Time-Domain Study of the S3 State of 9-Fluorenone

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• 作者：Thiemo Gerbich ; J枚rg Herterich ; Juliane K枚hler ; Ingo Fischer
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：February 27, 2014
• 年：2014
• 卷：118
• 期：8
• 页码：1397-1402
• 全文大小：333K
• 年卷期：v.118,no.8(February 27, 2014)
• ISSN：1520-5215

文摘

We report a combined gas phase and solution phase study of 9-fluorenone. The structure and dynamics of isolated fluorenone in the S₃-state were studied by resonant enhanced multiphoton ionization with picosecond pulses in a free jet of molecules excited between 285 and 312 nm. Ionization was performed with a second ps-pulse at 351 nm. The electronic spectrum is structured, and the origin of the C ¹B₂ 鈫?X ¹A₁ transition was observed at 32鈥?22 cm^鈥?. Several vibrational fundamentals appear in the spectrum. In the gas phase we observe a biexponential decay, which suggests an internal conversion to the coupled S₁/S₂-state within 10鈥?0 ps. A further decay that is assigned to intersystem crossing was found to be longer than 500 ps. In addition to the gas phase measurements, we studied the photophysics of 9-fluorenone in cyclohexane by femtosecond-time-resolved transient absorption spectroscopy and observed very similar dynamics upon excitation to the S₃ state: It deactivates within 8鈥?1 ps by internal conversion, followed by intersystem crossing within 120鈥?50 ps, forming a long-lived triplet state. Experiments in acetonitrile, however, showed marked differences. Intersystem crossing is ineffective in polar solvents because the lowest excited singlest state is of 蟺蟺* character and does not interact with the ³蟺蟺*.