Discovery and early development of squaraine rotaxanes

Gassensmith, Jeremiah J.; Baumes, Jeffrey M.; Smith, Bradley D.

doi:10.1039/b911064j

Cited by 214 publications

(170 citation statements)

References 88 publications

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“…This effect is a result of kinetic protection against proton abstraction from the ammonium moiety by the crown ether wheel, which acts as a surrounding "bulky" group that suppresses neutralization by a base. [17] In the neutralization of ammonium salts in organic solvents, it seems most likely that neutralization occurs through initial ammonium proton abstraction by a basic nucleophile present in the system, but not through direct dissociation to a proton and free amine, especially in the present system.…”

Section: Resultsmentioning

confidence: 97%

Neutralization of a sec‐Ammonium Group Unusually Stabilized by the “Rotaxane Effect”: Synthesis, Structure, and Dynamic Nature of a “Free” sec‐Amine/Crown Ether‐Type Rotaxane

Nakazono

Takata

2010

Chemistry A European J

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A fifteen-year riddle has been settled: neutralization, the most popular chemical event, of a crown ether/sec-ammonium salt-type rotaxane has been achieved and a completely nonionic crown ether/sec-amine-type rotaxane isolated. A [2]rotaxane was prepared as a typical substrate from a mixture of dibenzo[24]crown-8 ether (DB24C8) and sec-ammonium hexafluorophosphate (PF(6)) with a terminal hydroxy group through end-capping with 3,5-dimethylbenzoic anhydride in the presence of tributylphosphane as a catalyst in 90% yield. A couple of approaches to the neutralization of the ammonium rotaxane were investigated to isolate the free sec-amine-type rotaxane by decreasing the degree of thermodynamic and kinetic stabilities. One approach was the counteranion-exchange method in which the soft counterion PF(6)(-) was replaced with the fluoride anion by mixing with tetrabutylammonium fluoride, thus decreasing the cationic character of the ammonium moiety. Subsequent simple washing with a base allowed us to isolate the free sec-amine-type rotaxane in a quantitative yield. The other approach was a synthesis based on a protection/deprotection protocol. The acylation of the sec-ammonium moiety with 2,2,2-trichloroethyl chloroformate gave an N-carbamated rotaxane that could be deprotected by treating with zinc in acetic acid to afford the corresponding free sec-amine-type rotaxane in a quantitative yield. The structure of the free sec-amine-type rotaxane was fully confirmed by spectral and analytical data. The generality of the counteranion-exchange method was also confirmed through the neutralization of a bisammonium-type [3]rotaxane. The mechanism was studied from the proposed potential-energy diagram of the rotaxanes with special emphasis on the role of the PF(6)(-) counterion.

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Section: Resultsmentioning

confidence: 97%

Neutralization of a sec‐Ammonium Group Unusually Stabilized by the “Rotaxane Effect”: Synthesis, Structure, and Dynamic Nature of a “Free” sec‐Amine/Crown Ether‐Type Rotaxane

Nakazono

Takata

2010

Chemistry A European J

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“…[6] Thus, intensive efforts have been directed toward the development of turn-on fluorescent sensors, which have become mainstream. [7] Among various strategies, the chemodosimeter approach [8] provides good opportunities to design turn-on sensors for transition-metal ions with both high sensitivity and selectivity.…”

Section: Introductionmentioning

confidence: 99%

Convenient and Efficient FRET Platform Featuring a Rigid Biphenyl Spacer between Rhodamine and BODIPY: Transformation of ‘Turn‐On’ Sensors into Ratiometric Ones with Dual Emission

Xiao

Guo

et al. 2011

Chemistry A European J

140

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We have connected a borondipyrromethene (BODIPY) donor to the 5' position of a tetramethylrhodamine (TMR) acceptor to form a high efficiency (over 99%) intramolecular fluorescence resonance energy transfer (FRET) cassette, BODIPY-rhodamine platform (BRP). While the good spectral overlap between the emission of BODIPY and the absorption of TMR was one favorable factor, another feature of this FRET system was the rigid and short biphenyl spacer that favored efficient through-bond energy transfer. More importantly, in this system, the 2'-carboxyl group of the rhodamine unit was preserved for the further modifications, which was as convenient as those carbonyl groups on the original rhodamines without connection to donors. For this reason, BRP is clearly differentiated from the previous ratiometric sensors based on donor rhodamine systems. To illustrate its value as a versatile platform, we introduced typical Hg(2+) receptors into BRP, through convenient one-pot reactions on the 2'-carboxyl group, and successfully developed two ratiometric sensors, BRP-1 and BRP-2, with different spirocyclic receptors that recognized Hg(2+) on different reaction mechanisms. Upon excitation at a single wavelength (488 nm), at which only BODIPY absorbed, both of the FRET sensors exhibited clear Hg(2+)-induced changes in the intensity ratio of the two strong emission bands of BODIPY and rhodamine. It should be noted that these ratiometric Hg(2+) sensors exhibited excellent sensitivity and selectivity Hg(2+), as well as pH insensitivity, which was similar to the corresponding 'turn-on' rhodamine sensors. While both ratiometric probes were applicable for Hg(2+) imaging in living cells, BRP-1 exhibited higher sensitivity and faster responses than BRP-2. Our investigation indicated that on a versatile platform, such as BRP, a large number of highly efficient ratiometric sensors for transition-metal ions could be conveniently developed.

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“…Additionally reported in the first Treibs and Jacob paper was a note that the pyrrolyl squaraines under investigation discoloured in solutions of amines in ethanol [1]. This was the first observation that squaraine dyes are susceptible to attack by strong nucleophiles, with a solution to this problem taking almost 40 years to be reported; in 2004 with the preparation of squaraine rotaxanes [85].…”

Section: The Beginning: the First Three Yearsmentioning

confidence: 99%

Pyrrolyl Squaraines–Fifty Golden Years

Lynch

2015

Metals

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Pyrrolyl squaraines, both dyes and polymers, were first reported in 1965 and since then a fascinating body of work has been produced investigating the chemistry of these interesting molecules. A major aspect of these molecules that makes them so appealing to those researchers who have contributed to this field over the last 50 years is their chemical versatility. In this review, subjects, such as the synthetic history, an understanding of the molecular structure, an overview of the optical properties, a discussion of both the electrical conduction properties, and magnetic properties, plus use of the particles of pyrrolyl squaraines, are presented. Furthermore, previously published results are not just presented; they are in certain cases collated and used to both highlight and explain important aspects of pyrrolyl squaraine chemistry.

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Discovery and early development of squaraine rotaxanes

Cited by 214 publications

References 88 publications

Neutralization of a sec‐Ammonium Group Unusually Stabilized by the “Rotaxane Effect”: Synthesis, Structure, and Dynamic Nature of a “Free” sec‐Amine/Crown Ether‐Type Rotaxane

Neutralization of a sec‐Ammonium Group Unusually Stabilized by the “Rotaxane Effect”: Synthesis, Structure, and Dynamic Nature of a “Free” sec‐Amine/Crown Ether‐Type Rotaxane

Convenient and Efficient FRET Platform Featuring a Rigid Biphenyl Spacer between Rhodamine and BODIPY: Transformation of ‘Turn‐On’ Sensors into Ratiometric Ones with Dual Emission

Pyrrolyl Squaraines–Fifty Golden Years

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