Substituent effects on absorption and fluorescence spectra of carbostyrils

Absorption and fluorescence spectra as well as quantum yields of a series of differently substituted carbostyrils (quinolin-2(1H)-ones) are reported. Especially for compounds containing donor substituents in position 6, substantial bathochromic shifts (comparable to analogous coumarins) of both absorption as well as fluorescence transitions are obtained. High absorption intensities and quantum yields are found for 7-donor substituted isomers. Semiempirical molecular orbital calculations (AM1 for structures, ZINDO for electronic transition energies) prove to be a suitable tool for the prediction of absorption and fluorescence properties of these compounds. Ab initio and density functional calculations establish the lactam form as the dominant tautomer of the parent quinolin-2(1H)-one. (C) 1999 Elsevier Science B.V. All rights reserved.