Excited-State Dynamics of (Organophosphine)gold(I) Pyrenyl Isomers
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Abstract
Ultrafast dynamics of isomeric (tricyclohexylphosphine)gold(I) pyrenyl complexes have been measured in chloroform and cyclohexane at room temperature. Internal conversion from an upper excited singlet (S<sub><i>n</i></sub>) to the S<sub>1</sub> state occurs in less than 200 fs after 340 nm excitation. Internal conversion in the singlet manifold is followed by 11−100 ps intersystem crossing to a receiver triplet state depending on the site of pyrene metalation. The receiver triplet state (T<sub><i>n</i></sub>) then decays to the T<sub>1</sub> state on an ultrafast time scale, which decays back to the S<sub>0</sub> state on a microseconds time scale in N<sub>2</sub>-saturated conditions. Time-dependent density functional theory calculations on model complexes predict an accidental degeneracy of the S<sub>1</sub> and T<sub>2</sub> states of the 1-pyrenyl. No such degeneracy occurs for the 2-pyrenyl isomer. A small S<sub>1</sub>−T<sub>2</sub> energy gap promotes the 10-fold increase in the intersystem crossing rate in the 1-pyrenyl complex