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 ωB97XD 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 (α_av), first hyperpolarizability (β_av) and global reactivity descriptors e.g., chemical hardness (η), electrophilicity index (ω) along the proton transfer co-ordinate are in conformity with the respective optimum principles. Maximum value of β_av is found in the case of nitro substituted pyrazole derivative. Variation of β_av along the proton transfer co-ordinate for all compounds have been correlated with the variation of Δµf₀/(S₁-S₀)³ using two-level approximation and electronic special extent (<R²>) along the proton transfer coordinate.