The electronic excited states of molecular aggregates and their photophysical signatures have long fascinated spectroscopists and theoreticians alike since the advent of Frenkel exciton theory almost 90 years ago. The influence of molecular packing on basic optical probes like absorption and photoluminescence was originally worked out by Kasha for aggregates dominated by Coulombic intermolecular interactions, eventually leading to the classification of J- and H-aggregates. This review outlines advances made in understanding the relationship between aggregate structure and photophysics when vibronic coupling and intermolecular charge transfer are incorporated. An assortment of packing geometries is considered from the humble molecular dimer to more exotic structures including linear and bent aggregates, two-dimensional herringbone and “HJ” aggregates, and chiral aggregates. The interplay between long-range Coulomb coupling and short-range charge-transfer-mediated coupling strongly depends on the aggregate ...

Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer.

Poly(3,4-ethylenedioxythiophene) nanoparticles prepared in aqueous DBSA solutions

The structures of Langmuir–Blodgett films of fatty acids and their salts

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 t...

Merocyanine Aggregation in Mesoporous Networks

The surfactant-free synthesis of colloidal dispersions of vinyl polymer−silica nanocomposite particles in aqueous media using a batch emulsion polymerization protocol has been previously described [Percy, M. J.; et al. Langmuir 2000, 16, 6913]. In the present work 2-hydroxypropyl methacrylate [HPMA] was copolymerized with 4-vinylpyridine [4VP] using ammonium persulfate in the presence of an ultrafine silica sol. 4VP is used as an auxiliary in these syntheses; the strong interaction of this basic monomer with the acidic surface of the silica particles is essential for successful nanocomposite particle formation. HPMA monomer was selected since it has appreciable water solubility (up to 13% at 20 °C), but HPMA homopolymer is water-insoluble. This unusual solubility behavior ensured that these nanocomposite syntheses were conducted under true dispersion polymerization conditions. In view of the success of these syntheses, we conclude that emulsion monomer droplets and micelles are not a prerequisite for the ...

Synthesis of vinyl polymer-silica colloidal nanocomposites via aqueous dispersion polymerization

Surface morphology and stability of Langmuir-Blodgett mono- and multilayers of saturated fatty acids by scanning force microscopy

Microcrystallinity of solid-state langmuir-blodgett films of saturated fatty acids studied by scanning force microscopy and brewster angle microscopy

A water-soluble metal complex dyad, Rh(III)-X-Ru(II), was incorporated in monolayers at the air/ water interface by cospreading with a positively (eicosylamine) or negatively (stearic acid) charged amphiphile. After transfer of the monolayer onto a mica substrate via the Langmuir- Blodgett technique, a domain structure similar to that at the air/water interface was observed by scanning probe microscopy (SPM). With scanning force microscopy (SFM) we found domains with diameters in the micrometer range protruding several angstroms from the interstitial areas. The same structure was imaged with scanning near-field optical microscopy (SNOM) with joint registration of topographic features and ruthenium fluorescence. We present a model for the complex structure of the molecular film compatible with the different microscopy results.

Scanning force and scanning near-field optical microscopy of organized monolayers incorporating a nonamphiphilic metal dyad

Structural investigation of dipping lines in Langmuir-Blodgett films by scanning force microscopy

Brickstone arrangement in J-aggregates on an amphiphilic merocyanine dye

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