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Wang JK, Wang CH, Wu CC, Chang KH, Wang CH, Liu YH, Chen CT, Chou PT. Hydrogen-Bonded Thiol Undergoes Unconventional Excited-State Intramolecular Proton-Transfer Reactions. J Am Chem Soc 2024; 146:3125-3135. [PMID: 38288596 PMCID: PMC10859960 DOI: 10.1021/jacs.3c10405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 01/06/2024] [Accepted: 01/08/2024] [Indexed: 02/08/2024]
Abstract
The chapter on the thiol-related hydrogen bond (H-bond) and its excited-state intramolecular proton-transfer (ESIPT) reaction was recently opened where compound 4'-diethylamino-3-mercaptoflavone (3NTF) undergoes ESIPT in both cyclohexane solution and solid, giving a 710 nm tautomer emission with an anomalously large Stokes shift of 12,230 cm-1. Considering the thiol H-bond to be unconventional compared to the conventional Pauling-type -OH or -NH H-bond, it is thus essential and timely to probe its fundamental difference between their ESIPT. However, thiol-associated ESIPT tends to be nonemissive due to the dominant nπ* character of the tautomeric lowest excited state. Herein, based on the 3-mercaptoflavone scaffold and π-elongation concept, a new series of 4'-substituted-7-diethylamino-3-mercaptoflavones, NTFs, was designed and synthesized with varied H-bond strength and 690-720 nm tautomeric emission upon ultraviolet (UV) excitation in cyclohexane. The order of their H-bonding strength was experimentally determined to be N-NTF < O-NTF < H-NTF < F-NTF, while the rate of -SH ESIPT measured by fluorescence upconversion was F-NTF (398 fs)-1 < H-NTF (232 fs)-1 < O-NTF (123 fs)-1 < N-NTF (101 fs)-1 in toluene. Unexpectedly, the strongest H-bonded F-NTF gives the slowest ESIPT, which does not conform to the traditional ESIPT model. The results are rationalized by the trend of carbonyl oxygen basicity rather than -SH acidity. Namely, the thiol acidity relevant to the H-bond strength plays a minor role in the driving force of ESIPT. Instead, the proton-accepting strength governs ESIPT. That is to say, the noncanonical thiol H-bonding system undergoes an unconventional type of ESIPT.
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Affiliation(s)
- Jian-Kai Wang
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of
China
| | - Chih-Hsing Wang
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of
China
| | - Chi-Chi Wu
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of
China
| | - Kai-Hsin Chang
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of
China
| | - Chun-Hsiang Wang
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of
China
| | - Yi-Hung Liu
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of
China
| | - Chao-Tsen Chen
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of
China
- Center
for Emerging Material and Advanced Devices, National Taiwan University, Taipei 10617, Taiwan, Republic of China
| | - Pi-Tai Chou
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of
China
- Center
for Emerging Material and Advanced Devices, National Taiwan University, Taipei 10617, Taiwan, Republic of China
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Lee J, Shin P, Chou PT, Joo T. Excited State Intramolecular Proton Transfer Dynamics of Derivatives of the Green Fluorescent Protein Chromophore. Int J Mol Sci 2023; 24:ijms24043448. [PMID: 36834871 PMCID: PMC9962057 DOI: 10.3390/ijms24043448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Revised: 02/04/2023] [Accepted: 02/04/2023] [Indexed: 02/11/2023] Open
Abstract
Excited state intramolecular proton transfer (ESIPT) dynamics of the o-hydroxy analogs of the green fluorescent protein (GFP) chromophore have been investigated by time-resolved spectroscopies and theoretical calculations. These molecules comprise an excellent system to investigate the effect of electronic properties on the energetics and dynamics of ESIPT and to realize applications in photonics. Time-resolved fluorescence with high enough resolution was employed to record the dynamics and the nuclear wave packets in the excited product state exclusively in conjunction with quantum chemical methods. The ESIPT are ultrafast occurring in 30 fs for the compounds employed in this work. Although the ESIPT rates are not affected by the electronic properties of the substituents suggesting barrierless reaction, the energetics, their structures, subsequent dynamics following ESIPT, and possibly the product species are distinct. The results attest that fine tuning of the electronic properties of the compounds may modify the molecular dynamics of ESIPT and subsequent structural relaxation to achieve brighter emitters with broad tuning capabilities.
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Affiliation(s)
- Junghwa Lee
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
| | - Pyoungsik Shin
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
| | - Pi-Tai Chou
- Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan, China
- Correspondence: (P.-T.C.); (T.J.)
| | - Taiha Joo
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
- Correspondence: (P.-T.C.); (T.J.)
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