J. Dey, J. L. Haynes, I. Warner
Mar 20, 1997
Citations
0
Influential Citations
28
Citations
Journal
Journal of Physical Chemistry A
Abstract
The absorption and fluorescence spectral characteristics of 9-acridinecarboxylic acid (9-ACA) and 9-(methoxycarbonyl)acridine (9-MCA) were studied in a series of organic solvents and in aqueous solutions. Fluorescence quantum yields ({Phi}{sub f}) and lifetimes ({tau}{sub f}) of the compounds were measured in these solvents. The absence of large Stokes-shifted emission in the case of 9-ACA and 9-MCA suggests the existence of a charge-transfer emitting state in 9-AA in which the carboxyl group is nearly coplanar with the aromatic ring. The {phi}{sub f} values for both compounds increase as a function of hydrogen-bonding capacity of the solvents. In near neutral to slightly acidic solutions, 9-ACA exists mainly in the zwitterionic form. Both 9-ACA and 9-MCA form monoprotonated species in moderately concentrated acid solutions. The acidium cation of 9-AA formed in the excited state in moderately concentrated acid solution reorganizes to produce a carbocation centered at the carbon atom of the carboxyl group. However, there was no indication of the formation of such acidium cations in the case of 9-ACA and 9-MCA even in concentrated perchloric acid medium. The pK{sub a}S of various prototropic equilibria involved in the group electronic state of the compounds were estimated. 42 refs., 8 figs., 2 tabs.