Two new fluorescent ethenyl- and ethynyl-dimesitylboranes functionalized with a dansyl group 1 and 2 have been synthesized in good yields. Compound 1 was prepared by the hydroboration of 5-(dimethylamino)-N-(prop-2-ynyl)naphthalene-1-sulfonamide I with dimesitylborane (HB(Mes)₂) in dry tetrahydrofuran at room temperature, and compound 2 was synthesized by Pd-catalyzed cross-coupling of I with 4-I-C₆H₄B(Mes)₂. Both organoborane compounds 1 and 2 have been characterized by infrared spectroscopy, NMR spectroscopy, and mass spectrometry. The molecular structures of I and 1 were confirmed by X-ray crystallography. The electronic absorption and redox properties of 1 and 2 were investigated. They both exhibit large positive solvatochromism and their emission spectra have been recorded in a range of organic solvents with the fluorescence maxima exhibiting large bathochromic shifts in highly polar solvents, indicative of charge transfer which leads to large dipole moments in the excited state. The application of 1 as a blue fluorescent dopant in doped guest–host organic light-emitting diodes is also described.