Optical absorption of bisphenol A based pyrazoloquinoline dimers

The paper presents the measured absorption spectra for several newly synthesized derivatives of bisphenol A based pyrazoloquinoline dimers (BAPQD). The experimental results are compared with quantum chemical calculations performed by semiempirical method AM1 and PM3. Molecular mechanic analysis shows that BAPQD dyes possess by a large number of equilibrium molecular conformations with similar total energies and small energy barriers between these states; thus at room temperature (T=300 K) the molecular dynamics exhibits slow temporal evolution passing a large number of intermediate slightly non-equilibrium conformational states. For this reason the semiempirical quantum chemical methods have been combined with the molecular dynamics simulations. The semiempirical PM3 method exhibits the best agreement with the experimental data, especially in the prediction of the spectral position of the first absorption band (absorption threshold). Taking into account that such good agreement is found for a set of more complex organic systems like BAPQD this may be of substantial interest for chemical engineering which deals with the designing of new efficient organic luminophores for electroluminescent applications.