title: Insight into the Amino-Type Excited-State Intramolecular Proton Transfer Cycle Using N-Tosyl Derivatives of 2-(2'-Aminophenyl)benzothiazole.
abstract: 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.
authors: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors: Chi-Lin
authors: CL
authors: Chen
authors: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors: Huan-Wei
authors: HW
authors: Tseng
authors: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors: Yi-An
authors: YA
authors: Chen
authors: Jun-Qi
authors: JQ
authors: Liu
authors: Department of Medical Education, Chung Shan Medical University , Taichung 40201, Taiwan.
authors: Chi-Min
authors: CM
authors: Chao
authors: Department of Medical Education, Chung Shan Medical University , Taichung 40201, Taiwan.
authors: Kuan-Miao
authors: KM
authors: Liu
authors: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors: Tzu-Chieh
authors: TC
authors: Lin
authors: Cheng-Hsien
authors: CH
authors: Hung
authors: Yen-Lin
authors: YL
authors: Chou
authors: Ta-Chun
authors: TC
authors: Lin
authors: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors: Pi-Tai
authors: PT
authors: Chou