研究目的
To investigate the low-lying electronic states (S0, S1, and T1) of five phenol ortho-derivatives and explore the ortho-effect on their structures and properties from a photochemistry viewpoint.
研究成果
The CASSCF and B3LYP calculations reveal that S1 structures of 2-nitrophenol, salicylaldehyde, and 2-acetylphenol are H transfer structures, supporting barrierless ESIPT processes, while salicylamide and salicylic acid have S1 structures similar to ground states, explaining their strong fluorescence. All T1 structures are H transfer. Intramolecular hydrogen bonding is present in all states, with variations in strength. Excitation energies and oscillator strengths agree well with experiments. Transitions are π-π* and involve HOMO to LUMO orbitals. Ortho-effect influences excited-state conformations and isomerization pathways, dependent on substituent nature.
研究不足
The study is limited to computational methods, which may not fully capture experimental dynamics. The basis sets and active space choices could affect accuracy, and only specific ortho-derivatives are considered, potentially limiting generalizability. Experimental validation is partial, relying on comparisons with existing data.
1：Experimental Design and Method Selection:
The study uses computational methods, specifically the complete active space self-consistent field (CASSCF) and B3LYP density functional theory (DFT) methods, to optimize structures and calculate excitation energies. The CASSCF method employs an active space of 10 electrons in 8 orbitals (CASSCF(10,8)), and TD-DFT is used for vertical excitation energies.
2：Sample Selection and Data Sources:
Five ortho-derivatives of phenol are studied: 2-nitrophenol, salicylaldehyde, 2-acetylphenol, salicylamide, and salicylic acid. These are selected as model systems for intramolecular hydrogen bonding and ortho-effect studies.
3：List of Experimental Equipment and Materials:
Computational software GAUSSIAN03 is used for all calculations. Basis sets include 6-311+g(d,p) for DFT and cc-pVDZ for CASSCF.
4：Experimental Procedures and Operational Workflow:
Structures are optimized for S0, T1, and S1 states using CASSCF and B3LYP methods. Harmonic frequencies are computed to confirm minima. Vertical excitation energies are calculated using TD-DFT. Molecular orbitals are analyzed to determine transition characters.
5：Data Analysis Methods:
Results are compared with experimental data from references. Geometry parameters, excitation energies, oscillator strengths, and orbital transitions are analyzed to discuss ortho-effect and hydrogen bonding interactions.
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