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2-(p-N,N-dimethylaminostyryl)benzoxazole (OS), 2-(p-N,N-dimethylaminostyryl)-benzothiazole (SS) and 2-(p-N,N-dimethylaminostyryl)naphtiazole (PS) were prepared and their absorption and fluorescence spectra were measured in various solvents at room temperature. On the basis of the solvatochromic behavior the ground state (mu(g)) and excited state (mu(e)) dipole moments of these pN,N-dimethylaminostyryl derivatives were evaluated. The dipole moments (mu(g) and mu(e)) were estimated from solvatochromic shifts of absorption and fluorescence spectra as function of the dielectric constant (epsilon) and refractive index (n) of applied solvents. The absorption spectra only slightly are affected by the solvent polarity in contrast to the fluorescence spectra that are highly solvatochromic and display a large Stokes shift. The analysis of the solvatochromic behavior of the fluorescence spectra as function of Deltaf (epsilon, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment change along with the strongly red-shifted fluorescence, as the solvent polarity is increased, demonstrate the formation of an intramolecular charge transfer state (ICT). Compounds under the study were used as fluorescence probes for monitoring the kinetics of polymerization. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate (MMA) and during photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA).

Fluorescence from the initially excited singlet state (LE) and the twisted intramolecular charge-transfer (TICT) state of 4-(N,N-dimethylamino)benzoate (DMAB), 4-(N,N-diethylamino)benzoate (DEAB), 4-(N-pyrrolidino)benzoate (PYR), 4-(N-piperidino)benzoate (PIP), 4-(N-morpholino)benzoate (MOR), and 4-(N-2,6-dimethylmorpholino)benzoate (26DMM) were compared with the free and polystyrenebound chromophores. The ground-state twisting of the donor with respect to the acceptor can have a large influence on the charge distribution. The polymeric chain can force a less planar geometry and cause a bathochromic shift and a broadening of the absorption band in the electronic absorption spectra. In the area of 350 nm the emission is assigned to the locally excited state (with a planar geometry) and the emission with λ Fl max in the area of 450-520 nm to the TICT state (with a perpendicular conformation). Experimental results show (i) no polymeric chain effect in emission distribution for the DMAB molecule, (ii) a significant red edge effect (REE) for the PIP probe, (iii) a slight red edge effect for 26DMM, (iv) a specific blue edge effect (BEE) for PYR probe, and (v) a combination of REE and BEE for MOR. Adaptation of Grabowski's TICT hypothesis allows one to calculate the activation energy of TICT state formation, the backreaction TICT f LE, and the thermally activated TICT fluorescence. The polymeric chain essentially does not change the activation energy (E 1) for the thermally activated TICT state formation, indicating that the polymeric chain does not change the microscopic viscosity in the range affecting measurable changes in the TICT-LE equilibrium. The polymeric chain increases the gap between the lowest forbidden ν0 vibrational state and less forbidden ν1 vibrational state by 195-225 cm -1 (0.6-2.4 kJ mol -1 ). Experimental results suggest that the polymer chain affects only the vibrational relaxation of tested molecules without any significant effect on the thermodynamics of the TICT and LE states equilibrium.