Computation of electrical responsive properties and global reactivity descriptors along the proton transfer co-ordinate of donor–acceptor substituted pyrazole derivatives

Ground and excited-state proton transfer and electrical responsive properties along the proton transfer co-ordinate of four donor–acceptor substituted pyrazole derivatives have been investigated using the density function-based range separated hybrid GGA functional <i>ω</i>B97XD with 6-311G(d) basis. Both intrinsic reaction coordinate (IRC) and distinguished co-ordinate (variation of O–H distance of the enol tautomer) have been chosen as a proton transfer co-ordinate of the titled compounds for comparison. Our study reveals that the various electrical responsive parameters like average polarizability (<i>α</i>_av), first hyperpolarizability (<i>β</i>_av) and global reactivity descriptors e.g., chemical hardness (<i>η</i>), electrophilicity index (<i>ω</i>) along the proton transfer co-ordinate are in conformity with the respective optimum principles. Maximum value of <i>β</i>_av is found in the case of nitro substituted pyrazole derivative. Variation of <i>β</i>_av along the proton transfer co-ordinate for all compounds have been correlated with the variation of Δ<i>µf</i>₀/(<i>S</i>₁-<i>S</i>₀)³ using two-level approximation and electronic special extent (&lt;<i>R</i>²&gt;) along the proton transfer coordinate.