Single‐Benzene Dual‐Emitters Harness Excited‐State Antiaromaticity for White Light Generation and Fluorescence Imaging

Abstract

Molecular emitters simultaneously generating light at different wavelengths have wide applications. With a small molecule, however, it is challenging to realize two independent radiative pathways. We invented the first examples of dual-emissive singlebenzene fluorophores (SBFs). Two emissive tautomers are generated by synthetic modulation of the hydrogen bond acidity, which opens up pathways for excited-state proton transfer. White light is produced by a delicate balance between the energy and intensity of the emission from each tautomer. We show that the excitedstate antiaromaticity of the benzene core itself dictates the proton movements driving the tautomer equilibrium. Using this simple benzene platform, a fluorinated SBF was synthesized with a record high solubility in perfluorocarbon solvents. White light-emitting devices and multicolor imaging of perfluorocarbon nanodroplets in live cells demonstrate the practical utility of these molecules.

Small is Beautiful: Electronic Origin and Synthetic Evolution of Single-Benzene Fluorophores

“…This is the first example of a molecule leveraging ESAA to establish an excited-state equilibrium between two tautomers on a single-benzene platform. 2 The validity of the NICS analysis (CASSCF-GIAO calculations) is independently supported by the changes in the computed isotropic shielding To demonstrate the general applicability of our ESAA relief model, we conducted computational studies on known SBFs 7 and 9 (Figure 1). 28,30 As shown in Figure 11, both SBFs become antiaromatic upon vertical excitation.…”

“…Over the past decade, various research groups have explored small fluorophores built on a single benzene ring. ,,− Collectively named as single-benzene fluorophores (SBFs, Figure ), these molecules have intriguing photophysical properties. Equipped with aliphatic amine or alkyloxy groups as electron-donor groups (EDGs), and alkenyl, sulfonyl, or ester groups as electron-acceptor groups (EAGs) around the benzene core, they are capable of absorbing and emitting light in the visible region.…”

“…We recently introduced diacetylphenylenediamines (DAPAs) as the newest additions to the growing list of SBFs (Figure ). , During the investigation, we discovered that the prevailing charge transfer paradigm does not adequately explain their photophysical properties, as these molecules exhibit little solvatochromic behavior. Moreover, it seemed counterintuitive to suggest distinct charge separation occurring across the small benzene core.…”

“…Inset: Digital images of (a, b) DAPA isomers, and (c) N -functionalized derivatives of p -DAPA ( 23 – 28 , left to right; see Scheme for chemical structures) in CHCl 3 under irradiation of 365 nm UV light. Reproduced with permission from refs , . Copyright (2021) Nature Publishing Group and (2023) Wiley-VCH.…”

“…(c) Fluorescence image of 26 in CHCl 3 under irradiation with 365 nm UV light. Data taken from ref .…”