The time-resolved thermal lensing measurements were carried out on 2-hydroxybenzophenone, pyridazine and benzene in acetonitrile at the 248 nm excitation in order to investigate the feasibility for the calorimetric standards on photothermal methods. The heat conversion efficiency values of 2-hydroxybenzophenone and pyridazine were estimated to be unity compared with that of benzene, revealing that 2-hydroxybenzophenone and pyridazine should show no fluorescence and no photochemical reactions. Therefore, these molecules should be good calorimetric standards at the 248 nm excitation. (C) 2003 Elsevier Science B.V. All rights reserved.