Electronic Structures And Spectral Properties Of 3-Pyrrolidinobenzanthrone And D-Luciferin

In the present paper, the quantum chemical methods were employed to study the absorption and emission spectra of 3-Pyrrolidinobenzanthrone and D-Luciferin. The lectronic structures, the spectral properties, the effects of different exchange correlation functionals, basis sets and solvent on the absorption and emission spectra, and the mechanism of intermolecular excited-state proton transfer were analyzed in detail.1. Electronic structures and spectral properties of 3-pyrrolidinobenzanthroneIn this section, the geometries of the ground and the first excited states of 3-pyrrolidinobenzanthrone were optimized using the quantum chemistry methods, and the obtained structural parameters were compared with the experimental data. The time-dependent density functional theory (TD-DFT) calculations were performed to estimate the absorption and emission spectra of 3-pyrrolidinobenzanthrone both in gas-phase and solutions. In addition, the effects of different exchange correlation functionals, basis sets and solvent on the absorption and emission spectra were analyzed in detail. It was found that the strongest absorption and emission band of 3-pyrrolidinobenzanthrone both are assigned to a charge chansfer (CT) state ofππ* character. The result of the B3LYP functional reproduces the experimental absorption spectrum very well, and the functional MPWK predicts accurately the emission energy of the first excited state with intramolecular charge transfer (ICT) feature. The calculated results indicated that the solvent effects have no much influence on the absorption spectrum, but impact heavily on the emission one. The thoeretical results were in agreement with the experimental observations.2. Theoretical study on the electronic structures, spectral Properties, and the mechanism of intermolecular excited-state proton transfer of D-Luciferin In this section, The geometries of the ground and the first excited states of D-Luciferin (ROH) and the deprotonated form (RO-) were optimized using the quantum chemistry methods, according to the corresponding optimized structures, the absorption and emission spectra in different environments were calculated using the time-dependent density functional theory. The solvent effect was considered by the polarizable continuum model. The calculated results indicated that the ROH is not a dual fluorescence molecule, although its first excited state is a charge transfer (CT) state. In the Ethanol solvent, the two emission bands of the D-Luciferin are originated from two compounds, the short wavelengths emission band (450 nm) is from the excited ROH, and the long wavelengths emission band (530 nm) is from the excited RO-. In water, the fluorescence band at 530nm from RO-. In pure acetonitrile, the fluorescence band at 430nm from ROH. It is found that the ratio of peak intensities of RO-and ROH is depend on the reaction activation of intermolecular excited-state proton transfer (ESPT) energy of ROH. The absorption and decay pathways of the ROH in solvent are suggested based on the theoretical calculations. The calculated absorption and emission spectra are in good agreement with the experimental observations.