The reaction of the N-lithiated 3,6-di-tert-butyl-carbazole (2) with 2-bromo-1,3-diethyl-1,3,2-benzodiazaborole (1a) and 2-bromo-1,3-diphenyl-1,3,2-benzodiazaborole (1b) afforded the 2-N-carbazolyl-functionalized benzodiazaboroles 3a and 3b as colourless solids in 77 and 73 % yield, respectively. Synthesis of 2[5Ј-N-carbazolyl-2Ј-thienyl]-1,3-diethyl-1,3,2-benzodiazaborole (5a) was effected by lithiation of N-(2-thienyl)carbazole (4) and subsequent reaction with equimolar amounts of 1a, and 5a was obtained in 68 % yield. Similarly,

A series of diphenylacetylenes with one 1,3,2-benzodiazaborolyl end group (BDB) and a second end group X (X = H, OMe, NMe(2), SMe, CN and BDB) were synthesized using established 1,3,2-benzodiazaborole methodologies. The 1,3,2-benzodiazaborolyldiphenylacetylenes with X = p-H (4), p-OMe (5), p-NMe(2) (6), p-SMe (7) and p-CN (8) end groups are functionalized with cyano groups at the central ring in an ortho-position to the triple bond. Molecular structures of 2, 3, 5, 6 and 7 were determined by X-ray diffraction. These borylated systems show intense blue luminescence in cyclohexane, toluene, chloroform, dichloromethane and tetrahydrofuran, whereas green luminescence was observed in acetonitrile solutions. Thereby Stokes shifts in the range 1700-8600 cm(-1) and quantum yields of 0.60-1.00 were observed in cyclohexane solutions. The absorption maxima (308-380 nm) are well reproduced by TD-DFT computations (B3LYP/G-311G(d,p)) and arise from strong HOMO-LUMO transitions. The LUMOs in all the molecules under study are mainly located on the diphenylacetylene bridge, while with the exception of the dimethylamino derivative 6, the HOMO is largely benzodiazaborolyl in character. Thus, the S1←S0 absorption bands are assigned to π(diazaborolyl)-π*(diphenylacetylene) transitions. In contrast to this, in compound 6 the HOMO is mainly represented by the terminal dimethylaminophenyl unit. While calculated ground state dipole moments μ(g) are small (1.1-7.5 D), experimentally determined changes of the dipole moments upon excitation are large (14.8-19.7 D) and reflect a significant charge transfer upon excitation. NLO activities of the rod-structured compounds 2, 4, 6 and 8 are indicated by calculated static first-order hyperpolarizabilities β up to 76.8 × 10(-30) esu.

Gas-phase He I photoelectron spectra of a series of 2-arylethynyl-1,3,2-benzodiazaboroles BEP-X [1 (X = H), 2 (X = Me), 3 (X = OMe), 4 (X = SMe), 5 (X = NMe2), 6 (X = Br)] have been recorded and assessed by density functional theory calculations. The first ionization energies of these benzodiazaboroles are in the order 5 (7.0 eV) < 3 (7.15 eV) < 2 (7.2 eV) < 1 = 4 = 6 (7.3 eV). As an important result of this study it was disclosed that in contrast to the remaining diazaboroles the frontier orbitals of the amino derivative 5 lack contributions from the diazaborole part of the molecule. In keeping with this, the dipole moment of the ground state (5.51 D) is only slightly changed, to 6.60 D, upon electronic excitation. This also rationalizes the low Stokes shift of 2600 cm−1 in comparison to the other diazaboroles in this study (5900−7300 cm−1).