Toward Quantitative Prediction of Fluorescence Quantum Efficiency by Combining Direct Vibrational Conversion and Surface Crossing: BODIPYs as an Example

Qi Ou; Qian Peng; Zhigang Shuai

doi:10.1021/acs.jpclett.0c02054

Toward Quantitative Prediction of Fluorescence Quantum Efficiency by Combining Direct Vibrational Conversion and Surface Crossing: BODIPYs as an Example

J Phys Chem Lett. 2020 Sep 17;11(18):7790-7797. doi: 10.1021/acs.jpclett.0c02054. Epub 2020 Sep 3.

Authors

Qi Ou¹, Qian Peng², Zhigang Shuai¹

Affiliations

¹ MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, China.
² CAS Key Laboratory of Organic Solids, Institute of Chemistry of the Chinese Academy of Sciences, Zhonguancun Beiyijie 2, Beijing 100190, China.

PMID: 32787317
DOI: 10.1021/acs.jpclett.0c02054

Abstract

Accurate theoretical description of the electronic structure of boron dipyrromethene (BODIPY) molecules has been a challenge, let alone the prediction of fluorescence quantum efficiency. In this Letter, we show that the electronic structures of BODIPYs can be accurately evaluated via the spin-flip time-dependent density functional theory with the B3LYP functional. With the resulting electronic structures, the experimental spectral line shapes of representative BODIPYs are successfully reproduced by our previously developed thermal vibration correlation function method. Most importantly, a two-channel scheme is proposed to describe the internal conversion of S₁ to S₀ in BODIPYs: channel I via direct vibrational relaxation within the harmonic region and channel II via a distorted S₀/S₁ minimum energy crossing point well away from the harmonic region. The fluorescence quantum yields are accurately predicted within this two-channel scheme, which can therefore serve as a generalized method for predicting the photophysical parameters of organic fluorescent compounds.