Ultrafast Excited-State Dynamics of ortho-Terphenyl and 1,2-Diphenylcyclohexene: The Role of 鈥淓thylenic Twisting鈥?in the Nonadiabatic Photocyclization of Stilbene Analogs

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• 作者：Molly C. Smith ; Joshua A. Snyder ; Benjamin C. Streifel ; Arthur E. Bragg
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2013
• 出版时间：June 6, 2013
• 年：2013
• 卷：4
• 期：11
• 页码：1895-1900
• 全文大小：310K
• 年卷期：v.4,no.11(June 6, 2013)
• ISSN：1948-7185

文摘

Nonadiabatic photocyclization is the fundamental step underlying photoswitching and light-assisted bond formation within diarylethylenes, yet the details of the nuclear dynamics leading to cyclization remain unclear. We have examined the ultrafast excited-state dynamics of o-terphenyl (OTP) and 1,2-diphenylcyclohexene (DPCH) in solution to determine how variation in structural constraints impacts the course of nonadiabatic photocyclization specifically in stilbenoids. Measured spectral dynamics reflect cyclization through a S₁-to-S₀ transition for both systems on picosecond time scales, with excited-state decay appreciably faster for DPCH versus OTP. Supportive ab initio calculations reveal a higher energetic penalty in OTP versus DPCH for reaching the lowest-energy conical intersection from the S₁ minimum; this penalty is associated primarily with twisting about the carbon鈥揷arbon bond that bridges terminal phenyl groups, a structural change that has a critical role in nonadiabatic cis鈥搕rans isomerization of diarylethylenes. Findings provide a new experimental perspective on the elusive nuclear dynamics underlying cis-stilbene photocyclization.

Keywords:

photocyclization; nonadiabatic dynamics; stilbene; conical intersection; molecular photoswitching