An investigation of squaraines as a new class of fluorophores with long-wavelength excitation and emission (original) (raw)
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Photochemical properties of squarylium cyanine dyes
Photochemical & Photobiological Sciences, 2013
This study presents several new squarylium dyes derived from benzothiazole and benzoselenazole with several structural variations, namely the nature of the heteroaromatic ring and the length of the N,N'-dialkyl groups. Before being investigated in connection with their effect on living cells and/or tissues, these novel compounds were characterized, namely with respect to the determination of their main photophysical parameters. Therefore, a study of the ground state absorption, fluorescence emission (quantum yields and lifetimes) and singlet oxygen generation quantum yields was performed for all the compounds synthesized in order to evaluate their efficiency as photosensitizers. An increase of the alkyl chain length from ethyl to hexyl did not produce a clear change in the fluorescence quantum yields, showing no influence on the photoisomerization process. Heavy atom inclusion (Se instead of S) enhanced the singlet oxygen generation efficiency and decreased the intensity of the fluorescence emission. The external heavy atom effect (I − as a counterion instead of CF 3 SO 3 −) produced a significant increase in the singlet oxygen formation quantum yield (about 20%). Transient absorption studies in aerated and oxygen free samples revealed that the photoisomerization process, which could compete with the triplet state formation for all dyes in solution, is a negligible pathway for the excited state deactivation, in accordance with the rigidity introduced by the squaric ring into the polymethine chain of the dye, both in chloroform and ethanol. However, in the case of the chloroform solution a new transient was detected in air equilibrated solutions, resulting from a reaction of the excited squarylium dye in the singlet state with CHCl 3˙, and assigned to the radical cation (SQ +˙) of the dye.
Analytica Chimica Acta, 2006
A series of ring-substituted squaraines absorbing and emitting in the red and NIR spectral region was synthesized and their spectral and photophysical properties (quantum yields, fluorescence lifetimes) and photostabilities were measured and compared to Cy5, a commonly used fluorescent label. The absorption maxima in aqueous media were found to be between 628 and 667 nm and the emission maxima are between 642 and 685 nm. Squaraine dyes exhibit high extinction coefficients (163,000-265,000 M −1 cm −1 ) and lower quantum yields (2-7%) in aqueous buffer but high quantum yields (up to 45%) and long fluorescence lifetimes (up to 3.3 ns) in presence of BSA. Dicyanomethylene-and thio-substituted squaraines exhibit an additional absorption around 400 nm with extinction coefficients between 21,500 and 44,500 M −1 cm −1 . These dyes are excitable not only with red but also with blue diode lasers or light emitting diodes. Due to the favourable spectral and photophysical properties these dyes can be used as fluorescent probes and labels for intensity-and fluorescence lifetime-based biomedical applications.
Novel quinone cyanine dyes: synthesis and spectral studies
Dyes and pigments, 2002
Novel dimethine, bis dimethine and tetramethine cyanine dyes derived from benzo [4,5-b; 4 0 ,5 0-b 0 ] bis furo, thieno and pyrrolo-4,8-dione were prepared. The electronic visible absorption spectra of the dyes were examined in 95% ethanol. Structural confirmation is carried out by elemental analysis, IR and 1 H NMR spectral data.
The synthesis and characterization of novel, aza-substituted squarylium cyanine dyes
Dyes and Pigments, 2009
Several squarylium cyanine dyes derived from benzothiazole, benzoselenazole and quinoline were synthesised and the central four member ring functionalized by substitution of one of the oxygen atoms by benzylamine, aniline, 3-iodoaniline, N,N-dimethylhydrazine and 2-aminosulfonic acid groups. All of the ensuing, novel aza-substituted dyes displayed strong absorption within the range 651-709 nm.
Fluorescence lifetime properties of near-infrared cyanine dyes in relation to their structures
Journal of Photochemistry and Photobiology A: Chemistry, 2008
Structurally diverse near-infrared (NIR) absorbing polymethine dyes were prepared and their fluorescence lifetimes (FLT) were evaluated in relation to their structural features. Comparative FLT analysis based on the modification of methine chain length and heterocyclic system showed that indolium or benz[e]indolium heptamethine dyes exhibited longer FLT than the benz[c,d]indolium trimethine dye. Modification of heterocyclic system alone with an intact chain length showed that indolium-based heptamethine dyes showed approximately 30% longer FLT than the benz[e] indolium-based dyes. In general, the FLT of polymethine dyes increased from polar to non-polar solvents. In addition, correlation study between the theoretical and the experimental FLT for indocyanine green (ICG) suggests that the lack of structural rigidity for these cyanine dyes is primarily responsible for the loss of the excited state energy via non-radiative pathway.
SYNTHESIS OF CYANINE DYES CONTAINING QUINOLINIUM HALIDE AND INVESTIGATION OF FLUORESCENCE PROPERTIES
In this study, seven synergists were prepared to improve the contrast ratio in blue color filters derived from cyanine by quenching fluorescence. Improving contrast ratio of LCD color filters, therefore, requires the use of the colorant that can quench the fluorescence without also influencing the color. The colorant must also to be soluble in commercial solvent and stable on typical thermal conditions in the manufacturing process. Four synergists, were prepared in this study, they had absorption maxima of approximately 570~620nm and quenched fluorescence by more than 24%. The synergists increased the contrast ratio by about 30%, due to effective quenching of the fluorescence from the blue color filter, without changing the chromaticity diagram values.