Elsevier

Dyes and Pigments

Volume 184, January 2021, 108652
Dyes and Pigments

Dynamic dye emission ON/OFF systems by a furan moiety exchange protocol

https://doi.org/10.1016/j.dyepig.2020.108652Get rights and content

Highlights

  • Four triphenylamine-based dyes were synthesized by a Diels-Alder strategy.

  • A blue light-emitting, high quality single crystal was obtained.

  • The reversibility of the Diels-Alder cycloaddition was used to modulate fluorescence.

  • The α-Position furan-substituted dye was converted into more stable β-position furan-substituted dye by furan moiety exchanges.

Abstract

Four triphenylamine-based dyes were synthesized by fluorescence turn on reactions. Optical behaviours, molecular arrangements, donor-to-acceptor charge transfer and dipole interactions of these functional dyes were investigated by UV–vis absorption and fluorescence spectroscopy, single-crystal X-ray diffraction and electrochemical cyclic voltammetry. The irreversible isomerization of itaconimide dye leads to an irreversible emission switch ON to OFF. Reversible Diels-Alder reaction of these dyes lead to a reversible emission switch OFF/ON. These luminescent dyes demonstrate dynamic dye molecular features by furan moiety exchanges to form energy-minimized and optimized dye molecular structures. In the dynamic molecular system, α-position furan-substituted dye was converted into more stable β-position furan-substituted dye according to 1H NMR spectroscopic monitoring.

Introduction

Reversible cleavage and reformation of covalent bonds are the most interesting features of dynamic covalent reaction, which allow the exchange of molecular moieties at equilibrium to achieve thermodynamic minimum of system [[1], [2], [3], [4], [5]]. Compared with supramolecular weak non-covalent bonds [[6], [7], [8], [9]], dynamic covalent bonds are more robust with response for the environments including temperature, light, mechanical stress, magnetic and electrical fields [[10], [11], [12]]. By dynamic covalent reactions, chemists have prepared a wide range of fascinating 1D, 2D and 3D molecular architectures such as polymers [13,14], molecular knots [15], covalent organic frameworks [[16], [17], [18], [19], [20]], and macrocycles [21,22]. Dynamic covalent reactions can be classified into two main reactions, i.e. exchange reactions including ester, disulfide, furan, amine and acetal exchanges, and new dynamic covalent bond formation reactions including aldol reaction, imine condensation and cycloadditions. On the basis of above outstanding dynamic properties, dynamic covalent dye chemistry has shown various applications such as self-healing, renewable and recyclable materials [[23], [24], [25]], chemical sensors [26,27], biomedical [28], gas storage [29,30]. Recently, Zhang and Jin et al. elegantly described recyclable plastics and thermosets based on dynamic covalent bonds [31]. Ji et al. reported self-healable, recyclable, reprocessable liquid crystalline epoxy thermosets and elastomers with dynamic covalent bonds [32]. Summerlin et al. utilized the reversible properties of Diels-Alder reaction to prepare smart materials with morphology transitions [33].

A very interesting class of dynamic covalent reactions is the Diels-Alder [4 + 2] cycloaddition of electron-rich dienes and electron-poor dienophile [34,35]. Diels-Alder furan-maleimide addition reaction can occur at ambient temperature through relatively low activation barriers, which leads to the only slightly exergonic adducts relative to starting compounds, thus allowing the retro-Diels-Alder addition to occur under appropriate conditions. The controllable characteristics for forward and reverse reactivity of furan-maleimide addition enable chemists to create dynamic molecular systems. In this work, we have designed and synthesized four triphenylamine-based dyes. Triphenylamine chromophores were chosen due to their propeller-like molecular structures and functional electron-donating properties for organic photoelectric p-type materials [[36], [37], [38]]. A high quality crystal was obtained, and its single crystal X-ray diffraction reveals the supramolecular assembling structures. The optical properties of these dyes were investigated. In particular, we demonstrate dynamic dye systems with switchable ON/OFF fluorescence behaviours.

Section snippets

Synthesis

1-(4-(diphenylamino)phenyl)-maleimide (Dye 1) was synthesized according to the previously reported procedure [39].

1-(4-(diphenylamino)phenyl)-itaconimide (Dye 2): Itaconic anhydride (0.56 g, 5 mmol) and acetone (10 mL) were added to a 100 mL flask, and the solution was heated to 50 °C. An acetone solution (8 mL) of 4-aminotriphenylamine (0.98 g, 3.5 mmol) was added dropwise to the reaction flask, and the mixture was reacted at 50 °C for 2 h. The reaction mixture was filtered to give yellow

Synthesis and optical behaviours

Four triphenylamine-based dyes 14 (Fig. 1) were synthesized and fully characterized by NMR and IR spectroscopy and high resolution mass spectrometry (HRMS). Dyes 1 and 2 were synthesized from either maleic anhydride or itaconic anhydride, respectively via 5-member ring opening and subsequently closing reactions [40]. The precursor hydrophilic methylbenzenesulfonate chain was synthesized by the esterification reaction of tosyl chloride with diethylene glycol monoethyl ether (Fig. 2a). The

Conclusion

In summary, four triphenylamine-based dyes were synthesized by Diels-Alder cycloadditions. The studies on the optical and electrochemical properties of these dyes revealed the mechanisms of their fluorescence switches. Isomerization reaction of itaconimide dye is irreversible, which leads to an irreversible emission turn OFF behaviours. Diels-Alder reactions of these dyes are reversible, which leads to a reversible emission turn OFF/ON behaviours. Furthermore, we demonstrate the dynamic dye

CRediT authorship contribution statement

Qi Zhang: Data curation, Formal analysis, Investigation. Ying Wang: Investigation, Methodology, Writing - original draft. Junbo Gong: Conceptualization, Funding acquisition, Project administration, Supervision. Xin Zhang: Conceptualization, Supervision, Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

National Natural Science Foundation of China (grant number 21674079 and 21975177) is acknowledged for financial support.

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