Aggregation of 1,1'-diethyl-2,2'-cyanine chloride as studied by nuclear magnetic resonance

Abstract

The dye, l,l'-diethyl-2,2'-cyanine chloride, was studied in aqueous solution using Fourier transform proton magnetic resonance. The concentration dependencies of the chemical shifts for several different dye protons were determined over a concentration range of 2 X 10-2 to 3 X 10-5 M. All resonances shifted to higher applied field as dye concentration increased, establishing an aggregate structure in which dye molecules stack face to face with considerable overlap of the quinolinium ring system. In dilute solutions where only a monomer <=> dimer equilibrium occurs, the nmr data are interpreted in terms of "ring-current" theory and a dimer model that leads to Kb ~1X 103 M ~l. At higher concentrations, greater degrees of aggregation occur, which, by 2 X 10~2 M, shift dye aromatic protons -0.36 ppm compared with the monomer values. This shift change is interpreted in terms of a polymer composed of units similar to the dimer. Little specific evidence for any unique J-aggregate structure could be obtained. In D2O solutions, the methinyl proton was replaced slowly by deuterium and the rate was studied from pD 7 to 10.6. A rate constant for the acidcatalyzed process of 5 X 102 M~1 sec-1 was found for dye solutions at zero ionic strength.

Reactivity of tetrahydrochromeno[2,3‐b]indoles: chromic indicators of cyanide

“…For comparison, we synthesized 2‐nitro‐5a,6,6‐trimethyl‐5a,6‐dihydro‐12 H –indolo[2,1b][1,3]benzoxazine ( OX , R 2 = CH 3 , R 3 = H) 3 and observed H/D exchange under similar conditions consistent with proposed mechanism. H/D exchange has also been observed in similar systems such as indolospiropyrans and 1,1’‐diethyl‐2,2’‐cyanine chloride …”

Beyond the Cyanine Limit: Peierls Distortion and Symmetry Collapse in a Polymethine Dye

“…No new absorption bands were observed as the concentration increased. The proton chemical shifts of this molecule also showed no concentration-dependent changes associated with significant aggregation of DPy13 .…”

Investigation of two cyanine dyes at normal and high pressure by UV/Vis spectroscopy

“…This blue-shifted spectrum is commonly assigned to H-aggregates, which are most often speci-Ðed as dimers. 28,29,45 Further increases of concentration drastically alter the spectra. In the case of PIC, a very sharp absorption band appears, red-shifted to the monomer peak.…”