The solvent effect on the absorption spectra of coumarin 120 (C120) in water was studied utilizing the combined quantum mechanical∕molecular mechanical (QM∕MM) method. In molecular dynamics (MD) simulation, a new sampling scheme was introduced to provide enough samples for both solute and solvent molecules to obtain the average physical properties of the molecules in solution. We sampled the structure of the solute and solvent molecules separately. First, we executed a QM∕MM MD simulation, where we sampled the solute molecule in solution. Next, we chose random solute structures from this simulation and performed classical MD simulation for each chosen solute structure with its geometry fixed. This new scheme allowed us to sample the solute molecule quantum mechanically and sample many solvent structures classically. Excitation energy calculations using the selected samples were carried out by the generalized multiconfigurational perturbation theory. We succeeded in constructing the absorption spectra and realizing the red shift of the absorption spectra found in polar solvents. To understand the motion of C120 in water, we carried out principal component analysis and found that the motion of the methyl group made the largest contribution and the motion of the amino group the second largest. The solvent effect on the absorption spectrum was studied by decomposing it in two components: the effect from the distortion of the solute molecule and the field effect from the solvent molecules. The solvent effect from the solvent molecules shows large contribution to the solvent shift of the peak of the absorption spectrum, while the solvent effect from the solute molecule shows no contribution. The solvent effect from the solute molecule mainly contributes to the broadening of the absorption spectrum. In the solvent effect, the variation in C-C bond length has the largest contribution on the absorption spectrum from the solute molecule. For the solvent effect on the absorption spectrum from the solvent molecules, the solvent structure around the amino group of C120 plays the key role.

The aim of this study was to determine the presence of Asian dust particles (ADP) in patients suffering from conjunctivitis and its correlation with clinical scores for conjunctivitis. Forty-five patients from the Fukuoka area who were newly diagnosed acute conjunctivitis were selected. The degrees of inflammatory reaction, itchy sensation, hyperemia, eye discharge, and foreign body sensation were clinically recorded and scored. Eyes were washed with physiological solution. Solid particles collected from the washing solution were observed using a scanning electron microscope. Of the 45 samples, 44 were positive for the elements silicon (Si) and aluminum (Al), which are components of ambient Asian dust. Higher conjunctivitis scores were found in the subgroup in which the Asian dust/whole particle ratio was greater than average. This is the first apparent report on the correlation between amount of ADP exposure at the ocular surface and severity of ocular symptoms.

Excited states of three 7-aminocoumarin derivatives, coumarin 120 (7-amino-4-methylcoumarin), pyrrolyl coumarin 7-(1H-pyrrol-1-yl)-4-methyl-2H-1-benzopyran-2-one, and carbazole-coumarin hybrid 10H-4-methyl-2H-2-oxopyrano [5,6-b]carbazole, have been studied using B3LYP time-dependent density functional theory (TDDFT). The solvent effect has been taken into account using the polarizable continuum model. The spectra calculated using TDDFT agree well with the experimental absorption spectra. The electronic structures and the solvent effect for the low-lying singlet excited states have been investigated. The HOMO of the pyrrolyl coumarin is localized on the pyrrolyl ring, while the HOMO in the other 7-aminocoumarins is delocalized over the entire molecule. This leads to the weak fluorescence of the pyrrolyl coumarins found in experiments. The HOMO and next HOMO in carbazole-coumarin hybrids have similar orbital energy values, which is not the case in the other 7-aminocoumarin derivatives. This leads to the additional peaks found in the 30,000 -40,000 cm Ϫ1 region of the observed absorption spectra, which are specific for carbazole-coumarin hybrids.

Excited states of two 7-aminocoumarin derivatives, coumarin 120 (7-amino-4-methylcoumarin) and coumarin 151 (7-amino-4-trifluoromethylcoumarin), were investigated using generalized multiconfigurational quasidegenerate perturbation theory (GMC-QDPT), multiconfigurational quasidegenerate perturbation theory (MC-QDPT) and time-dependent density functional theory (TDDFT) with the B3LYP and CAM-B3LYP functionals. The absorption and fluorescence spectra of C120 and C151 were calculated. We elucidated the characters of the low-lying states of C120 and C151. The absorption spectra calculated with GMC-QDPT and TDDFT B3LYP agreed well with the experimental data, while for the fluorescence spectra, the TDDFT calculations overestimated the fluorescence spectra compared to GMC-QDPT calculations. Utilizing active spaces with large numbers of electrons and orbitals for reference functions, GMC-QDPT showed a better performance than MC-QDPT with a complete active space self-consistent field (CASSCF) reference of active space with smaller number of electrons and orbitals. In our gas phase calculation, we found that the optimized structures for the first excited states have a planar amino group with a CN single bond, while the amino group is pyramidal in the ground state.

The solvent effect on the steady-state and time-resolved fluorescence spectra of coumarin 120 in water was studied utilizing a molecular dynamics simulation with combined quantum mechanical/molecular mechanical method. The constructed steady-state fluorescence spectra reproduced the Stokes shift of the experimental data. The solvent effects on the spectra were examined by constructing three different spectra: spectra using the entire system, spectra including water molecules only in the first solvent shell, and spectra excluding all water molecules. We found that the variation in C-C bond length makes the largest contribution to the solvent shift in the fluorescence spectrum, which indicates the importance of the electronic structure variation.