A study of the relationship between the chemical structures and the fluorescence quantum yields of coumarins, quinoxalinones and benzoxazinones for the development of sensitive fluorescent derivatization reagents

To develop new fluorescent derivatization reagents, we investigated the relationship between the chemical structures and the fluorescence quantum yields (Phi(f)) of coumarins, quinoxalinones and benzoxadinones. Forty-six compounds were synthesized and their fluorescence spectra were measured in n-hexane, ethyl acetate, methanol and water. The energy levels of these compounds were calculated by combination of the semi-empirical AM1 and INDO/S (CI = all) methods. The DeltaE(T-n(n,pi*), S-1(pi,pi*)) (the energy gap between the T-n(n,pi*) and S-1(pi,pi*) states) values were well correlated with the 0, values, which enables us to predict the Phi(f) values from their chemical structures. Based on this relationship, 3-phenyl-7-N-piperazinoquinoxalin-2(1H)-one (PQ-Pz) and 7-(3-(S)-aminopyrrolidin-1-yl)-3-phenylquinoxalin-2-(IH)-one (PQ-APy) were developed as fluorescent derivatization reagents for carboxylic acids. The derivatives of the carboxylic acids with PQ-Pz and PQ-APy showed large Phi(f) values even in polar solvents, suggesting that these reagents are suitable for the microanalysis of biologically important carboxylic acids by reversed phase HPLC.