Two-photon absorption resonance in 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP)

A two-photon absorption spectrum of 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) in tetrahydrofuran solution has been studied by the Kerr ellipsometry technique. The spectral shape and amplitude of the imaginary part of the dominant molecular hyperpolarizability term Im(γXXXX) is compared with the relevant linear absorption spectrum within a simple two-level model. Agreement between the measured γXXXX=2.0×10−48 m5 V−2 and calculated γXXXX=(1.2–1.5)×10−48 m5 V−2 two-photon absorption molecular hyperpolarizabilties in the vicinity of the two-photon resonance transition is satisfactory.