Using non-empirically tuned range-separated functionals with simulated emission bands to model fluorescence lifetimes

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Accurate calculation of fluorescence lifetimes is crucial for understanding photophysical processes.
• Time-dependent density functional theory (TD-DFT) is a widely used method for electronic structure calculations.

Purpose of the Study:

• To evaluate various exchange-correlation functionals within TD-DFT for their accuracy in predicting fluorescence lifetimes.
• To investigate the impact of molecular geometry optimization and vibronic effects on calculated lifetimes.

Main Methods:

• Time-dependent density functional theory (TD-DFT) calculations were performed.
• A range of exchange-correlation functionals (B3LYP, BMK, CAM-B3LYP, LC-BLYP, M06, M06-2X, M11, PBE0, ωB97, ωB97X) were tested.
• Non-empirical tuning of range-separation parameters for LC-BLYP* and ωB97X* functionals was employed.
• The influence of optimized ground and excited state geometries, as well as vibronic features, was assessed.

Main Results:

• Optimized molecular geometries significantly impact calculated fluorescence lifetimes.
• Inclusion of vibronic features further improves accuracy compared to vertical electronic transitions.
• The LC-BLYP* functional, with tuned range-separation parameters, yielded the most accurate fluorescence lifetimes.
• Unsigned errors for LC-BLYP* were predominantly within 1.5 ns of experimental data.

Conclusions:

• TD-DFT calculations can accurately predict fluorescence lifetimes when appropriate functionals and methods are used.
• The LC-BLYP* functional represents a significant improvement for fluorescence lifetime calculations.
• Considering geometric relaxation and vibronic coupling is essential for high-fidelity predictions.