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

• Published in: Chemistry : a European journal 2006-03, Vol.12 (10), p.2758-2771
• Main Authors: Yuan, Zheng, Entwistle, Christopher D., Collings, Jonathan C., Albesa-Jové, David, Batsanov, Andrei S., Howard, Judith A. K., Taylor, Nicholas J., Kaiser, Hanns Martin, Kaufmann, Dieter E., Poon, Suk-Yue, Wong, Wai-Yeung, Jardin, Christophe, Fathallah, Sofiane, Boucekkine, Abdou, Halet, Jean-François, Marder, Todd B.
• Format: Article
• Language: English
• Subjects: boranes; Chemical Sciences; Inorganic chemistry; nonlinear optics; or physical chemistry; semiempirical calculations; synthetic methods; Theoretical and; X-ray diffraction
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200501096

The (p‐R‐phenyl)dimesitylboranes (R=Me2N, MeO, MeS, Br, I), (p‐R‐phenylethynyl)dimesitylboranes (R=Me2N, MeO, MeS, H), (E)‐[2‐(p‐R‐phenyl)ethenyl]dimesitylboranes (R=Me2N, H2N, MeO, MeS, H, CN, NO2), (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=Me2N, MeO, MeS, Br, I), the (E)‐[2‐(p‐R‐phenyl)ethenyl]dimesitylboranes (R=Me2N, H2N MeO, MeS, H), (p‐R‐phenylethynyl)dimesitylborane (R=Me2N), 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. Increased conjugation in the ground state accompanies increased donor strength of the R substituent (see picture): This is evidenced from single‐crystal X‐ray diffraction measurements of the molecular structures of the (p‐R‐phenyl)dimesitylboranes (R=Me2N, MeS, Br, I), the (E)‐[2‐(p‐R‐phenyl)ethenyl]dimesitylboranes (R=Me2N, H2N MeO, MeS, H), (p‐R‐phenylethynyl)dimesitylborane (R=Me2N), and (E)‐[2‐(2‐thienyl)ethenyl]dimesitylborane.