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

The Exciton Model for Molecular Materials: Past, Present and Future?

In assemblies of identical molecules or chromophores, electronic excitations can be described as excitons, bound electron-hole pairs that can move from site to site as a pair in a coherent manner. The understanding of excitons is crucial when trying to engineer favorable photophysical properties through structuring organic molecular matter. In recent decades, limitations of the concept of an exciton have become clear. The exciton can hybridize with phonon and photons. To clarify these issues, the exciton is discussed within the broader context of the gauge properties of the electromagnetic force.

Pentamethinium salts as ligands for cancer: Sulfated polysaccharide co-receptors as possible therapeutic target

A series of pentamethinium salts with benzothiazolium and indolium side units comprising one or two positive charges were designed and synthesized to determine the relationships among the molecular structure, charge density, affinity to sulfated polysaccharides, and biological activity. Firstly, it was found that the affinity of the pentamethinium salts to sulfated polysaccharides correlated with their biological activity. Secondly, the side heteroaromates displayed a strong effect on the cytotoxicity and selectivity towards cancer cells. Finally, doubly charged pentamethinium salts possessing benzothiazolium side units exhibited remarkably high efficacy against a taxol-resistant cancer cell line.

Fast assembly of cyanine dyes into aggregates onto [6,6]-phenyl C61-butyric acid methyl ester surfaces from organic solvents

Supramolecular agglomerates of organic colorants based on noncovalent interactions are promising candidates for the development of sensors, optoelectronics, lighting, or photovoltaics. However, their fast and defect-free fabrication on large scales using low-cost technologies has proven elusive so far. Here, we introduce a so far unreported mechanism to induce molecular order in cyanine dyes within minutes from organic solvents by self-assembly. Spin coating blends of a cyanine dye and a soluble fullerene derivative ([6,6]-phenyl C(61)-butyric acid methyl ester (PCBM)) from apolar, aprotic solvents leads to phase-separated structures on the micrometer scale. With this superordinated phase structure, adjustment of dye aggregation is possible, leading to novel optical properties of the film emerging from dye self-assembly on the nanometer scale. In the primary process, semiporous PCBM domains act as nucleation sites for H-aggregates. H-aggregates can then be reconstructed into J-aggregates by dissolving PCBM from the film. Unexpectedly, the method even works for sterically hindered cyanine dyes that are known for their reduced tendency to aggregate. Additionally, selective removal of H-aggregates leaves a template of PCBM nanocrystals, onto which cyanine dye monomers readsorb from solution, forming H-aggregates of similar quality.

Spacer-modulated aggregation of the cyanine dye on the vesicles of gemini amphiphiles

A series of gemini amphiphiles (bis(2'-heptadecyl-3'-ethylimidazolium)-1,n-alkane dibromide, abbreviated as Gn, n = 2, 4, 6, 8, 10) was found to form vesicles under ultrasonication in aqueous solution at very low concentration (5 microM), which was confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The adsorption and interaction of a cyanine dye (3,3'-disulfopropyl-4,5,4',5'-dibenzo-9-methyl-thiacarbocyanine triethylammonium salt, abbreviated as MTC) on the vesicles was investigated. It was found that the cyanine dye could exhibit different colors when interacting with the vesicles. The UV-vis spectral measurements revealed the formation of the H or J aggregates of the cyanine dye on the vesicles, which is spacer length dependent: the short spacer length prefers the formation of the H-aggregate, whereas the longer spacer favors the J-aggregate formation. In addition, these aggregates showed different absorption positions from those on the planar films. Furthermore, by mixing the G2 and G10 vesicles in different ways, the selective aggregation of the cyanine dye on the vesicles was realized.

Regulation of Aggregation and Morphology of Cyanine Dyes on Monolayers via Gemini Amphiphiles

