Study of Coumarin Fluorescent Probes by Electra-Optical and Laser Spectrofluorimetry Methods

摘要

Modified electro-optical absorption and emission methods were used to measure the dipole moments of six coumarin fluorescent probes (CU1, CU4, CU7, CU30, CU120, CU334) in the equilibrated ground, excited Franck-Condon and equilibrated excited states. The measurements were performed in cyclohexane and dioxane at room temperature. The equilibrated ground and excited states dipole moments measured by electro-optical methods are compared with those derived from other measurements techniques and from semiempirical calculations. Experiments and calculations performed in this work reveal a set of anomalous and interesting properties of CU7 and CU30 in solutions. The spectral dependence of some electro-optical coefficients and, consequently, dipole moments in excited Franck-Condon state indicates that the absorption band is a superposition of several (at least two) electronic transitions. Most probably there are two close-lying singlet electronic states which contribute to the first absorption band. Our electro-optical and laser spectrofluorimetry measurements do not support the formation of twisted intramolecular charge transfer (TICT) state after optical excitation in the studied coumarins, at least in cyclohexane and dioxane.