Three coordinate phosphorus and boron as π-donor and π-acceptor moieties respectively, in conjugated organic molecules for nonlinear optics: crystal and molecular structures of E-Ph–CHCH–B(mes)2, E-4-MeO–C6H4–CHCH-B(mes)2, and E-Ph2P–CHCH–B(mes)2[mes = 2,4,6-Me3C6H2]

Abstract

Hydroboration of π-donor substituted alkynes D–CC–H [D = Ph₂P, 4-X–C₆H₄-(X = H, MeS, MeO, H₂N), and (η⁵-C₅H₅)Fe(η⁵-C₅H₄-)] with dimesitylborane {[(mes)₂BH]₂, mes = 2,4,6-Me₃C₆H₂} yields air-stable ‘push–pull’E-alkenes of the form E-D–CHCH–B(mes)₂, which possess large molecular hyperpolarizabilities, β, as shown by electric-field induced second-harmonic generation (EFISH) experiments at 1.91 µm; single crystal X-ray diffraction studies indicate that E-Ph–CHCH–B(mes)₂ and E-4-MeO–C₆H₄–CHCH–B(mes)₂ crystallise in centrosymmetric space groups, whereas E-Ph₂P–CHCH–B(mes)₂ crystallises in the acentric space group P2₁2₁2₁ and exhibits powder SHG of 1.064 µm laser light.