Herein we report the synthesis and characterization of a new series of styryl-based push-pull dyes containing a free amino group and their Schiff base derivatives. The dyes include the dicyanomethylene group as an acceptor and different para-substituted alkylamines as donors. Morever as a proton-sensitive group a pyridin-2-yl substituent was attached to the para-position of the phenyl moiety in both series of compounds. The photophysical properties of the dyes were examined in various solvents with different polarities and showed absorption in the visible region and green-red emission with low quantum yields. The absorption and the emission maxima were shifted bathocromically by increasing the solvent’s polarity. However, there was no correlation with the polarity parameters of the solvents. The pH-sensitive properties of all prepared Schiff bases were examined against TBAOH in DMSO, via deprotonation of the OH group in the salicylidene moiety and their reverse protonation was also investigated using TFA. The Schiff bases exhibited a bathochromic shift upon the addition of TBAOH to their solutions in DMSO. Therefore, they showed potential to be utilized as colorimetric and luminescence pH sensors. The second-order nonlinear optical (NLO) responses of the dyes were measured by the electric field-induced second harmonic (EFISH) generation method. The highest μβ values were obtained for the dyes bearing the julolidine donor as 1430 × 10−48 esu (for free amino derivative) and 1950 × 10−48 esu (for Schiff base derivative), respectively. The structural and electronic properties of the dyes as well as their NLO properties were further studied using DFT calculations. The thermal stabilities of all dyes were evaluated by thermogravimetric analysis (TGA). The TGA data showed that all dyes were thermally stable up to 250 °C.

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In this manuscript, we have successfully synthesized and characterized a new series of styryl based push-pull dyes containing free amino group and their Schiff bases derivatives in which dicyanomethylene was used as the acceptor group and different para-substituted alkylamines as the donor groups and 2-pyridyl as proton sensitive group. All compounds showed absorption in the visible region and green-red emission with low quantum yields. The photophysical properties were examined in various solvents with different polarities. The absorption and emission maxima were shifted bathocromically by increasing solvents polarity however, there was no regular correlation with polarity parameter. Significant red shifts were observed in the absorption and fluorescence emission maxima on increasing the electron-donating ability of the substituents. The observed color changes were photographed naked eyes and under illuminating UV-lamp. The pH sensitive properties of newly prepared Schiff bases against TBAOH were examined inside DMSO, furthermore their reserve protonation were also investigated using TFA. The structural and electronic properties of all newly synthesized compounds were studied using DFT calculation. In addition, NLO property of compounds were investigated by DFT. For determination thermal properties of all compounds were investigated and they showed good thermal stability up to 250 oC by TGA analyses under inert atmosphere. Our results indicate that the styryl based new push-pull dyes are promising candidate materials for NLO and pH applications.