLY(METHYL METHACRYLATE)

A trace amount of 4-biphenylcarboxylate having a pre-twisted biphenyl moiety was attached to a poly(methyl methacrylate) side chain and the fluorescence properties of the chromophore were investigated in variou s solvents such as ethyl acetate and butyl chloride. At room temperatu re, the polymer exhibited a distinct red shift of the short wavelength emission (325 nm) and an enhanced emission intensity around 430 nm up on excitation at the absorption red edge. The temperature dependence o f the intensity ratio (R) of the 325 nm emission to the 430 nm emissio n was observed when exciting at the red edge over the temperature rang e between -20 and 60 degrees C. However, the temperature dependence wa s not observed when exciting at the shorter wavelength The Arrhenius p lot of the R value shows the activation energy of 6.0 kJ/mol which is in good agreement with the energy required for the twist of the biphen yl moiety. Together with the results of red edge excitation effects it was concluded that the pre-twisted geometry of the biphenyl moiety is preserved by the restriction of the polymer chain to facilitate the f ormation of the twisted intramolecular charge transfer (TICT) state up on excitation.