Cyanine and Squaric Acid Metal Sensors

Lewis Acid Catalyzed 4π-Electrocyclization of Donor–Acceptor Stenhouse Adducts

“…10 Apart from examining the visible-light-induced cyclization of DASA, we questioned the sensitivity of the Stenhouse Adducts to the presence of acid and its potential influence on reversibility. Furthermore, the possible use of a Lewis acid with an asymmetric ligand opens up possibilities for controlling torquoselectivity in the electrocyclization process, 11 12 leading to the formation of enantiomerically enriched cyclopentenones with contiguous stereocenters, which are highly valuable building blocks. 13,14 While the use of stoichiometric amounts of Brønsted–Lowry acid to obtain the ring isomer of DASA has been demonstrated by the Šafář group, 15 DASA’s behavior in the presence of Lewis acids remains unexplored.…”

Near‐Infrared Fluorophores Based on Heptamethine Cyanine Dyes: From Their Synthesis and Photophysical Properties to Recent Optical Sensing and Bioimaging Applications

“…Moreover, small Stokes shift (less than 30 nm) compounds tend to present poor signal‐to‐noise ratio and self‐quenching processes [65–67] . In this context, heptamethine cyanine‐based sensors have been used to detect a variety of cations and anions [68,69] . For instance, to detect the Hg 2+ ions in aqueous solutions, Zheng et al [70] .…”

“…[65][66][67] In this context, heptamethine cyanine-based sensors have been used to detect a variety of cations and anions. [68,69] For instance, to detect the Hg 2 + ions in aqueous solutions, Zheng et al [70] designed a fluorescent ratiometric heptamethine cyanine dye (57) containing a thymine group (T), which binds to the Hg 2 + ion to form a 2 : 1 57 : Hg 2 + complex (Figure 3a). As shown in the absorbance spectra (Figure 3b), the solution of 57 alone exhibited an absorption maximum at 628 nm.…”

“…Heptamethine cyanine dyes can also be used to detect formaldehyde (FA). Wei et al [80] developed a colorimetric sensor (69) to rapidly detect FA in weakly acidic environments based on a heptamethine cyanine dye substituted with a piperazine moiety and a primary amine. In this approach, heptamethine cyanine was used as the chromophore, piperazine was used to respond to pH, and the amine group was used to respond to FA.…”

Synthesis and Characterization of Newly Designed and Highly Solvatochromic Double Squaraine Dye for Sensitive and Selective Recognition towards Cu2+

“…The journey of the squaraine dyes started with the report on the synthesis of squaraine dye by condensation of electron-deficient squaric acid with electron-donating pyrrole units by Triebs and Jacob [ 10 ]. This geared the momentum of research for the development of such a class of intensely colored dyes utilizing vastly available electron-donating aromatic rings and squaric acid [ 11 , 12 , 13 , 14 ]. This quest for the design and development of novel squaraine dyes started about six decades ago, which is expected to be continued in future owing to the plethora of technological applications in the area of probes for bioimaging [ 15 , 16 ], semiconducting elements for organic field-effect transistors [ 4 , 5 ], next-generation solar cells such as organic thin film, dye-sensitized and perovskite solar cells [ 17 , 18 ], huge circular dichroism [ 19 ], and fluorescence based electrofluorochromic devices [ 20 , 21 ] along with diverse applications in sensing assisted by molecular self-assembly controlled guest-host interactions [ 22 , 23 , 24 , 25 , 26 ].…”