Tuning photosensitized singlet oxygen generation efficiency of novel aza-BODIPY dyes

Novel aza-BODIPY derivatives substituted with heavy atoms such as bromine and iodine were synthesized, and their triplet and singlet oxygen generation efficiencies have been investigated. These derivatives showed absorption in the NIR region with high molar extinction coefficients. The dye substituted with four iodine atoms showed yields of φ<SUB>T</SUB> = 0.78 and φ(<SUP>1</SUP>O<SUB>2</SUB>) = 0.70, which are the highest values so far obtained for the aza-BODIPY derivatives

Dual-mode semisquaraine-based sensor for selective detection of Hg<SUP>2+</SUP> in a micellar medium

A novel chemosensor based on semisquaraine dye (SSQ) for selective detection of Hg2+ is described. SSQ is obtained in quantitative yields from the reaction between squaric acid and 6-ethoxy-2-quinaldinium iodide. SSQ in combination with surfactant shows a dual chromogenic and fluorogenic response selectively toward Hg2+ as compared to Li+, Na+, K+, Ag+, Ca2+, Mg2+, Zn2+, Pb2+, Cd2+, Cu2+, and Fe3+ due to the soft acid nature and size of the mercuric ion

Synthesis of new cholesterol-and sugar-anchored squaraine dyes: further evidence of how electronic factors influence dye formation

Synthesis of new quinaldine-based squaraine dyes linked to cellular recognition elements that exhibit near-infrared absorption ( > 740 nm) are described. Both product analysis and theoretical calculations substantiate the interesting electronic effects of various substituents in the dye formation reaction. These results are useful in the synthesis of symmetrical and unsymmetrical squaraine dyes that can have potential biological and photodynamic therapeutical applications

Infrared absorbing croconaine dyes: synthesis and metal ion binding properties

Quinaldine-based croconaine dyes synthesized by the condensation reaction between croconic acid and the respective quinaldinium salts are described. These dyes exhibit absorption maximum in the infrared region (840-870 nm) with high molar extinction coefficients (1-5 × 105 M−1 cm−1) and have very low fluorescence quantum yields. Upon binding to divalent metal ions, these dyes were found to form complexes with a 2:1 stoichiometry having high association constants of the order of 1011-1014 M−2, while the monovalent metal ions showed negligible affinity. The binding of the croconaine dye 3d with divalent metal ions especially Zn2+, Pb2+, and Cd2+ led to significant chelation-enhanced fluorescence emission. The broadening of the aromatic signals, vinylic and N-methyl protons and the negligible changes at the aliphatic region of the dye 3d in the 1H NMR spectrum in the presence of Zn2+, indicate that the binding occurs at the carbonyl groups of the croconyl ring. The shift in the croconyl carbonyl stretching frequency in the [3d-Zn2+] complex analyzed through FT-IR analysis further confirms the involvement of two electron-rich carbonyl groups of the croconyl moiety in the complexation. These results demonstrate that the binding of the divalent metal ions at the carbonyl oxygens of these infrared absorbing dyes can be favorably utilized for the development of potential sensors for the detection of metal ions and further can be exploited as sensitizers for photodynamic therapeutic applications

Squaraine dyes in PDT: from basic design to in vivo demonstration

The design and development of novel squaraine dyes as sensitisers for photodynamic therapy (PDT) applications has grown tremendously in the last decade from the time when a squaraine dye was proposed to be a potential candidate, to-date when the use of such dyes have been demonstrated in animal models for skin cancer. This perspective article highlights the basic design, tuning of absorption, triplet excited state and two-photon absorption properties and recent developments of the squaraines as PDT sensitisers

β-Cyclodextrin as a photosensitizer carrier: effect on photophysical properties and chemical reactivity of squaraine dyes

With the objective of understanding the utility of β-cyclodextrin (β-CD) as a carrier system, we have investigated its interactions with a few near-infrared absorbing squaraine dyes (i.e., 1a,b and 2a,b) through absorption and steady-state and time-resolved fluorescence techniques. The addition of β-CD to the phloroglucinol dyes 1a,b resulted in a significant bathochromic shift in absorption, together with a ca. 1.5-2.5-fold enhancement in fluorescence intensity, whereas for the aniline-based dyes 2a,b, a hypsochromic shift in the absorption and a ca. 5-12-fold fluorescence enhancement were observed in a 10% (v/v) ethanol/water mixture. Benesi-Hildebrand analysis showed that both the dyes 1a,b and 2a,b form 2:1 stoichiometric complexes with β-CD. The complex formation was confirmed by competitive binding analysis employing adamantyl-1-carboxylic acid (ACA) and adamantyl-1-ammonium chloride (ADAC). The displacement of the dyes 1a,b and 2a,b from the [dye-β-CD] complex by ADAC and ACA unambiguously establishes the encapsulation of these dyes in the hydrophobic nanocavity of β-CD. Uniquely, the formation of the inclusion complexes with β-CD provides unusual protection from nucleophilic attack by aminothiols such as cysteine and glutathione for dyes 1a,b, whereas negligible protection was observed for dyes 2a,b. These results demonstrate the substituent-dependent encapsulation of potentially useful squaraine dyes in β-CD, thereby indicating its potential as a carrier system for the squaraine dyes 1a,b useful in photodynamic therapy

Functional cyclophanes: promising hosts for optical biomolecular recognition

Cyclophanes possess a defined cavity size and are efficient in encapsulating and stabilising guest molecules inside the cavity through various non-covalent interactions. This unique property of the cyclophanes has been widely exploited for the development of selective probes for a variety of guest molecules. The present tutorial review highlights the use of various interesting functionalised cyclophane architectures for the sensitive and selective optical recognition of important biomolecules

Novel semisquaraine regioisomers: isolation, divergent chemical reactivity and photophysical properties

A zwitterionic semisquaraine 1,3-regioisomer which exhibits distinct photophysical properties and chemical reactivity was isolated. Uniquely, this isomer has been identified as the reactive intermediate in the squaraine dye formation reaction rather than the neutral 1,2-isomer and opens up new avenues for the synthesis of novel dyes for optoelectronic applications