Adsorption and electronic states of morin on TiO2 nanoparticles

- Assemblies of morin molecules on TiO2 were investigated and compared with free morin.
- Stark effect spectroscopy was used to estimate the electrooptical parameters.
- The excited state shows no significant charge-transfer character.
- The electronic structure of adsorbed morin corresponds to the anion form.

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, Δμ, and in polarizability, Δα, between the ground and excited state were determined. Adsorption causes an increase in both Δμ and Δα of morin but the vector Δμ 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.