Synthesis and third-order nonlinear optical studies of a novel four-coordinated organoboron derivative and a bidentate ligand: The effect of the N → B coordinative bond

The third-order nonlinear optical characterization of a new boronate (2) derived from 4-dimethylaminocinnamaldehyde was performed by third-harmonic generation (THG) at the infrared wavelength of 1550 nm. Compound 2 was prepared from the reaction of diphenylboronic acid and the bidentate ligand (1) and characterization was made through UV, IR, 1H, 11B, and 13C NMR and X-ray diffraction. The THG experiments showed that the N → B coordinative bond in 2 enhanced the second molecular hyperpolarizability of the type γ(3)(−3ω, ω, ω, ω) by a factor of three with respect to the value exhibited by the ligand 1. On the other hand, Z-scan studies at 800 nm (femtosecond (fs) pulses) also showed that such coordinative bond increased the nonlinear absorption (two-photon absorption (TPA)) in 2 with respect to 1. These studies demonstrate that the N → B coordinative bond facilitates the polarization of the electronic π-system, a situation that optimizes the third-order NLO response. Results on the excited state absorptions in these compounds are also presented.