Spectroscopic study of squaraines as protein-sensitive fluorescent dyes

Squaraine Compounds: Tailored Design and Synthesis towards a Variety of Material Science Applications

“…They concluded that both the symmetrical and unsymmetrical squarylium dyes show enhancement of fluorescence intensity upon noncovalent interactions with proteins such as HSA, β-lactoglobulin A and trypsinogen. More recently, Yarmoluk et al [61] synthesized and evaluated structureproperties relationships in the series of 3-oxo-and 3-dicyanomethylene squaraines containing indolenine, benzothiazole and benzoxazole moieties 67-68 for detection of a variety of proteins such as bovine BSA, HSA, ovalbumin, avidin from hen egg white (AVI), and hydrolases such as trypsine and lysozyme (Scheme 20). Scheme 20. All of the investigated squaraines show considerable emission quantum yield enhancement in the presence of BSA only; fluorescence enhancing of the dyes in the presence of other albumins (HSA and ovalbumin) is significantly lower, while in the presence of hydrolases lysozyme or trypsin squaraines either insignificantly increased or even decreased their fluorescence intensity.…”

“…Squaraine dyes are generally not soluble in water, their solubility has been thus increased upon suitable functionalization with polar functional groups. In particular, the sulfonate group, [51,61] carbohydrates, [66] quaternary ammonium groups, [50] the carboxy group, [50] polyethylene glycol residues, [24,34,43,44] hydroxy groups, [67] and the phosphonic group. [68] Other strategies take advantage of the strong affinity of some squaraines (i.e., trihydroxybenzene-based squaraines) with BSA [67] and of the synthesis of cholesterol conjugated dyes to enhance cell permeability and perform their photodynamic effect.…”

Dicyanovinyl and Cyano-Ester Benzoindolenine Squaraine Dyes: The Effect of the Central Functionalization on Dye-Sensitized Solar Cell Performance

“…The synthesis of VG2 and VG11 consists of a condensation reaction between a dicyanovinyl substituted squaric acid derivative 1 and a quaternarized indolenine 3 or benzoindolenine 4 to get the aforementioned squaraines. If the synthetic procedure for the dicyanovinyl substituted squaraines is a well-established method [13,19,20] which has been recently improved by microwave irradiation [18], the synthetic pathway to obtain the two cyano-ester dyes is a modification of what has been reported in literature for similar central functionalized squaraines [16,17,21]. The complete synthetic procedures are reported in Figure S1 (Supplementary Materials) as well as 1 H NMR of intermediates 1 and 2 and of the four squaraines which are reported in Figures S2-S7 (Supplementary Materials).…”

Fluorescent Dyes Used in Polymer Carriers as Imaging Agents in Anticancer Therapy

“…Therefore, different NIR dyes as squaraines [91] (i.e., bis(3,5-diiodo-2,4,6-trihydroxyphenyl)squaraine) that emit in the "optical window of tissue" at wavelengths above 800 nm in aqueous solution was assessed in PDT therapy. Squaraine derivatives consist of an oxocyclobutenolate core with aromatic or heterocyclic components at both ends of the molecules [92]. The bis-squaraine dye in which two squaraine units are bridged by a phenyl, biphenyl, thiophene or pyrene spacer exhibit fluorescence enhancements with red emissions in trizma buffer and present noncovalent labeling of human serum albumin (HSA) or bovine serum albumin (BSA) [93].…”