Fluorescent Thienothiophene-Containing Squaraine Dyes and Threaded Supramolecular Complexes with Tunable Wavelengths between 600–800 nm

Abstract

A new family of fluorescent thiophene and thienothiophene-containing squaraine dyes is described with tunable wavelengths that cover the absorption/emission range of 600–800 nm. The deep-red and near-infrared fluorescent compounds were easily prepared by simple synthesis and purification methods. Spectral studies showed that each squaraine was rapidly encapsulated by a tetralactam macrocycle, with nanomolar affinity in water, to produce a threaded supramolecular complex with high chemical stability, increased fluorescence quantum yield, and decreased fluorescence quenching upon dye self-aggregation. Energy transfer within the supramolecular complex permitted multiplex emission. That is, two separate dyes with fluorescence emission bands that match the popular Cy5 and Cy7 channels, could be simultaneously excited with a beam of 375 nm light. A broad range of practical applications is envisioned in healthcare diagnostics, microscopy, molecular imaging, and fluorescence-guided surgery.

Croconaine Rotaxane Dye with 984 nm Absorption: Wavelength‐Selective Photothermal Heating

“…The absorption properties of dyes C1 and C2 and rotaxanes 1 and 2 are listed in Table . The change in absorption maxima from 824 nm for 1 to 984 nm for 2 is even larger than the change observed with the analogous squaraine series . The 30–40 nm red shift in croconaine absorption upon encapsulation by M is consistent with our previous studies .…”

“…The change in absorption maxima from 824 nm for 1 to 984 nm for 2 is even larger than the change observed with the analogous squaraine series. [27] The 30-40 nm red shift in croconaine absorption upon encapsula- tion by M is consistent with our previous studies. [14] As shown by the absorption spectra in Figure 4, the absorption maxima bands for 1 and 2 are quite sharp with little spectral overlap.…”

“…While some croconaine dyes are known with absorption maxima between 900–1000 nm, none have been reported as an interlocked rotaxane . The chemical structure of croconaine C1 has two flanking thiophene units and in a recent study of analogous squaraine dyes, we found that synthetic substitution of the thiophenes with flanking thienothiophene units led to an increase in conjugation and a 100 nm red‐shift in the squaraine absorption maxima band . Equally important, the flanking thienothiophene units still allowed threading of the tetralactam macrocycle M .…”

“…Materials: Commercially available solvents and chemicals were purchased from Sigma‐Aldrich, Alfa‐Aesar, and VWR international and used without further purification unless otherwise stated. Thienothiophene 3 was prepared using a previously reported procedure . Flash column chromatography was performed using a Biotage flash purification system with SNAP Ultra flash chromatography cartridges.…”

“…[15] The chemical structure of croconaine C1 has two flanking thiophene units and in a recent study of analogous squaraine dyes, we found that synthetic substitution of the thiophenes with flanking thienothiophene units led to an increase in conjugation and a 100 nm red-shift in the squaraine absorption maxima band. [27] Equally important, the flanking thienothiophene units still allowed threading of the tetralactam macrocycle M. With this precedence in mind we decided to prepare the new extended croconaine dye C2 and determine if it could be used to thread M and be converted into the new croconaine rotaxane 2. Once 2 was in hand, we wanted to demonstrate wavelength-selective photothermal heating of separate solutions containing either 1 or 2.…”