Fluorescence Modulation in Tribranched Switchable [4]Rotaxanes

Abstract

Two novel tribranched [4]rotaxanes with a 1,3,5-triphenylene core and three rotaxane arms have been designed, synthesized, and characterized by (1)H and (13)C NMR spectroscopies and HR-ESI mass spectrometry. [4]Rotaxanes 1 and 2 each possess the same three-armed skeleton. Each arm incorporates two distinguishable binding sites for a dibenzo[24]crown-8 ring, namely a dibenzylammonium site and an N-methyltriazolium site, and is terminated by a 4-morpholino-naphthalimide fluorophore as a stopper. [4]Rotaxane 1 has three di-ferrocene-functionalized dibenzo[24]crown-8 rings whereas 2 has three simple dibenzo[24]crown-8 rings interlocked with the thread component. Uniform shuttling motions of the three macrocycles in both 1 and 2 can be driven by external acid-base stimuli, which were confirmed by (1)H NMR spectroscopy. However, [4]rotaxanes 1 and 2 show distinct modes of fluorescence modulation in response to external acid-base stimuli. [4]Rotaxane 1 exhibits a remarkable fluorescence decrease in response to the addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base, which can displace the ferrocene-functionalized macrocycle from the dibenzylammonium station to the N-methyltriazolium station. In contrast, the fluorescence intensity of [4]rotaxane 2 showed an enhancement with the addition of DBU. Time-resolved fluorescence measurements have been performed. The different photoinduced electron-transfer processes responsible for the fluorescence changes in the two molecular systems are discussed. Topological structures of this kind have significant potential for the design and construction of large and complex assemblies with controllable functions.

A Perylene‐Bridged Switchable [3]Rotaxane Molecular Shuttle with a Fluorescence Output

“…First, we analyzed the 1 H NMR spectrum of [3]rotaxane 2‐H (Figure 1 a). Compared with our previously synthesized rotaxanes,9b, d, 12c, 14b the 1 H NMR spectrum of [3]rotaxane 2‐H revealed that the DB24C8 macrocycles predominately resided on the DBA recognition sites in rotaxane 2‐H . What’s more, compared with the 1 H NMR spectrum of rotaxane 2‐H (Figure 1 a), there was a new peak of H15 at δ =4.33 ppm in the rotaxane 1‐H (Figure 1 b) because of the methylation of the triazole unit.…”

Development and advancement of rotaxane dendrimers as switchable macromolecular machines

“…4). 45 Another tetrapodal [5]rotaxane 18 was reported by Qu using the same di-ferrocene-linked DB24C8 with the simple 3,5-dimethoxyl stopper while the core was the Zn(II) porphyrin (Fig. 4).…”

A Ferrocene‐Functionalized Bistable [2]Rotaxane with Switchable Fluorescence

“…With further research for switchable rotaxane‐containing fluorophores, ferrocene‐modified rotaxane attracted more and more attention 10f. g, k–m A pyrene/ferrocene‐based [2]rotaxane with a three‐level luminescent response was reported by Mateo‐Alonso et al.,10f and a ferrocene‐functionalized molecular shuttle was constructed by Qu and co‐workers, in which the fluorescence of the rotaxane can be reduced or enhanced alternately by an adjustable photoinduced electron transfer (PET) process occurring between two ferrocene (Fc) units in the macrocycle and two fluorescent stoppers 10l. However, it is still a challenge to construct systems in which the shuttling motion of the macrocycle is accompanied with different fluorescence responses, and surely this system would pave the way for constructing more complicated and delicate multilevel molecular switches with optical signals.…”