Fluorescence Properties of Derivatives of Anthroic Acids

摘要

Fluorescence behaviour of 9-anthracenecarboxylic acid (H-ANCOOH),10-bromoan-thracene-9-carboxylic acid (Br-ANCOOH) and 10-cyanoanthracene-9-carboxylic acid (CN-ANCOOH) in solvents of different polarities was investigated,using the steady state and time-resolved methods.The dual fluorescence of the acids originates clearly from the fluorescence of the undissociated acids and the anions.From the ground-state absorptiometric titration the pK_a values have been obtained,whereas for the values of pK_a in the excited singlet state (pK_a) the Forster cycle was used.Introduction of the electron withdrawing groups (Br and CN) shifts the pK_a values both in the ground and singlet excited states to the lower values compared to the parent molecule.On the other hand,the presence of the electron accepting groups in anthracene moiety influences the spectral position of the bimolecular exciplexes (excited state complexes) formed between the excited acids and the electron donor molecule,such as p-cyano,N,N-dimethylaniline (DMABN) in nonpolar solvents.A correlation between the decreasing pK_a values in the excited singlet state and the position of the charge transfer luminescence of the intermolecular exciplexes has been found.