Influence of Polymer Side Chains on the Adjacent Microenvironment: A Fluorescence Probe Study by Means of Twisted Intramolecular Charge-Transfer Phenomena

Copolymers of ω-((4-(N,N-dimethylamino)benzoyl)oxy)dodecyl methacrylate were prepared using a large excess of an alkyl methacrylate where the alkyl group is methyl, butyl, cyclohexyl, or dodecyl. The content of the (dimethylamino)benzoate (DMAB) group, a fluorescence probe in the copolymer, is less than 0.04%. The dual-fluorescence spectra of polymer samples were studied in dilute solutions. The intensity ratio (R) of emission from the twisted intramolecular charge-transfer (TICT) state (a* band) to that from the planar non-CT excited state (b* band) provided useful information on the effect of a neighboring side chain on the twisting motion of the DMAB chromophore. The R value decreases with increasing bulkiness of the neighboring side chains. Excitation wavelength dependence of R indicates that there is a certain conformational distribution of DMAB already in the ground state. When the bulkiness of the neighboring side chain increases, the distribution becomes broader and the red-edge excitation effect on R becomes more prominent. These neighboring side chain effects on the twisting mobility of DMAB group are also dependent on polymer/solvent combinations.