Excited-State Decay Paths in Tetraphenylethene Derivatives.
The photophysical properties of tetraphenylethene (TPE) compounds may differ widely depending on the substitution pattern, for example, with regard to the fluorescence quantum yield ϕfand the propensity to exhibit aggregation-induced emission (AIE). We report combined electronic structure calculations and nonadiabatic dynamics simulations to study the excited-state decay mechanisms of two TPE derivatives with four methyl substituents, either in the meta position (TPE-4mM, ϕf= 0.1%) or in the ortho position (TPE-4oM, ϕf= 64.3%). In both cases, two excited-state decay pathways may be relevant, namely, photoisomerization around the central ethylenic double bond and photocyclization involving two adjacent phenyl rings. In TPE-4mM, the barrierless S1cyclization is favored; it is responsible for the ultralow fluorescence quantum yield observed experimentally. In TPE-4oM, both the S1photocyclization and photoisomerization paths are blocked by non-negligible barriers, and fluorescence is thus feasible. Nonadiabatic dynamics simulations with more than 1000 surface hopping trajectories show ultrafast cyclization upon photoexcitation of TPE-4mM, whereas TPE-4oM remains unreactive during the 1 ps simulations. We discuss the chances for spectroscopic detection of the postulated cyclic photoproduct of TPE-4mM and the relevance of our findings for the AIE process.
Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University Beijing 100875, China.
Yuan-Jun
YJ
Gao
Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University Beijing 100875, China.
Xue-Ping
XP
Chang
Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University Beijing 100875, China.
Xiang-Yang
XY
Liu
School of Chemistry and Chemical Engineering, Beijing Institute of Technology , Beijing 100081, China.
Quan-Song
QS
Li
Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University Beijing 100875, China.
Ganglong
http://orcid.org/0000-0002-9752-1659
G
Cui
Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.
Walter
http://orcid.org/0000-0001-6780-0350
W
Thiel