Adsorption and electronic states of morin on TiO2 nanoparticles

Low temperature Stark effect spectroscopy has been used to investigate the changes in the electronic charge distribution in the flavonoid morin caused by adsorption to colloidal TiO2 nanoparticles in ethanol. The differences in the permanent dipole moment, Delta mu, and in polarizability, Delta alpha, between the ground and excited state were determined. Adsorption causes an increase in both Delta mu and Delta alpha of morin but the vector Delta mu remains nearly perpendicular to the Ti-dye direction, like in the free molecule. This picture of electron movement on electronic excitation is supported by semiempirical calculations. In contrast to other dyes adsorbed on TiO2, it indicates the indirect effect of chelated Ti atom on morin electronic structure which does not involve the atomic orbitals of the metal, and the electronic structure of adsorbed morin similar to that of the anion. (C) 2014 Elsevier B.V. All rights reserved.