Dye probes of nanoclusters in liquids

Calculations have been carried out to optimize the structure of Van der Waals complexes of methanol with N-methyl-2-nitroaniline, a dye capable of shifts in visible and ultraviolet spectra that depend on (1) solvent dielectric, (2) solvent shell structure, and (3) hydrogen bonding to a slight extent. Hartree-Fock-Roothaan calculations with various basis sets and single-excitation configuration interaction (SCI) are compared to Density Functional-Theory Time-Dependent Hartree-Fock (DFT-TD) results for three low-energy ultraviolet electronic transitions. Energy-minimized structures are reported for a trimeric complex of two methanol-one water as found using a 6-311G** basis indicating two possible hydrogen-bonding schemes. The effect of a dielectric medium on the ultraviolet spectrum is compared to gas-phase clusters. Electronic transitions are also given for the dye-probe complexed with four or five methanol molecules finding good agreement with observed shifts in the ultraviolet spectrum as found with the TDI I F-DFT formalism for the lowest energy transition near 425 nm.