H-Aggregates of an Indocyanine Cy5 Dye: Transition from Strong to Weak Molecular Coupling

Abstract

The aggregation behavior of an Indocyanine Cy5 dye (2-[5-[1,1-dimethyl-3-(4-sulfobutyl)-1,3-dihydro-benzo[e]indol-2-ylidene]-penta-1,3-dienyl]-1,1-dimethyl-3-(4-sulfobutyl)-1H-benzo[e]indolium hydroxide, inner salt, sodium salt) in aqueous solution is investigated using absorption and fluorescence spectroscopies, as well as cryogenic transmission electron microscopy (cryo-TEM). The dye concentration is varied within a broad range from ∼1 μM to ∼10 mM. At moderate concentrations, typical H-aggregates are formed. After longer storage time, the absorption spectra of these solutions change dramatically. The characteristic blue-shifted absorption band at around 600 nm becomes replaced by a three-banded absorption spectrum, which spreads over a wide wavelength range of ∼600 up to 800 nm. However, at the highest dye concentration and in the presence of ∼(10 to 30) mM NaCl, the three-banded spectrum is observed directly after preparation. The spectroscopic features can be ascribed to a structural transformation of strongly to weakly coupled H-type aggregates. The transformation is promoted by an increase of the ionic strength. Cryo-TEM data reveal that the weakly coupled H'-aggregates are organized in well-ordered, extended monolayer sheets, whereas the strongly coupled H-aggregates appear to consist of particles of only a few nanometers in size.

Steric‐Structure‐Dependent Gel Formation, Hierarchical Structures, Rheological Behavior, and Surface Wettability

“…The gel samples were measured by smearing the gel onto a quartz slide. Gelator GC (10 −4 m ) in DMF and ethyl acetate gave absorption band centered at λ =260 and 245 nm, respectively, which was related to a π–π* transition (Figure a). The J‐type aggregation of GC molecules in DMF and ethyl acetate was inferred by comparison of the absorption spectra in the solution and gel states .…”

Development of a Modular Ratiometric Fluorescent Probe for the Detection of Extracellular Superoxide

“…All these findings suggest that coupling the (hydro)cyanines to a macromolecule may influence the fluorescence properties and/or sensing ability and may account for the reduced sensing capacity and a high LOD (3.5 and 15.3 μ m ) compared to other examples in literature (80–90 n m ) . However, cyanines are also known to form H‐aggregates in water and buffer especially at higher concentrations, which may also occur with hydrocyanines and alter their sensing behavior . What is worth noting is that, in the cell assays, the increase in the fluorescent signal obtained with our ratiometric probe was in the same order of magnitude as that reported with the commercially available HCy5 (ROSStar™ 650) .…”

“…[26,27,43,23] However,c yanines are also known to form H-aggregates in water and buffer especially at higherc oncentrations, which may also occur with hydrocyanines and alter their sensing behavior. [44] What is worth noting is that, in the cell assays,t he increase in the fluorescent signal obtained with our ratiometric probe was in the same order of magnitude as that reported with the commercially availableH Cy5 (ROSStar 650). [45] This seems to indicate that the switch-onresponse of unconjugated HCy5 is highly influenced by experimental settings and needs carefully controlled conditions to obtain reliable read-outs.…”

Near-Infrared-Fluorescent Erythrocyte-Mimicking Particles: Physical and Optical Characteristics

“…This sandwich-like, - stacking of individual ICG molecules results in interaction of the individual transition dipole moments that raises the excited-state energy to produce a blueshifted absorption peak [49,73,74]. In water, even relatively low concentrations of ICG (> 10 M) will begin to form Haggregates [74,85].…”