Provided the advantage of spatiotemporal control with low-energy, visible light, organic donor-acceptor (D–A) type chromophores are employed in an array of techniques ranging from organic synthesis to cellular imaging. Still yet, the application of D–A type dyes is limited in many regards often due to low quantum yields, short excited state lifetimes, an inherent polarity sensitivity that inhibits photochemical processes. While methods have been developed to inhibit excited state quenching mechanisms such as external conversion and twisted intramolecular charge transfer (TICT), the task of engineering a practical and generalized method to control these dynamics in a bifunctional manner remains persistent. In this work we characterize and apply a novel method to improve excited state lifetimes and quantum yields through the inhibition of solvent-solute interactions with molecular excited states while simultaneously mitigating effect of TICT. Our designed dialkylamino donor utilizes a subtle amide based modification of the beta-position to create a structural buffer to exclude solvent interactions. Using fluorescence lifetime and quantum yield as readout methods, we show nearly 9-fold improvements in the photophysical properties of these 4-amino-7-nitrobenzoxadiazole beta-amide derivatives in ethanol relative to a dimethylamino control. Further we demonstrate that this modification works cooperatively with TICT inhibiting, small azacyclic donors, and that its application is broadly effective in D–A type chromophores, including coumarin, naphthalimide, and PRODAN based scaffolds. Using computational modeling and empirical characterization, we demonstrate that the beta-amide donor effectively inhibits solvent interaction with the excited state while simultaneously increasing the energy barrier of rotation about the donating group. We have applied these dyes to cellular imaging, showing quantitative increases in brightness, and future applications include application to chemical systems such as photolabile protecting groups.

Inhibiting excited state quenching mechanisms in donor-acceptor type chromophores with solvent-excluding substituents

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.