The aggregation of dyes is of considerable importance in relating to their functions and applications. In this paper, we have investigated the regulation on the aggregation and morphology of two cyanine dyes, 3,3'-disulfopropyl-4,5,4',5'-dibenzo-9-methylthiacarbocyanine triethylammonium salt (MTC) and 3,3'-disulfopropyl-4,5,4',5'-dibenzo-9-phenylthiacarbocyanine triethylammonium salt (PTC), using a series of gemini amphiphiles (bis(2'-heptadecyl-3'-ethylimidazolium)-1,n-alkane dibromide, abbreviated as Gn, n=2, 4, 6, 8, 10). It has been found that both of the dyes could be adsorbed onto the monolayers of the gemini amphiphiles through the electrostatic and pi-pi interaction and stacked into H- or J-aggregate. The spacer of the gemini amphiphile showed good control over the aggregation of MTC: H-aggregate was favored when gemini amphiphiles with short spacer were applied, while J-aggregation was preferred in the case of longer spacer. Only J-aggregate was observed for PTC on gemini monolayer, regardless of the structure of the gemini amphiphiles. Interesting morphologies were observed for all the gemini/dye complex monolayers. Network structure and nanofibers were formed for the gemini/MTC films transferred below the plateau surface pressure and close to the collapse pressure, respectively. The ability of the complex monolayers to form nanofibers strongly depended on the component amphiphiles, G2>G4>G6, and no nanofibers were observed for G8/MTC and G10/MTC after the collapse. Only squared domains were observed for gemini/PTC monolayers. When both G2 and G10 were mixed, an individual control of the gemini amphiphiles over the aggregation of MTC in the complex monolayers was observed. The relationship among the spacer, dye structure, and aggregation was revealed.

Substitution controlled molecular orientation and nanostructure in the Langmuir–Blodgett films of a series of amphiphilic naphthylidene-containing Schiff base derivatives

Three amphiphilic Schiff bases containing naphthylidene group, N-octadecyl-2'-hydroxy-naphthalenylideneamine (HNOA-1), N-(4'-octadecyloxy)-2'-hydroxy-naphthalenylideneaniline (HNOA-2), and N-(4'-N-octadecylbenzamide)-2'-hydroxy-naphthalenylideneaniline (HNOA-3), were designed and their interfacial assemblies were investigated. These amphiphiles have different substitution groups in the Schiff base moiety. It was observed that HNOA-1, being in lack of second aromatic ring, formed multilayer films at the air/water interface, while the other two compounds, with another aromatic ring and some hydrophilic groups, can be spread as monolayers on water surface. All of Schiff bases could coordinate with Cu(Ac)2 in situ in the spreading films. Both the spreading films from water and aqueous Cu(Ac)2 subphases were transferred onto solid substrates and their surface morphologies as well as molecular packing modes were investigated by a series of methods such as atomic force microscopy, Fourier transform infrared spectra and X-ray diffraction. Depending on the different substitutions, these amphiphiles showed different orientations in the Langmuir-Blodgett films. Particularly, during the process of complex formation at the air/water interface, great conformational change of the alkyl chain was observed for HNOA-2 in comparison with that of other compounds. In addition, nanofiber structures were observed for the Cu(II)-complexed HNOA-1 and HNOA-2 films.

Spacer-Controlled Aggregation and Surface Morphology of a Selenacarbocyanine Dye on Gemini Monolayers

The adsorption and aggregation of a selenacarbocyanine dye (3,3-disulfopropyl-9-methyl-selenacarbocyanine, SeCy) onto Langmuir monolayers of a series of gemini amphiphiles with different methylene spacers were investigated. When the monolayers of the gemini amphiphiles were spread on the dye-containing subphase, the dye could be easily adsorbed and aggregated onto the monolayers through the electrostatic and pi-pi interaction. The dye formed complexes with gemini amphiphiles and stacked as J-aggregates in all the transferred multilayers, regardless of the structure of gemini amphiphiles. However, the surface morphologies of the complex monolayers showed a significant dependence on the spacer length of the gemini amphiphiles and the temperature of the subphase. Nanorods were observed for the complex films with spacer lengths ranged from 4 to 10 methylenes. With the temperature of the subphases increased from 20 degrees C to 30 degrees C, aligned longer nanofibers were formed instead. Although both the gemini amphiphiles and the dye were achiral, strong circular dichroism (CD) signals were observed for the transferred complex films. However, the CD signals could be just opposite in different places of the transferred films, suggesting that a resolved enantiomeric micro/nanostructure coexisted in the films. On the other hand, for the complex film of the dye with the gemini amphiphile of two methylenes spacer, neither CD signal nor ordered surface morphologies were detected in any place of the film although the dye itself stilled formed J-aggregate in the film. It was suggested that regular nanoarchitectures and resolved chiral domains could be observed only when the spacer of gemini amphiphiles is comparative to the distance between the two SO3- groups in the dye.

Organic nanocrystals with tunable morphologies and optical properties prepared through a sonication technique

Nanocrystals with tunable morphologies and optical properties were successfully fabricated from an organic functional low-molecular-weight compound, 2,4,5-triphenylimidazole (lophine), through a sonication technique.