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

Abstract

Benzene is the simplest aromatic hydrocarbon with a six-membered ring. It is one of the most basic structural units for the construction of π conjugated systems, which are widely used as fluorescent dyes and other luminescent materials for imaging applications and displays because of their enhanced spectroscopic signal. Presented herein is 2,5-bis(methylsulfonyl)-1,4-diaminobenzene as a novel architecture for green fluorophores, established based on an effective push-pull system supported by intramolecular hydrogen bonding. This compound demonstrates high fluorescence emission and photostability and is solid-state emissive, water-soluble, and solvent- and pH-independent with quantum yields of Φ=0.67 and Stokes shift of 140 nm (in water). This architecture is a significant departure from conventional extended π-conjugated systems based on a flat and rigid molecular design and provides a minimum requirement for green fluorophores comprising a single benzene ring.

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

“…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.…”

Efficient Red‐Emissive Organic Crystals with Amplified Spontaneous Emissions Based on a Single Benzene Framework

“…In the past decade, organic crystals exhibiting ASE with emission peak in the range of 400 to 600 nm have been achieved. Although single-benzene-based solid emitters,2 ,5-bis(methylsulfonyl)-1,4-diaminobenzene and (2-hydroxyphenyl)propenone derivatives,s howing intense bluish green and green emissions have been reported by Katagirisg roup [7] and our group, [8] respectively,t he realization of highly efficient red-emissive solids based on the single-benzene skeleton without astrong D-A framework is more challenging.T he synthesis,p hotophysical properties, crystal structure,a nd theoretical calculations of the singlebenzene-based compounds 1a-c were carefully studied. [6] Herein, highly efficient red-emissive organic crystals were obtained through an ovel molecular design strategy in which neither polycyclic skeleton nor strong D-A framework was employed ( Figure 1b).…”

A C4N4 Diaminopyrimidine Fluorophore

“…As such, C4N3‐type derivative 4 with an extra phenyl group at the 2‐position had weak fluorescence, whereas C4N2‐type derivatives 2 d and 5 lacking a 5‐amino group were virtually nonemissive. The lack of emission from p ‐phenylenediamine derivative 6 underscored the requirement for concurrent deployment of the pyrimidine unit and 2,5‐diamino groups to produce intense fluorescence …”