研究目的
To introduce a new facile pressure-induced approach to light up the invisible twisted intramolecular charge transfer (TICT) state in non-fluorescent molecules, specifically using coumarin 7 in acetonitrile solvent under high pressure, and to understand the mechanism through ultrafast spectroscopy and quantum chemical calculations.
研究成果
High pressure, specifically through liquid-solid phase transition in acetonitrile solvent, successfully lights up the invisible TICT state in coumarin 7 by restricting molecular rotation, leading to dual fluorescence. This approach provides a novel strategy for regulating TICT processes and has potential applications in optoelectronics and biomedicine. Future work could explore other molecules and solvents to generalize the findings.
研究不足
The study is limited to coumarin 7 in acetonitrile solvent; applicability to other molecules or solvents may vary. High-pressure experiments require specialized equipment like DACs, which may not be widely accessible. The quantum chemical calculations rely on specific functionals and models, which might not capture all nuances of molecular interactions. The phase transition and its effects are specific to the pressure range and solvent used.
1：Experimental Design and Method Selection:
The study uses high-pressure technology to induce liquid-solid phase transition in acetonitrile solvent, combined with steady-state fluorescence spectroscopy, ultrafast transient absorption spectroscopy, and quantum chemical calculations (DFT/TDDFT) to investigate the TICT state in coumarin 7 molecules.
2：Sample Selection and Data Sources:
Coumarin 7 (C7) dye was purchased from Sigma-Aldrich and dissolved in acetonitrile (ACN) solvent at a concentration of 1 × 10^-3 M. ACN was chosen for its low-pressure liquid-solid phase transition.
3：List of Experimental Equipment and Materials:
Equipment includes a tungsten lamp for absorption spectroscopy, a 400 nm semiconductor laser for fluorescence excitation, a high-resolution fiber optic spectrometer (HR4000, Ocean Optical), a femtosecond laser system (Coherent Libra), a diamond anvil cell (DAC) for high-pressure generation, and ruby chips for pressure calibration. Materials include C7 dye and ACN solvent.
4：Experimental Procedures and Operational Workflow:
Pressure was applied using a DAC calibrated with ruby fluorescence. Steady-state fluorescence spectra were measured at various pressures from 1 atm to
5：6 GPa. Ultrafast transient absorption spectroscopy was performed with a pump-probe setup using 400 nm excitation. Quantum chemical calculations were conducted using Gaussian software with B3LYP functional and TZVP basis set, including solvent effects via PCM. Data Analysis Methods:
Global fitting with multi-exponential decay models was used for transient absorption data analysis. Fluorescence spectra were normalized and analyzed for peak shifts and intensities. Computational results were compared with experimental data to interpret molecular behaviors.
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