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1. Excited State Intramolecular Proton Transfer with Nuclear-Electronic Orbital Ehrenfest Dynamics

   https://doi.org/10.1021/acs.jpclett.1c00564  

   Zhao, Luning ; Wildman, Andrew ; Pavošević, Fabijan ; Tully, John C. ; Hammes-Schiffer, Sharon ; Li, Xiaosong ( April 2021 , The Journal of Physical Chemistry Letters)

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2. Metal‐Free Organic Triplet Emitters with On–Off Switchable Excited State Intramolecular Proton Transfer

   https://doi.org/10.1002/adfm.202201256  

   Shao, Wenhao ; Hao, Jie ; Jiang, Hanjie ; Zimmerman, Paul M. ; Kim, Jinsang ( April 2022 , Advanced Functional Materials)

   Metal‐free organic triplet emitters are an emerging class of organic semiconducting material. Among them, molecules with tunable emission responsive to environmental stimuli have shown great potential in solid‐state lighting, sensors, and anti‐counterfeiting systems. Here, a novel excited‐state intramolecular proton transfer (ESIPT) system is proposed showing the activation of thermally activated delayed fluorescence (TADF) or room‐temperature phosphorescence (RTP) simultaneously from both keto and enol tautomers. The prototype ESIPT triplet emitters exhibit up to 50% delayed emission quantum yield. Their enol–keto tautomerization can be switched by controlling the matrix acidity in doped polymer films. Taking advantage of these unique properties, “on‐off” switchable triplet emission systems controlled by acid vapor annealing, as well as photopatterning systems capable of generating facile and high‐contrast emissive patterns, are devised.

    

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3. Photogrammetry of Ultrafast Excited-State Intramolecular Proton Transfer Pathways in the Fungal Pigment Draconin Red

   https://doi.org/10.3390/molecules28083506  

   Solaris, Janak ; Krueger, Taylor D. ; Chen, Cheng ; Fang, Chong ( April 2023 , Molecules)

   Proton transfer processes of organic molecules are key to charge transport and photoprotection in biological systems. Among them, excited-state intramolecular proton transfer (ESIPT) reactions are characterized by quick and efficient charge transfer within a molecule, resulting in ultrafast proton motions. The ESIPT-facilitated interconversion between two tautomers (PS and PA) comprising the tree fungal pigment Draconin Red in solution was investigated using a combination of targeted femtosecond transient absorption (fs-TA) and excited-state femtosecond stimulated Raman spectroscopy (ES-FSRS) measurements. Transient intensity (population and polarizability) and frequency (structural and cooling) dynamics of –COH rocking and –C=C, –C=O stretching modes following directed stimulation of each tautomer elucidate the excitation-dependent relaxation pathways, particularly the bidirectional ESIPT progression out of the Franck–Condon region to the lower-lying excited state, of the intrinsically heterogeneous chromophore in dichloromethane solvent. A characteristic overall excited-state PS-to-PA transition on the picosecond timescale leads to a unique “W”-shaped excited-state Raman intensity pattern due to dynamic resonance enhancement with the Raman pump–probe pulse pair. The ability to utilize quantum mechanics calculations in conjunction with steady-state electronic absorption and emission spectra to induce disparate excited-state populations in an inhomogeneous mixture of similar tautomers has broad implications for the modeling of potential energy surfaces and delineation of reaction mechanisms in naturally occurring chromophores. Such fundamental insights afforded by in-depth analysis of ultrafast spectroscopic datasets are also beneficial for future development of sustainable materials and optoelectronics. 

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4. Illuminating Excited-State Intramolecular Proton Transfer of a Fungi-Derived Red Pigment for Sustainable Functional Materials

   https://doi.org/10.1021/acs.jpcc.1c09773  

   Krueger, Taylor D. ; Solaris, Janak ; Tang, Longteng ; Zhu, Liangdong ; Webber, Carter ; Van Court, Ray C. ; Robinson, Seri C. ; Ostroverkhova, Oksana ; Fang, Chong ( January 2022 , The Journal of Physical Chemistry C)
5. Excitation Energy-Dependent, Excited-State Intramolecular Proton Transfer-Based Dual Emission in Poor Hydrogen-Bonding Solvents

   https://doi.org/10.1021/acs.jpca.2c03668  

   Hurley, Joseph J. ; Zhu, Lei ( September 2022 , The Journal of Physical Chemistry A)