Heterocyclic azole nonlinear optical chromophores. 1. Donor-acceptor substituted pyrazole derivatives

We have described the synthesis of a variety of 1,3,1,4, and 1,5 donor-acceptor conjugation extended substituted pyrazole derivatives and have studied their spectr6scopic and nonlinear optical properties. These materials are thermally stable and absorb strongly in the UV-visible, albeit at much shorter wavelengths than comparably substituted cyclic azapolyenes such as 2-pyrazolines. Quadratic hyperpolarizability measurements suggest that the pyrazoles are significantly nonlinear, and that 1,3 and 1,4 substitution is preferred. 1,5 substitution causes significant drop in the nonlinearity and a blue shift in the long-wavelength absorption maximum, presumably due to a twisting and partial deconjugation of the substituents to relieve unfavorable steric interactions. The experimental results are compared with those predicted by simple “finite field” computational procedures.