2,6‐Bis(arylsulfonyl)anilines as Fluorescent Scaffolds through Intramolecular Hydrogen Bonds: Solid‐State Fluorescence Materials and Turn‐On‐Type Probes Based on Aggregation‐Induced Emission

Abstract

A series of 2,6‐bis[aryl(alkyl)sulfonyl]anilines were synthesized by nucleophilic aromatic substitution of 2,6‐dichloronitrobenzene with various aryl or alkyl thiolates (benzyl‐, phenyl‐, 2‐naphthyl‐, and 2‐aminophenyl thiolate), followed by hydrogenation and subsequent oxidation. All prepared 2,6‐bis[aryl‐(alkyl)sulfonyl]anilines showed high fluorescence emissions in the solid state; X‐ray structures revealed well‐defined intramolecular hydrogen bonds, which served to immobilize the rotatable amino group and generate a fluorescence enhancement in addition to improved photostability. Moreover, absorption and fluorescence spectra showed redshifts in the order of benzyl<phenyl<2‐naphthyl in solution and the solid state, and DFT calculations confirmed charge transfer from the central aniline unit to the side aryl groups through the sulfonyl bridges, which together indicated the push–pull effect with an extended π‐conjugated system comprising the 2,6‐bis(arylsulfonyl)aniline unit. Furthermore, 2,6‐bis(2‐aminophenylsulfonyl)aniline, with rotatable amino groups at the flanking aryl units, was affected by fluorescence quenching in solution. This nonemissive state showed an enhanced environmental sensitivity to solvent polarity and viscosity, along with a “turn‐on” fluorescence response in frozen solvent and in the aggregated form. 2,6‐Bis(2‐aminophenylsulfonyl)aniline behaved as a turn‐on fluorescence probe for selective detection of DNA based on its aggregation‐induced emission.

2,5‐Dimethoxybenzene‐1,4‐dicarboxaldehyde: An Emissive Organic Crystal and Highly Efficient Fluorescent Waveguide

“…Kim's group designed efficient room temperature phosphorescent crystals based on benzene having alkoxy, aldehyde and bromine groups [unsymmetric, MW=385, HCOBr] . Katagiri's group reported 2,6‐bis(arylsulfonyl)anilines [symmetry, MW >374, HCNOS] as efficient emitters based on single‐benzene framework . Blue emitter of 2,6‐bis(methylsulfonyl)aniline [symmetry, MW=249, HCNOS] and bluish green emitter 2,5‐bis(methylsulfonyl)‐1,4‐diaminobenzene [symmetry, MW=264, HCNOS] was also reported by Katagiri's group .…”

“…Another desirable feature of the emitting molecules is that they possess simple and small structures that allow broadening the scope of their applications. Therefore, single‐benzene molecules have recently attracted considerable attention as rigid and simple frameworks for its use in emitting organic material . For the development of emitters that retain the advantages of the hexagonal structure, a single‐benzene molecule should be designed, which should be characterised by ( i ) a symmetric structure, ( ii ) low molecular weight (MW) and ( iii ) a small number of different constituting atoms.…”

“…Shimizu and Hiyama's group reported low MW molecules based on a single‐benzene framework with π‐expanding vinylene moiety, 1,4‐bis(alkenyl)‐2,5‐dipiperidinobenzenes [symmetry, MW>296, HCN+O or F], for highly efficient solid emitters (Scheme a) . On the other hand, the expansion of the π‐system was shown not to be essential for the low‐energy emission, which was achieved with molecules based on functionalized benzene without conjugated substituents (Scheme b–e) . Kim's group designed efficient room temperature phosphorescent crystals based on benzene having alkoxy, aldehyde and bromine groups [unsymmetric, MW=385, HCOBr] .…”

Tuning the Optical Properties of Sulfonylaniline Derivatives: Degeneracy Breaking of Benzene Orbitals and Linkage through Nodal Planes

“…Therefore, an asymmetric arrangement of electron donors or acceptors is necessary to disrupt the orbital degeneracy of benzene to generate a nodal plane. In this study, based on our previous concept of a push‐pull system between amino and sulfonyl moieties, 2,6‐bis(methylsulfonyl)aniline (BMeSA) exhibits an asymmetric HOMO‐LUMO distribution (Figure a), in which the HOMO is located at the 1‐ and 4‐positions, while the LUMO, which is located at a different position, instead, generates a nodal plane through the atoms at the 1‐ and 4‐positions. BMeSA‐Ar 1 a – d (Figure b), which are π‐extended derivatives at the 4‐position of BMeSA, exhibit HOMO‐dependent tuning of the optical properties, a large dipole moment in the excited state, and positive solvatochromism in fluorescence spectra with a large Stokes shift based on asymmetric molecular orbital distribution and linkage through the nodal plane.…”

Single Benzene Green Fluorophore: Solid‐State Emissive, Water‐Soluble, and Solvent‐ and pH‐Independent Fluorescence with Large Stokes Shifts

“…[10] This observation prompted us to explore more effective combinations of amino and sulfonyl moieties demonstrating longer wavelengths and smaller sizes.T he 1,4-diaminobenzene unit is one of the strongest donating groups with ahigh HOMO and is used as ac omponent in conductive polymers; [11] 1,4-bis(alkenyl)-2,5dipiperidinobenzenes have been reported as visible fluorophores; [12] 2,5-bis(phenylsulfonyl)-1,4-diaminobenzene has been reported as ay ellow crystalline compound. [10] This observation prompted us to explore more effective combinations of amino and sulfonyl moieties demonstrating longer wavelengths and smaller sizes.T he 1,4-diaminobenzene unit is one of the strongest donating groups with ahigh HOMO and is used as ac omponent in conductive polymers; [11] 1,4-bis(alkenyl)-2,5dipiperidinobenzenes have been reported as visible fluorophores; [12] 2,5-bis(phenylsulfonyl)-1,4-diaminobenzene has been reported as ay ellow crystalline compound.…”