Lewis Acidic Borane Adducts of Pyridines and Stilbazoles for Nonlinear Optics

Abstract

A series of neutral pyridyl adducts involving the strong Lewis acids BF3 and B(C6F5)3 has been prepared, and their second-order nonlinear optical coefficients (EFISH method) have been examined. The formation of the pyridyl−boron bond leads to enhancement of the dipole moments and second-order NLO coefficients (β and β(0)). Reactions of DMAP (4-Me2N−C5H4N) with BH3, BF3, and B(C6F5)3 give the corresponding neutral pyridine adducts DMAP·BH3 (orthorhombic, Pbca, a = 9.6914(7) Å; b = 11.7173(9) Å; c = 22.718(2) Å; V = 1622.4(5) Å3; Z = 8; p = 1.114 g cm-3), DMAP·BF3 (orthorhombic, Pbca, a = 10.430(3) Å; b = 8.111(2) Å; c = 20.295(7) Å; V = 1717.0(9) Å3; Z = 8; p = 1.470 g cm-3), and DMAP·B(C6F5)3 (orthorhombic, Pbca, a = 12.322(1) Å; b = 20.556(2) Å; c = 28.455(3) Å; V = 7207.4(14) Å3; Z = 8; p = 1.508 g cm-3). Reactions of Me2N−4-C6H4−CHCH−C5H4N, MeO−4-C6H4−CHCH−C5H4N, and Me2N−4-C6H4−C⋮C−C5H4N with BF3 and B(C6F5)3 result in materials that are highly luminescent and incorporate structural features that are known to give rise to large second-order NLO effects. X-ray diffraction analysis for the compound Me2N−4-C6H4−C⋮C−C5H4N·B(C6F5)3 (monclinic, P21/c, a = 9.883(2) Å; b = 10.717(1) Å; c = 28.421(4) Å; β = 91.96(1)°; V = 2993.4(8) Å3; Z = 4; p = 1.629 g cm-3) is also described.