Relief of excited-state antiaromaticity enables the smallest red emitter
Heechan Kim1, Woojin Park2, Younghun Kim1
1Department of Chemistry, Seoul National University, Seoul, Korea.
Abstract:
It is commonly accepted that a large π-conjugated system is necessary to realize low-energy electronic transitions. Contrary to this prevailing notion, we present a new class of light-emitters utilizing a simple benzene core. Among different isomeric forms of diacetylphenylenediamine (DAPA), o- and p-DAPA are fluorescent, whereas m-DAPA is not. Remarkably, p-DAPA is the lightest (FW = 192) molecule displaying red emission. A systematic modification of the DAPA system allows the construction of a library of emitters covering the entire visible color spectrum. Theoretical analysis shows that their large Stokes shifts originate from the relief of excited-state antiaromaticity, rather than the typically assumed intramolecular charge transfer or proton transfer. A delicate interplay of the excited-state antiaromaticity and hydrogen bonding defines the photophysics of this new class of single benzene fluorophores. The formulated molecular design rules suggest that an extended π-conjugation is no longer a prerequisite for a long-wavelength light emission.
Related Concept Videos
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
Photochemical Electrocyclic Reactions: Stereochemistry
Selection Rules: Photochemical Activation
Aryldiazonium Salts to Azo Dyes: Diazo Coupling
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3
Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between...
Variables Affecting Phosphorescence and Fluorescence


