Synthesis, Crystal Structures, Linear and Nonlinear Optical Properties, and Theoretical Studies of (p‐R‐Phenyl)‐, (p‐R‐Phenylethynyl)‐, and (E)‐[2‐(p‐R‐Phenyl)ethenyl]dimesitylboranes and Related Compounds

Abstract

The (p-R-phenyl)dimesitylboranes (R=Me(2)N, MeO, MeS, Br, I), (p-R-phenylethynyl)dimesitylboranes (R=Me(2)N, MeO, MeS, H), (E)-[2-(p-R-phenyl)ethenyl]dimesitylboranes (R=Me(2)N, H(2)N, MeO, MeS, H, CN, NO(2)), (E)-[2-(2-thienyl)ethenyl]dimesitylborane, and (E)-[2-(o-carboranyl)ethenyl]dimesitylborane have been prepared through the reaction of the appropriate p-R-phenyl- and p-R-phenylethynyllithium reagents with dimesitylboron fluoride and by hydroboration of the appropriate p-R-phenylacetylene, 2-ethynylthiophene, and o-ethynylcarborane with dimesitylborane. Their UV/Vis absorption and emission spectra have been recorded in a range of solvents with the fluorescence maxima of the donor-substituted compounds in particular exhibiting large bathochromic shifts in highly polar solvents, indicative of charge transfer leading to large dipole moments in the excited state. The molecular structures of the (p-R-phenyl)dimesitylboranes (R=Me(2)N, MeO, MeS, Br, I), the (E)-[2-(p-R-phenyl)ethenyl]dimesitylboranes (R=Me(2)N, H(2)N MeO, MeS, H), (p-R-phenylethynyl)dimesitylborane (R=Me(2)N), and (E)-[2-(2-thienyl)ethenyl]dimesitylborane, which have been determined from single-crystal X-ray diffraction measurements, offer evidence of increased conjugation in the ground state with increased donor strength of the R substituent. Their first- and second-order molecular hyperpolarizabilities have been obtained from EFISH and THG measurements, the first-order hyperpolarizabilities being largest for the strongest R-substituent donors. AM1 calculations have been performed on these compounds, showing reasonable agreement with the experimentally obtained bond lengths and hyperpolarizabilities, as well as on several related hypothetical compounds containing multiple C==C bonds, most of which are proposed to have even larger hyperpolarizabilities.

Diazaborolyl-boryl push–pull systems with ethynylene–arylene bridges as ‘turn-on’ fluoride sensors

“…Compound 3 separated as colourless platelets (0.83 g, 90% yield). 1 H-NMR (C 6 D 6 ), δ = 1.20 (t, 3 Cyanophenylethynyl)-1,3-diethyl-1,3,2- 28, H 6.06, N 14.05; found C 75.66, H 6.38, N 13.73.…”

“…The residue (1.81 g, 95%) was identified by NMR spectroscopy and subsequently desilylated to give compound 11. 1 H-NMR (C 6 D 6 ): δ = 0.16 (s, 9H, SiMe 3 ), 2.15 (s, 12H, o-CH 3 -mesityl), 2.18 (s, 6H, p-CH 3 -mesityl), 6.76 (s, 4H, m-H-mesityl), 7.12 (d, 3 J HH = 1.9 Hz, 1H, H-thiophene), 7.13 (d, 3 J HH = 1.9 Hz, H-thiophene) ppm. 13 …”

“…Crystallization of the crude material from n-hexane yielded 0.58 g (54%) of product 12 as large colourless crystals. 1 H-NMR (C 6 D 6 ): δ = 1.14 (t, 3 29, H 7.25, N 5.30; found C 75.84, H 7.41, N 5.26. 2-Isopropylamino-1-bromobenzene (13): Molecular sieves (20 g, 3 Å) were added to a solution of 2-bromoaniline (15.0 g, 87.2 mol) in acetone (150 mL) and the resulting mixture was vigorously stirred for 24 h. It was filtered and the filtrate was evaporated to dryness to afford a yellow oil.…”

“…After removal of solvents the residue was purified by short path distillation (2x10 -5 bar, 60 °C bath temperature) to give 15.6 g (84%) of product 13 as colourless liquid. 1 H-NMR (C 6 D 6 ): δ = 0.88 (d, 3 …”

“…This field of research has been dominated by the use of the dimesitylboryl group (BMes 2 , Mes = 2,4,6-Me 3 C 6 H 2 ), in which the unsaturated boron centre is stabilized towards oxidation and hydrolysis by the steric shielding of the four orthomethyl groups. [2][3][4][5] The BMes 2 group is considered to have an acceptor strength between that of NO 2 -and CN-groups. 6,7 Such electron-deficient compounds are efficient electron-transporting and/or emitting layers in organic light emitting diodes (OLEDs).…”