Non-condon Effect on Ultrafast Excited-State Intramolecular Proton Transfer

Yoneda, Yusuke; Sotome, Hikaru; Mathew, Reshma; Lakshmanna, Yapamanu Adithya; Miyasaka, Hiroshi

doi:10.1021/acs.jpca.9b09085

Cited by 26 publications

(26 citation statements)

References 47 publications

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“…However, it has to be noted that the N−H or O−H stretching may not be directly involved in the ESIPT reactions, but those vibrational modes that are associated with the changes of the H-bond in distance and/ or angle. 39,86 Therefore, our calculation may not directly reflect the experimental observation, due mainly to the multiple dimensional reaction coordinates that cannot be fully considered at this stage. Overall, these results indicate that the ESIPT kinetics and thermodynamics are strongly correlated in the PBTs derivatives.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Correlation between Kinetics and Thermodynamics for Excited-State Intramolecular Proton Transfer Reactions

2021

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Finding the relation between thermodynamics and kinetics for a reaction is of fundamental importance. Here, the thermodynamics and kinetics correlation of excited-state intramolecular proton transfer (ESIPT) was investigated by the TD-DFT calculation under the CAM-B3LYP/6-311+G** level. We choose the family 2-(2′-aminophyenyl)benzothiazole and its amino derivatives as paradigms, which all possess the NH-type intramolecular hydrogen bond (H-bond), and investigate the corresponding ESIPT reaction. The H-bond strength can be systematically tuned, so both activation energy ΔG ‡ and free energy difference between proton transfer tautomer (T*, product) and normal species (N*, reactant) ΔG T*–N* can be varied. To minimize the environmental interference such as solvent external H-bond and polarity perturbation, a nonpolar solvent such as cyclohexane is chosen as a bath with a polarizable continuum solvation model for the calculation. As a result, the comprehensive computational approach reveals a linear relationship between ΔG T*–N* and ΔG ‡, which can be expressed as ΔG ‡ = ΔG 0 + αΔG T*–N*. The fundamental insight is reminiscent of the Bell–Evans–Polanyi (BEP) principle where α represents the character of the position of the transition state along the proton motion coordinate. In other words, the more exergonic the ESIPT reaction is, the faster the proton transfer rate can be observed. To verify that such a correlation is not a sporadic event, another ESIPT family with an −OH proton, 1-hydroxy-11H-benzo[b]fluoren-11-one and its derivatives, was also investigated and proved to follow the BEP principle as well. Unlike the quantum mechanics description of proton transfer where either proton tunneling is dominant or solute/solvent is coupled in ESIPT, this work demonstrates that reaction kinetics and thermodynamics are strongly correlated within the same class of ESIPT molecules with an intrinsic barrier free from solvent perturbation, being faster with the more exergonic reaction.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Correlation between Kinetics and Thermodynamics for Excited-State Intramolecular Proton Transfer Reactions

2021

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“…Among a variety of H-bond associated research directions, one field should be credited to the proton transfer reaction in the electronically excited state. − Upon photoexcitation, driven by the changes of the acidity and basicity in the excited state, the transfer of a proton from the OH or NH proton-donating site to the O or N proton-accepting site becomes feasible. When it takes place within the molecular unit, the process is dubbed as the excited-state intramolecular proton transfer (ESIPT), which has been receiving considerable attention in both fundamental − and applied researches. − On the one hand, the result of ESIPT forms a proton-transfer isomer, namely, the tautomer, in the excited state, which does not exist in the ground state thermally and accordingly gives rise to an anomalously large Stokes shift emission (cf. the non-proton transfer, normal emission).…”

