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.

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.

Investigation of two-photon absorption behavior in symmetrical acceptor-pi-acceptor derivatives with dimesitylboryl end-groups. Evidence of new engineering routes for TPA/transparency trade-off optimization.

Investigations of the non-linear optical properties of a novel series of A-pi-A quadrupoles, based on dimesitylboron end-groups, reveal the promising potential of elongated vinylboranes derivatives for combined enhanced two-photon absorption cross-section and improved transparency in the visible region. In addition, the excited state lifetime can be significantly enhanced in A-pi-A'-pi-A derivatives. This opens a new route towards optimized molecules for optical power limiting.

Two contrasting ethynyl hydroboration pathways in the formation of a novel tris-hydroboration product from reaction of dimesitylborane with 2,5-diethynylpyridine.

Reaction of 2,5-diethynylpyridine with dimesitylborane, [(Mes)(2)BH](2)(Mes = mesityl = 2,4,6-Me(3)C(6)H(2)), gave the unexpected tris-hydroboration product 1-[(Mes)(2)B]-2-[Z-1-[(Mes)(2)B]ethylidene]-5-[E-[(Mes)(2)B]vinyl]-1,2-dihydropyridine, which has been structurally characterised by single-crystal X-ray diffraction.

Boron chemistry lights the way: optical properties of molecular and polymeric systems.

Electrooptical and electronic materials are the subject of much research interest, whereby the focus has often been on electron-rich organic molecules. In the past years, new routes to electron-deficient systems have been developed that take advantage of the fact that three-coordinate boron is isoelectronic and isostructural with a positively charged carbocation, which allows neutral, p-type materials to be synthesized directly. This minireview summarizes recent work on compounds with 3- and 4-coordinate boron as well as boron clusters, placing it in the context of prior studies by the research groups of Williams and Glowgowski, Kaim, Lequan, and Marder.