Polarized absorption spectra of highly oriented two-dimensional aggregates of tetrachlorobenzimidazolocarbocyanine in thin films

Özçelik, Serdar; Gülen, Demet

doi:10.1016/j.jlumin.2007.11.023

Cited by 2 publications

(1 citation statement)

References 9 publications

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“…In fact, the present type I spectrum of TTBC aggregates has been explained by assuming a 2D flat herringbone structure of transition dipole moments in a phenomenological model by Gülen and co-workers. 33 , 36 At that time, no information from TEM was available, which later revealed a tubular structure of the aggregate, 30 as discussed above. Here, based on our assumption of a crystal-like arrangement, we want to find out whether a tubular herringbone structure can also explain the optical spectra and if such a structure is stable.…”

Section: Introductionmentioning

confidence: 99%

Structure Prediction of Self-Assembled Dye Aggregates from Cryogenic Transmission Electron Microscopy, Molecular Mechanics, and Theory of Optical Spectra

et al. 2016

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Cryogenic transmission electron microscopy (cryo-TEM) studies suggest that TTBC molecules self-assemble in aqueous solution to form single-walled tubes with a diameter of about 35 Å. In order to reveal the arrangement and mutual orientations of the individual molecules in the tube, we combine information from crystal structure data of this dye with a calculation of linear absorbance and linear dichroism spectra and molecular dynamics simulations. We start with wrapping crystal planes in different directions to obtain tubes of suitable diameter. This set of tube models is evaluated by comparing the resulting optical spectra with experimental data. The tubes that can explain the spectra are investigated further by molecular dynamics simulations, including explicit solvent molecules. From the trajectories of the most stable tube models, the short-range ordering of the dye molecules is extracted and the optimization of the structure is iteratively completed. The final structural model is a tube of rings with 6-fold rotational symmetry, where neighboring rings are rotated by 30° and the transition dipole moments of the chromophores form an angle of 74° with respect to the symmetry axis of the tube. This model is in agreement with cryo-TEM images and can explain the optical spectra, consisting of a sharp red-shifted J-band that is polarized parallel to to the symmetry axis of the tube and a broad blue-shifted H-band polarized perpendicular to this axis. The general structure of the homogeneous spectrum of this hybrid HJ-aggregate is described by an analytical model that explains the difference in redistribution of oscillator strength inside the vibrational manifolds of the J- and H-bands and the relative intensities and excitation energies of those bands. In addition to the particular system investigated here, the present methodology can be expected to aid the structure prediction for a wide range of self-assembled dye aggregates.

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Section: Introductionmentioning

confidence: 99%

Structure Prediction of Self-Assembled Dye Aggregates from Cryogenic Transmission Electron Microscopy, Molecular Mechanics, and Theory of Optical Spectra

et al. 2016

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Supramolecular Structure of TTBC J-Aggregates in Solution and on Surface

Berlepsch

Böttcher

2013

Langmuir

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The aggregation behavior of cationic 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidacarbocyanine with chloride (TTBC-Cl) or iodide counterions (TTBC-I) in aqueous solution is investigated by absorption, linear dichroism, and fluorescence spectroscopies, as well as cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). TTBC-Cl is found to form J-aggregates with a classical Davydov-split absorption band (type I spectrum) even under different preparation conditions. These aggregates remain stable for months. Unlike the chloride salt, the iodide salt TTBC-I forms two different types of J-aggregates depending on the pH of the aqueous solution. The TTBC-I aggregates prepared in pure water (pH = 6) are characterized by a single redshifted absorption band (type III spectrum), whereas those prepared in alkaline solution at pH = 13 show a typical Davydov-split (type I) absorption band. Despite differences in counterions, preparation method, stability, and spectroscopic behavior, cryo-TEM reveals an identical tubular architecture for all these J-aggregates. Among the new structure models discussed here is a cylindrical brickwork layer of dye molecules for single-banded J-aggregates (type III). For Davydov-split aggregates (type I), a molecular herringbone-like pattern is proposed instead. Moreover, absorption spectra have revealed an additional single redshifted absorption band (type II spectrum) that is assigned to a surface aggregate and is induced by a specific interaction of the dye cation with the negatively charged cuvette wall. AFM measurements of analogous preparations on negatively charged mica surfaces have supported this interpretation and revealed the formation of monolayered sheet structures.

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Polarized absorption spectra of highly oriented two-dimensional aggregates of tetrachlorobenzimidazolocarbocyanine in thin films

Cited by 2 publications

References 9 publications

Structure Prediction of Self-Assembled Dye Aggregates from Cryogenic Transmission Electron Microscopy, Molecular Mechanics, and Theory of Optical Spectra

Structure Prediction of Self-Assembled Dye Aggregates from Cryogenic Transmission Electron Microscopy, Molecular Mechanics, and Theory of Optical Spectra

Supramolecular Structure of TTBC J-Aggregates in Solution and on Surface

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