Twisted Intramolecular Charge-Transfer Phenomenon as a Fluorescence Probe of Microenvironment: Effect of Polymer Concentration on Local Viscosity and Microscopic Polarity around a Polymer Chain of Poly(methyl methacrylate)

A 4-(N,N-dimethylamino)benzoate group showing a twisted intramolecular charge transfer (TICT) was bonded to a poly (methyl methacrylate) side chain and the effects of polymer environment on fluorescence were investigated in ethyl acetate. The temperature dependence of the fluorescence behavior indicated restricted side chain rotation and reduced solvation in the polymer even under dilute conditions. With increasing polymer concentration, the TICT emission showed a blue-shift and decreased intensity up to a polymer concentration of 70%. Above this concentration, the activation energy to form the TICT state suddenly increased. The twisting motion of the dimethylamino group required a free volume of 5.4 cm³/mol, which was in good agreement with the activation volume obtained from pressure effects on the TICT phenomenon. The TICT phenomenon is shown to be sensitive to both local polarity and local viscosity of the surroundings so that the TICT chromophore is expected to be a candidate for a fluorescence probe in polymer property studies.