Fluorescent molecular photoswitch based on basket-shaped porphyrins

https://doi.org/10.1016/j.tetlet.2020.152104Get rights and content

Highlights

  • Two basket-shaped porphyrins strapped by diarylethene was constructed.

  • Their reversible photochromic properties were studied.

  • The photoswitchable fluorescent characteristics have been investigated.

Abstract

Here we present two novel basket-shaped porphyrins bridged by photochromic diarylethene derivatives, which show significant photoswitchable fluorescent properties. Their synthesis, structures, photochromism and fluorescence characteristics were reported in detail. They are desirable for reversible light-driven fluorescent molecular switches.

Graphical abstract

Two novel basket-shaped porphyrin molecules bridged axially by photochromic diarylethene derivatives. Their preparation, structure characterization and photochromism were reported in detail. The reversible photoswitchable fluorescent characteristics have been investigated. This kind of compounds are desirable for reversible light-driven fluorescent molecular switches

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Introduction

Light-driven fluorescent molecular switches have currently attracted great interest in stimuli-responsive materials and molecular opto-electronics [1], [2], [3]. Photochromic diarylethenes have their inherent advantages as photoswitchable molecules due to their high photosensitivity, excellent fatigue resistance and outstanding thermal stability [4], [5], [6], [7]. However, most diarylethene molecules have very weak fluorescence with short emission wavelengths or even no fluorescence, which limited their applications in the longer wave range. Therefore, the complementary designs of diarylethenes and various fluorescent molecules have been developed. Among them, the connection of diarylethenes and porphyrins has attracted considerable attentions. It is well-known that porphyrins are one of the most representative macrocyclic compounds with excellent light stability, thermal stability and photoelectric properties due to their highly aromaticity [8], [9], [10], [11], [12]. They have been widely applied in light-induced electron transfer systems, molecular energy storage devices and photoelectric conversion system based on the strong near-infrared fluorescence, large molar elimination coefficient and long lifetime of excited singlet states [13], [14], [15], [16], [17], [18], [19], [20]. In recent years, our group has carried out a series of studies on the preparation and characteristics of functional porphyrins based on photochromic diarylethenes [21], [22], [23]. There are two main methods to combine diarylethenes with porphyrin groups. On the one hand, porphyrins can be covalently bonded to diarylethylene molecules to form various linear or planar functional molecules [24], on the other hand, diarylethylenes containing coordination groups can be used as ligands to coordinate with the central metal ion of porphyrins to form coordination compounds, which can be further assembled into supramolecular compounds [25]. The two approaches have many promising applications, but the problem of π-π stacking caused by the rigid planar structure of porphyrins and the relatively weak coordination ability between ligands and metal ions need to be solved. Therefore, we further developed binding porphyrins-dithienylethene system [26], in which diarylethylene was axially bonded to the porphyrin ring. This design made the system performing excellent photochemical double-throw switches. However, once ions such as zinc ions were added, it would no longer have photochromic properties, which limited its application as a fluorescent switch in the presence of ions. For this reason, we have improved the molecular design in this paper by incorporating pyridine groups at the meso positions of the porphyrin and two novel basket-shaped porphyrins strapped by diarylethene derivatives (DTE-1o and Zn-DTE-1o) for fluorescent molecular photoswitches were designed and constructed (Scheme 1). Their structures have been confirmed by nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR), high resolution mass spectrometry and single crystal X-ray diffraction. The light-triggered reversible fluorescence emission in the near infrared and photochromism of the diarylethene-porphyrin system was investigated in detail.

Section snippets

Synthesis and structure characterization

The synthetic procedures of basket-shaped porphyrins are shown in Scheme 2. The preparation and characterization of intermediates, diarylethylene and other related compounds (compound 15), were reported in the supporting information in detail. With them in hand, the chlorinated diarylethylene 1 reacted with n-BuLi to give the corresponding borate 2, and further reacted with bromobiphenyl aldehyde 3 via classical Suzuki reaction to obtain diarylethylene dialdehyde 4. DTE-1o was obtained from

Conclusion

In this paper, photochromic diarylethylene was designed to stretch across the two meso positions of macrocyclic porphyrin. The pyridines group were introduced at the other two meso positions of the porphyrin ring to construct two light-driven fluorescent molecular switches. The synthesis, photochromism and fluorescent performances were investigated. The reversible changes in the UV–vis absorption and fluorescence emission spectra of the target molecules before and after photoirradiation were

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.

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