ICT based photoacid probe for microsolvation and H-bonding assisted proton transfer process from solute to solvents

Two AIE-active Schiff base fluorescent probes for highly selective recognition of Cu2+ ions

Two helical Schiff base compounds (H4TPA and H4TPE) containing a triphenylamine (TPA) or tetraphenylethylene (TPE) scaffold were successfully synthesized and characterized. Both H4TPA and H4TPE exhibited typical aggregation-induced emission characteristics in the mixed solvent of THF/H2O. The two compounds also showed high selectivity and sensitivity for the recognition of Cu2+ over other ions in THF/HEPES (1:4, V/V, pH = 7.4, 2.0 × 10-5 M), and could be used as turn-off fluorescent probes for Cu2+. The stoichiometric ratios and association constants were estimated via Job's plots and UV-vis spectra titration, and the detection limits of H4TPA and H4TPE toward Cu2+ were calculated to be 2.41 × 10-7 M and 1.38 × 10-7 M, respectively. Besides, the crystal structure of the complex obtained from the interaction of H4TPA with Cu2+ well illustrated the binding modes, which helped us understand the Cu2+ recognition mechanism of H4TPA and H4TPE. Moreover, the detection of Cu2+ and spiked recovery experiments were carried out, which indicated that the two probes can be applied to Cu2+ detection in real samples with satisfactory recoveries.

Photophysical properties of push-pull monocationic D-π-A+ thiophene based derivatives: Fluorosolvatochromism and pH studies

Photophysical properties of two thiophene salts of the form D-π-A⁺ are studied in several solvents and at various pH values of the aqueous solution. The studied compounds embrace methoxy group as electron donating moiety at one end and cationic amidine group with and without fluorine atom at the ortho position of the amidine group as the electron withdrawing group at the other end of the molecules and separated by thiophene ring. The two thiophene derivatives are 4-(5-(4-methoxyphenyl)thiophen-2-yl)benzamidine hydrochloride salt (MOTB) and 2-fluoro-4-(5-(4-methoxyphenyl) thiophen-2-yl)benzamidine hydrochloride salt (FMOTB). The observed changes in the fluorescence emission spectra with the nature of the solvent were found to be much more pronounced than the corresponding absorption spectra which signify an emission from the intramolecular charge transfer state. The higher bathochromic shift in the fluorescence emission spectra than the absorption spectra indicates that the excited state dipole moment is larger than that of the ground state. It has also been observed that the presence of the fluorine atom in the electron withdrawing part does not show any changes in the absorption spectra while a clear bathochromic shift is observed in the fluorescence emission spectra indicating an enhanced strength of the electron withdrawing ability in case of FMOTB. Effect of pH was also studied and pK_a values were evaluated. The observed photophysical properties were correlated to the normalized solvent polarity parameter (E_T^N) when solvents are classified to protic and aprotic solvents. This designates the importance of hydrogen bonding interactions. We have also applied a couple of linear solvation energy relationships for better understanding of the exact contribution of each solvent parameter on each photophysical property. We have found that both Catalán's and Laurence's treatments show that the photophysical properties are mainly controlled by the solvent's non-specific interactions. However, these models were not sufficient to interpret the observed data without the inclusion of the participation of the specific interactions.