Electronic and Steric Tuning of Excited State Proton Transfer in Water

30 September 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The photoinduced proton transfer powers a myriad of chemical and biological processes. Rational design for such functionality requires the fundamental understanding of structure-photoacidity and thermodynamics-kinetics relationships. Herein, we systematically tune chemical structure at electron donor and acceptor moieties of an archetypal photoacid, the green fluorescent protein (GFP) chromophore. We quantitatively demonstrate that thermodynamic driving force of excited-state proton transfer (ESPT) in water is governed by intramolecular (electronic, steric) and intermolecular (electronic) effects exerted by the substituent. To rationalize the observed kinetics, we propose different treatments for fluorescent and nonfluorescent photoacids with driving force dependent on relative rates of ESPT and Franck-Condon relaxation. In particular, the addition of Franck-Condon excess energy to free energy difference better predicts ESPT rate/occurrence in a revised Förster equation for nonfluorescent photoacids. Furthermore, the thermodynamics-kinetics relationship for ESPT in these GFP-chromophore derivatives follows Bell-Evans-Polanyi principle, offering the desirable predictive power for engineerable photoacids with targeted properties.

Keywords

structure-photoacidity relationships
thermodynamics-kinetics relationships
intramolecular and intermolecular effects
Franck-Condon excess energy
revised Förster equation
multivariable linear regression
fluorescent and nonfluorescent photoacids
femtosecond stimulated Raman

Supplementary materials

Title
Description
Actions
Title
Supplementary Information
Description
Supplementary Information (a combined PDF with methods, additional discussion sections, 24 figures, 9 tables, 34 NMR spectra, and 69 references).
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.