Insight into the Amino-Type Excited-State Intramolecular Proton Transfer Cycle Using N-Tosyl Derivatives of 2-(2‿Aminophenyl)benzothiazole

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• 作者：Chi-Lin Chen ; Huan-Wei Tseng ; Yi-An Chen ; Jun-Qi Liu ; Chi-Min Chao ; Kuan-Miao Liu ; Tzu-Chieh Lin ; Cheng-Hsien Hung ; Yen-Lin Chou ; Ta-Chun Lin ; Pi-Tai Chou
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：February 25, 2016
• 年：2016
• 卷：120
• 期：7
• 页码：1020-1028
• 全文大小：559K
• ISSN：1520-5215

文摘

Studies have been carried out to gain insight in to an overall excited-state proton transfer cycle for a series of N-tosyl derivatives of 2-(2′-aminophenyl)benzothiazole. The results indicate that followed by ultrafast (<150 fs) excited-state intramolecular proton transfer (ESIPT), the titled compounds undergo rotational isomerization along the C₁–C₁′ bond. For the model compound 2-(2′-tosylaminophenyl)benzothiazole (PBT-NHTs) the subsequent cis-trans isomerization process in both triplet and ground states are probed by nanosecond transient absorption (TA) and two-step laser-induced fluorescence (TSLIF) spectroscopy. Both TA and TSLIF results indicate the existence of a long-lived trans-tautomer species in the ground state with a lifetime of few microseconds. The experimental results correlate well with the theoretical approach, which suggests that PBT-NHTs proton transfer tautomer generated in the excited state undergoes intramolecular C₁–C₁′ rotation to ∼100° between benzothiazole and phenyl moieties in which the energetics for the S₁ and T₁ states are nearly identical. As a result, the intersystem crossing between S₁ and T₁ states serves as a fast deactivation pathway for the excited-state cis-tautomer to channel into both cis- and trans-tautomer in their respective T₁ states, followed by the dominant T₁-S₀ radiationless deactivation to populate the trans-tautomer in the ground state. The trans-tautomer species in the S₀ state proceeds with intermolecular double proton transfer to regenerate the cis-normal form. An overall proton-transfer cycle describing the amino-type ESIPT and the subsequent isomerization processes is thus depicted in detail.