Excitation Energy Transfer in Ion Pairs of Polymethine Cyanine Dyes: Efficiency and Dynamics

Spectral-fluorescent and photochemical study of 6,6'-di(benzoylamino)trimethine cyanine dyes in solutions as possible probes for DNA

Spectral-fluorescent and photochemical properties of trimethine cyanine dyes T-304, T-306, and T-307, having substituents in 6,6'-positions, in various organic solvents, in aqueous buffer solutions, in the presence of surfactants and ethanol additives, and the effect on these properties of addition of DNA have been studied. Strong aggregation of the dyes in aqueous and aqueous buffer solutions has been shown. This is due to increased hydrophobicity of the dyes, which makes it difficult to use them as spectral-fluorescent probes for DNA. In the presence of DNA, trimethine cyanines partially form highly fluorescent complexes of dye monomers with the biomolecule, with slight decomposition of the initial aggregates and the formation of aggregates on DNA molecules. The formation of different types of dye-DNA complexes, i.e., intercalation and binding in the DNA grooves, was modeled by molecular docking. Dye-DNA complexes were also studied by circular dichroism spectroscopy and by thermal dissociation of DNA. To reveal selectivity of the dyes, their interaction with human serum albumin was briefly studied. The presence of moderate concentrations of nonionic surfactants does not lead to a significant decomposition of aggregates, but leads to a biphasic dependence of the fluorescence intensity on the DNA concentration. At the same time, ethanol additives (15%) lead to a more or less linear concentration dependence of the fluorescence intensity, which makes it possible to use these dyes as fluorescent probes for DNA. The effective binding constants of the dyes to DNA and the limits of DNA detection using the dyes in the presence of 15% ethanol were estimated. Photoisomerization and generation of the triplet states of T-304, T-306, and T-307 have been also studied. Along with the fluorescence growth, complexation with DNA leads to an increase in the yield of the triplet states of the dyes. This creates a prerequisite for using the dyes in targeted PDT. In the presence of DNA, the decay kinetics of the triplet states are biexponential, which indicates different types of dye complexes with DNA. The rate constants of oxygen quenching of the triplet states of the dyes bound to DNA are significantly lower than the diffusion-controlled values (taking into account the spin-statistical factor), which is explained by the shielding effect on the triplet molecules in complexes with DNA. The data obtained show that dyes T-304, T-306 and T-307, with addition of 15% ethanol, can be used as possible fluorescent probes for DNA.

Maple™-assisted calculations of the J-integral: a key parameter for the understanding of excited state energy transfer in porphyrins and other chromophores

The spectral overlap between the emission of a donor molecule and the absorption of an acceptor molecule, quantifiable using the J-integral calculation, is a parameter of extreme importance when studying the excited state energy transfer by either the Főrster or Dexter mechanism. Despite its extreme importance in both mechanisms, it is often misinterpreted, approximated or incorrectly calculated. The calculation of the J-integral is not trivial especially when one wishes to carry out the calculation on measured spectroscopic data. A detailed description for the correct calculation of the J-integral is herein reported and presents a Maple™ assisted template that is capable of performing this calculation in the two different energy scales (nm and cm-1) to yield the value of the J-integral in given units. Specific examples using porphyrin-containing compounds are provided. This Maple™ program is flexible and can be easily adapted to the needs of a researcher. A call for the standardization of the calculation of the J-integral for the facile comparison with other overlap integrals found in the literature is made.

Controlling the formation of cyanine dye H- and J-aggregates with cucurbituril hosts in the presence of anionic polyelectrolytes

The presence of anionic polyelectrolytes enhances the tendency of cationic cyanine dyes to form aggregates in aqueous media. In this work we investigate the interactions between two cyanine dyes, pseudoisocyanine (PIC) and pinacyanol (PIN), with polystyrenesulfonate (PSS) as the key additive to develop J- and H-aggregates. We also take advantage of the binding properties of the cucurbit[7]uril (CB7) host to control formation of these aggregates through its host-guest interactions with the dye molecules. UV/Vis absorption spectroscopic studies clearly demonstrate the PSS-enhanced formation of J-aggregates in the case of PIC and H-aggregates in the case of PIN. Electrostatic interactions between the cyanine dye molecules and the polyelectrolyte chains assist the formation of J- or H-aggregates at very low dye concentrations (ca. 10 microM). Optimum development of dye aggregates was observed at a sulfonate/dye molar ratio of about 3:1. Departures from this stoichiometric ratio seem to perturb the optimal aggregate structure. Furthermore, the presence of CB7 was found to effectively disrupt the interactions responsible for dye aggregation. Thus, CB7 completely disrupts the J-aggregates formed by PIC and the H-aggregates (as well as lower concentrations of J-aggregates) formed by PIN. UV/Vis and emission spectroscopic studies clearly indicate that binding of CB7 to both dye molecules removes them from the aggregate structures. Our spectroscopic data clearly indicate that regulation of the relative molar ratios of dye, CB7 host, and polyelectrolyte sulfonate groups leads to a quantitative control of dye aggregation, yielding variable amounts of PIC J- and PIN H-aggregates in these solutions.

Control of H- and J-aggregate formation via host-guest complexation using cucurbituril hosts

The binding interactions between two cyanine dyes, pseudoisocyanine (PIC) and pinacyanol (PIN), and the cucurbit[n]uril hosts, cucurbit[7]uril (CB7) and cucurbit[6]uril (CB6), were investigated by electronic absorption spectroscopy and DFT computational methods. The CB7 host forms more stable complexes with both dyes than CB6 and the computational studies suggest that the cavity of the smaller host CB6 is not threaded by the dyes. The equilibrium association constants (K) for complexation by CB7 were measured and found to be 2.05 x 10(4) and 3.84 x 10(5) M(-1) for PIC and PIN, respectively, in aqueous media at 23 degrees C. CB7 complexation was found to effectively disrupt the intermolecular forces responsible for the aggregation of both dyes. Thus, CB7 completely disrupts the J-aggregates formed by PIC and the H-aggregates (as well as lower concentrations of J-aggregates) formed by PIN. In both cases a competing guest, 1-aminoadamantane (AD), could be used to adjust the extent of aggregation of the cyanine dye. AD regulates aggregate formation because it forms an extremely stable complex with CB7 (K approximately = 10(12) M(-1)) and exerts a tight control on the CB7 concentration available to interact and bind with the dye.