Long-Wavelength-Absorbing and -Emitting Carbostyrils with High Fluorescence Quantum Yields

Synthesis, absorption and fluorescence spectra, as well as quantum yields of a series of donor-acceptor-substituted carbostyrils (=quinolin-2(1H)-ones), are reported. Unprecedented strong absorption maxima (ε=10000 – 20000) close to the visible spectrum, large Stokes shifts up to 130 nm, and quantum yields up to 0.7 are obtained with derivatives containing donor substituents at C(6) and C(7), and either one Ph substituent at C(3) or one CF₃ residue at C(4). For analytical applications in biochemistry and medicine, N(1)-functionalization, or amidoacylation at C(3) in the case of the CF₃ derivatives, is possible without a concomitant hypsochromic shift of their absorption and emission maxima. Semiempirical molecular-orbital calculations (AM1 for structures, ZINDO for electronic transition energies) prove to be a suitable tool for the prediction of absorption properties of these compounds. The crystal-structure analysis of 6,7-dimethoxy-1-methyl-3-nitro-4-(trifluoromethyl)quinolin-2-(1H)-one ( 7 ) (C₁₃H₁₁F₃N₂O₅, monoclinic, P2₁/c, a=12.372(2), b=12.154(2), c=10.119(2)Å, β=112.95(2)°) shows that the NO₂ group, squeezed between the CF₃ and the C=O group, is oriented almost perpendicularly (87.8(4)°) to the ring plane. The intramolecular F???N distance between the CF₃ and the NO₂ group is only 2.513(4)Å.