Section: Introductionmentioning

confidence: 99%

Chapter Open for the Excited-State Intramolecular Thiol Proton Transfer in the Room-Temperature Solution

et al. 2021

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We report here, for the first time, the experimental observation on the excited-state intramolecular proton transfer (ESIPT) reaction of the thiol proton in room-temperature solution. This phenomenon is demonstrated by a derivative of 3-thiolflavone (3TF), namely, 2-(4-(diethylamino)phenyl)-3mercapto-4H-chromen-4-one (3NTF), which possesses an SH•••O intramolecular H-bond (denoted by the dashed line) and has an S 1 absorption at 383 nm. Upon photoexcitation, 3NTF exhibits a distinctly red emission maximized at 710 nm in cyclohexane with an anomalously large Stokes shift of 12 230 cm −1 . Upon methylation on the thiol group, 3MeNTF, lacking the thiol proton, exhibits a normal Stokes-shifted emission at 472 nm. These, in combination with the computational approaches, lead to the conclusion of thiol-type ESIPT unambiguously. Further time-resolved study renders an unresolvable (<180 fs) ESIPT rate for 3NTF, followed by a tautomer emission lifetime of 120 ps. In sharp contrast to 3NTF, both 3TF and 3-mercapto-2-(4-(trifluoromethyl)phenyl)-4Hchromen-4-one (3FTF) are non-emissive. Detailed computational approaches indicate that all studied thiols undergo thermally favorable ESIPT. However, once forming the proton-transferred tautomer, the lone-pair electrons on the sulfur atom brings nonnegligible nπ* contribution to the S 1 ′ state (prime indicates the proton-transferred tautomer), for which the relaxation is dominated by the non-radiative deactivation. For 3NTF, the extension of π-electron delocalization by the diethylamino electron-donating group endows the S 1 ′ state primarily in the ππ* configuration, exhibiting the prominent tautomer emission. The results open a new chapter in the field of ESIPT, covering the non-canonical sulfur intramolecular H-bond and its associated ESIPT at ambient temperature.

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“…Another study revealed that optical excitation can directly prepare the electron–proton transfer photoproduct . However, it is important to note that all of these previous time-resolved spectroscopic studies have regarded the photoinduced PCET reaction as a state-to-state transition. ,− However, contrary to this treatment, electronically excited states are typically best described via mixing of different electronic configurations, and the degree of mixing can change throughout the course of the movement of electrons and protons. , Moreover, photoexcitation leads a system into a nonequilibrium distribution of many vibronic energy levels . For the above reasons, the mechanism of ultrafast photoinduced PCET remains essentially unexplored.…”

Section: Introductionmentioning

confidence: 99%

“…16,19−21 However, contrary to this treatment, electronically excited states are typically best described via mixing of different electronic configurations, and the degree of mixing can change throughout the course of the movement of electrons and protons. 22,23 Moreover, photoexcitation leads a system into a nonequilibrium distribution of many vibronic energy levels. 24 For the above reasons, the mechanism of ultrafast photoinduced PCET remains essentially unexplored.…”

Section: ■ Introductionmentioning

confidence: 99%

Electron–Nuclear Dynamics Accompanying Proton-Coupled Electron Transfer

et al. 2021

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Although photoinduced proton-coupled electron transfer (PCET) plays an essential role in photosynthesis, a full understanding of the mechanism is still lacking due to the complex nonequilibrium dynamics arising from the strongly coupled electronic and nuclear degrees of freedom. Here we report the photoinduced PCET dynamics of a biomimetic model system investigated by means of transient IR and two-dimensional electronic−vibrational (2DEV) spectroscopies, IR spectroelectrochemistry (IRSEC), and calculations utilizing long-range-corrected hybrid density functionals. This collective experimental and theoretical effort provides a nuanced picture of the complicated dynamics and synergistic motions involved in photoinduced PCET. In particular, the evolution of the 2DEV line shape, which is highly sensitive to the mixing of vibronic states, is interpreted by accurate computational modeling of the charge separated state and is shown to represent a gradual change in electron density distribution associated with a dihedral twist that occurs on a 120 fs time scale.

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Non-condon Effect on Ultrafast Excited-State Intramolecular Proton Transfer

Cited by 26 publications

References 47 publications

Correlation between Kinetics and Thermodynamics for Excited-State Intramolecular Proton Transfer Reactions

Correlation between Kinetics and Thermodynamics for Excited-State Intramolecular Proton Transfer Reactions

Chapter Open for the Excited-State Intramolecular Thiol Proton Transfer in the Room-Temperature Solution

Electron–Nuclear Dynamics Accompanying Proton-Coupled Electron Transfer

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