Excited-State Decay Paths in Tetraphenylethene Derivatives

Area of Science:

• Photochemistry
• Computational Chemistry
• Materials Science

Background:

• Tetraphenylethene (TPE) derivatives exhibit diverse photophysical properties, including fluorescence quantum yield and aggregation-induced emission (AIE), which are sensitive to structural modifications.
• Understanding excited-state decay mechanisms is crucial for designing TPE-based materials with desired optical properties.

Purpose of the Study:

• To investigate the excited-state decay mechanisms of two tetraphenylethene (TPE) derivatives with different methyl substituent positions.
• To elucidate the relationship between molecular structure, substitution pattern, and photophysical properties like fluorescence quantum yield and aggregation-induced emission (AIE).

Main Methods:

• Combined electronic structure calculations and nonadiabatic dynamics simulations were employed.
• Over 1000 surface hopping trajectories were simulated to model excited-state decay pathways.
• Computational analysis focused on photoisomerization and photocyclization pathways.

Main Results:

• TPE-4mM, with meta-positioned methyl groups, exhibits a barrierless S1 cyclization pathway, leading to an ultralow fluorescence quantum yield (0.1%).
• TPE-4oM, with ortho-positioned methyl groups, has blocked S1 photocyclization and photoisomerization pathways due to significant energy barriers, enabling high fluorescence (64.3%).
• Nonadiabatic dynamics simulations confirmed ultrafast cyclization in TPE-4mM and stability in TPE-4oM within 1 ps.

Conclusions:

• The substitution pattern of methyl groups in TPE derivatives critically determines their excited-state decay routes.
• Barrierless photocyclization in TPE-4mM explains its low fluorescence, while blocked pathways in TPE-4oM facilitate high fluorescence.
• Findings provide insights into controlling AIE properties and suggest potential spectroscopic detection of photoproducts.