Computation the Effective Dielectric Constant of Nano-Probe Local Surrounding by Solvatochromic Spectral Shift Measurement of Organic Dye Molecule

Computer modeling the dielectric properties of the cucurbit [7]uril (CB [7]) cavity based on the Onsager-Liptay model was carried out by analyzing the solvatochromic shift of the absorption spectrum of 1-(3ammoniumpropyl) -4-[(E) -2-(3,4-dimethoxyphenyl) ethynyl]pyridinium upon the formation of the inclusion complex with CB [7] in a water solution. The CB [7] cavity was considered as a polar environment into which the dye chromophore is placed. Positions of the maxima of the dye absorption spectra were measured experimentally in the following solvents: methanol, ethanol, i-propanol, n-butanol and water with known dielectric and optical properties. These values were used for parametrization of the Onsager-Liptay equation. Quantum-chemical calculations were used to determine molecular structures, dipole moments of the ground and excited states, and polarizability of the dye. Theoretical value of the effective dielectric permittivity of the cavity is in good agreement with the literature data derived by another method. Thus, we propose a new method for investigation the dielectric constant both in bulk liquids and in very small liquid volumes, for example, into picoliter droplets.