Aggregate Formation in Monomolecular Layers of Cyanine Dyes

Steiger, R.; Kitzing, R.; Junod, P.

doi:10.1080/00223638.1973.11737720

Cited by 24 publications

(13 citation statements)

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“…Aggregates have been reported for many cyanine (or merocyanine) dyes, and their formation is usually critically dependent on the structure and orientation of the cyanine molecules within the layer. 30 The J-aggregates (also called Scheibe aggregates) are characterized by a very narrow red-shifted absorption band and a narrow fluorescence band with a small Stokes shift due to the formation of a delocalized excitonic state among the densely packed molecules. 31 Models have been established to obtain the structure of the aggregates from the shift of the absorption band.…”

Section: Introductionmentioning

confidence: 99%

“…The high density of merocyanines in a monolayer may result in the formation of aggregates with new optical properties. Aggregates have been reported for many cyanine (or merocyanine) dyes, and their formation is usually critically dependent on the structure and orientation of the cyanine molecules within the layer . The J-aggregates (also called Scheibe aggregates) are characterized by a very narrow red-shifted absorption band and a narrow fluorescence band with a small Stokes shift due to the formation of a delocalized excitonic state among the densely packed molecules .…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Photosensitive Langmuir−Blodgett Monolayers by in Situ Atomic Force Microscopy and Absorption Spectroscopy

1998

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Photosensitive monolayers containing both an azobenzene and a spiropyran group were prepared by the Langmuir-Blodgett technique. These films displayed a good reproducibility and a high stability extending up to several months in the dark. Large circular domains with a diameter of several micrometers were seen about 3.5 nm above a homogeneous phase. From geometrical considerations and investigations with different ratios of molecules containing the spiropyran and the azobenzene groups, these domains were interpreted as bilayers of mainly spiropyran molecules. The photoisomerization of both the spiropyran and the azobenzene group was performed. After an initial irradiation with ultraviolet light, the spiropyran transformed to merocyanine and subsequently to J-aggregates. The morphological and the optical changes induced by light were investigated by atomic force microscopy and by absorption spectroscopy on the same layer. The growth of J-aggregates was found to be the best explanation for the observed roughening of the circular domains. In situ atomic force microscopy allowed us to follow the spectacular morphological changes as a function of time and of the irradiation. At the beginning, a small upper structure was seen, usually at the edge of a domain. This upper patch spread progressively within the domain. The resulting multibranched shapes were related to a diffusion-limited aggregation process. Ultraviolet and visible light were seen to induce the presence of nucleation points and to stimulate the roughening process. The morphological change of a domain could also proceed slowly in the dark after the photoinduced nucleation.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of Photosensitive Langmuir−Blodgett Monolayers by in Situ Atomic Force Microscopy and Absorption Spectroscopy

1998

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“…Typically the fluorescence of these aggregates occurs at almost the same wavelength as the absorption, which is known as resonance fluorescence. Numerous dyes have been found to form J-aggregates, among which the cyanines, ,− merocyanines, − and squaraines − are the best represented classes.…”

Section: Introductionmentioning

confidence: 99%

Merocyanine Aggregation in Mesoporous Networks

et al. 1996

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Nanocrystalline films of TiO2, Al2O3, and ZrO2 were used as hosts for the merocyanine 3-acetyl-5-(2-(3-ethyl-2-benzothiazolidinylidene)ethylidene)rhodanine (Mc2) to scrutinize templating effects in the accommodation of the dye within their porous network. Composed of interconnected mesoscopic oxide particles and pores, these films are transparent, allowing for a straightforward application of transmission spectroscopy to unravel the optical features of the incorporated dye species. Apart from H-aggregation, the formation of two different types of two-dimensional assemblies was witnessed yielding red-shifted absorption bands which were identified as J-aggregates, one showing Davidov splitting, the other having a single exciton band. The herringbone packing of the dye molecules in the layered structure of Mc2 sodium salt octahydrate single crystals was taken to model the double-banded J-aggregate structure. On mesoscopic hydroxylated TiO2 anatase films, the structure of the Mc2 assemblies is controlled by the texture of the highly porous substrates as well as their surface charge. Furthermore, it responds in a striking fashion to the presence of solvent in the ambient to which the films are exposed. Double-banded (herringbone structure) and single-banded (parallel alignment of the dye) absorption spectra can thus be obtained. The role of solvent is to stabilize one particular aggregate geometry through intercalation into the Mc2 aggregate. Electron injection into TiO2 from both types of J-aggregates is observed. Laser flash photolysis experiments show that energy transfer from the monomer to the J-aggregate is operative prior to charge injection. On hydroxylated Al2O3 and ZrO2 surfaces Mc2 undergoes physisorption and formation of H-aggregates exhibiting a blue-shifted absorption with regard to the monomer spectrum. Contrary to the results obtained for TiO2 substrates, aggregation is hardly influenced by solvent in the ambient. In particular no J-aggregates can be formed on bare Al2O3 and ZrO2 substrates. However, when the porous films are impregnated with concentrated hydroxide solutions, H- as well as J-aggregates are formed in humid air. At high humidity, due to the hygroscopic salt coating, the pores are completely filled with water, leading to the precipitation of the dye molecules forming H-aggregates. At lower humidity an air−water interface builds up within the pores and a double-banded J-aggregate spectrum appears. The spectrum is almost identical to the one measured on Mc2 sodium salt octahydrate single crystals with a layered organic−inorganic structure. Resonance fluorescence originating from the energetically lower exciton band and internal conversion from the higher to the lower exciton band take place.

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“…Since its discovery by Jelly and Scheibe, much attention has been paid to the investigation of aspects of the J aggregate such as the structure, − optical spectrum, , excited state dynamics, − and energy transfer . J aggregates are also found in wide use as photographic materials and are potentially used as nonlinear optical materials , and multiple wavelength optical recording materials …”

Section: Introductionmentioning

confidence: 99%

Two-Dimensional Aggregation of a Long-Chain Thiacarbocyanine Dye Monolayer on Polyanion Subphases

1996

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Two-dimensional aggregation of a long-chain thiacarbocyanine dye 5,5‘-dichloro-3,3‘-dioctadecyl-9-ethylthiacarbocyanine perchlorate in the monolayers on subphases containing different synthetic polyanions were studied. The aggregation process of the dye in the monolayers was followed by the in situ measurement of the absorption spectra of the monolayers. Two J aggregates were observed at 648 and 666 nm in the monolayer on a plain water surface at all the surface pressures. On the subphase containing poly(acrylic acid), sodium (PAA), and poly(vinyl sulfonic acid), potassium salt (PVS) subphases, the J aggregates were formed at relative high surface pressures (15 and 17.5 mN/m, respectively). On the PVS subphase, an H aggregate at 472 nm was also observed at higher surface pressure (>40 mN/m). On the poly(styrenesulfonic acid), sodium salt (PSS) subphase, neither J nor H aggregates were observed even at higher surface pressures. Models were proposed to explain these interactions between the positively charged dye monolayers and polyanions.

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Aggregate Formation in Monomolecular Layers of Cyanine Dyes

Cited by 24 publications

References 0 publications

Investigation of Photosensitive Langmuir−Blodgett Monolayers by in Situ Atomic Force Microscopy and Absorption Spectroscopy

Investigation of Photosensitive Langmuir−Blodgett Monolayers by in Situ Atomic Force Microscopy and Absorption Spectroscopy

Merocyanine Aggregation in Mesoporous Networks

Two-Dimensional Aggregation of a Long-Chain Thiacarbocyanine Dye Monolayer on Polyanion Subphases

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