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Abstract

We report the photobehaviour of a series of eight structurally related arylacetylene derivatives, in solution as well as in pristine and PC61BM blended thin-_lms. The formation of both H- and J-aggregates in the solid state have been demonstrated, and, interestingly, an energy transfer from H-aggregates or/and from residual "unstacked" molecules to J-aggregates has been found, the latter being the only emitting species. The fuorescence quenching by PC61BM at di_erent loadings has been studied in blend films, and it has been found particularly effcient in the case of a symmetrical peripheral substitution of the acetylene derivative core. Preliminary time-resolved measurements in emission (ns resolution) and in absorption (fs resolution) con_rmed the H⟶J energy transfer and underlined the presence of delayed fuorescence from Jaggregates, formed by energy transfer from the long-lived first excited singlet state of H-aggregates. In all cases, a homogeneous surface morphology of thin films

Abstract

Formamide colloidal suspensions of layered double hydroxides (LDHs) with anionic dye, meso-tetrakis(4-sulfonatophenyl)porphine (TPPS) were prepared. Optical properties of these suspensions were investigated by means of absorption and fluorescence spectroscopies in the visible region. For more detailed characterization, second derivative curves of the spectra were calculated. The adsorption of the dye on LDH nanosheets led to partial molecular aggregation, reflected in significant changes of the dye optical properties. The Soret band in the absorption spectra was split into two peaks and decreased in intensity. Changes were observed also for the Q-bands. The molecular aggregation significantly quenched the emission of the dye. The low intensity emission from dye H-aggregates was identified at slightly longer wavelengths. The molecular aggregation increased with the dye/LDH ratio. At low dye loadings, the optical properties were very similar to the dye solution. The yields of the dye molecular aggregation increased with LDH surface charge.

Abstract

Stopped-flow mixing device and visible absorption spectroscopy were used for the analysis of dye rhodamine 6G (R6G) molecular aggregation in the colloids based on Na-saturated montmorillonite. Two stages of the reaction were identified: The first stage was very short and taking only several seconds, involving the adsorption of R6G cations and their initial aggregation on the surface of colloid particles. The initially formed J-aggregates exhibited similar spectral properties as monomeric form of R6G. In the second stage, initially formed aggregates converted to sandwich-type H-aggregates absorbing light at significantly lower wavelengths and adsorbed monomers. The aggregate rearrangement took several hours. Monomers, with the spectral properties identical to R6G solution, were also identified as a component in complex spectra using principal component analysis (PCA) and multivariate curve resolution (MCR). Partial bleaching of the dye was also proven. Reaction kinetics of the rearrangement of the aggregates followed the model considering a complex mechanism of the molecular aggregation. Data fits using stretched-exponential function led to the determination of rate constants, which had been in the range 10−3−4×10−3s−1.

., Jahre M., Interdependence in supply chains and projects in construction , Supply Chain Management: An International Journal, 15 (5), 2010, 385–393. [8] Lönngren H., Rosenkranz C., Kolbe H., Aggregated construction supply chains: success factors in implementation of strategic partnerships, Supply Chain Management: An International Journal, 15 (5), 2010, 404–411. [9] Vrijhoef R., Koskela L., The four roles of supply chain management in construction , European Journal of Purchasing & Supply Management, Vol.6, 2000, 169–178. [10] Szymczak M., Modele zarządzania

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. Saikin, Alexander Eisfeld, Stéphanie Valleau and Alán Aspuru-Guzik Photonics meets excitonics: natural and artificial molecular aggregates DOI 10.1515/nanoph-2012-0025 Nanophotonics 2013; 2(1): 21–38 Review: This review article estab- lishes a bridge between the fields of photonics and excitonics by describ- ing the present understanding of exciton dynamics in molecular aggregates. Keywords: exciton; exciton dyna- mics; molecular aggregates; J-aggre- gates; H-aggregates; light-harvesting complexes. Photonics Plasmonics 100 nm 10 nm 1 nm Excitonics Peter Lodahl

adsorbierten Aggregate Aus den Reflexionsspektren geht hervor, ob auf der Oberfläche der Silberhalogenidkörner symmetri­ sche H- oder unsymmetrische J-Aggregate vorliegen. Bei Betrachtung der Reflexionsspektren21, 22 kann man zwei Typen unterscheiden. Farbstoffe, die in Lösung ein J-Aggregat bilden (z.B. Pseudoisocya- n in), zeigen auch im Reflexionsspektrum bei allen Farbstoffkonzentrationen, also bei allen Bedeckungs­ graden, eine J-Bande (Abb. 8 A ) . Farbstoffe dage­ gen, die in Lösung H-Aggregate bilden (z.B. Tri- methinthiacyanine), zeigen im Reflexionsspektrum

References 1. A. Rama, K. Selvaraj, and S. Hayase, “Molecular dynamics simulations on the aggregation behavior of indole type or- ganic dye molecules in dye-sensitized solar cells”, J. Mol. Model 18, 2099-2104 (2012). 2. T. Horiuchi, H. Miura, K. Sumioka, and S. Uchida, “High efficiency of dye-sensitized solar cells based on metal- -free indoline dyes”, J. Am. Chem. Soc. 126, 12218-12219 (2004). 3. C. Nasr, D. Liu, S. Hotchandani, and P. Kamat, “Dye-capped semiconductor nanoclusters. excited state and photosensiti- zation aspects of rhodamine 6G H-aggregates

state of the molecules. According to the molecular exciton theory, different aggregation patterns of organic dyes have been proposed. J or H aggregates are usually considered for dye aggregates. In the first state, dipole transitions of both monomer molecules are coupled with each other in the parallel plane, while in the second form, they are placed in the same plane in the form of head to tail [ 3 ]. Hence, solute-solvent and solute-solute interactions can have significant influences on the linear and nonlinear optical properties of molecules. Furthermore, the

dichloromethane solution over clean slides of fused silica have also been investigated in the 200-600 nm spectral range (Fig. 3): they display the typical * and n * electronic transitions of the azoaromatic isolated chromophore centered at around 360 nm and 440 nm, respectively, and an additional band centered at 248, nm associated with the * transition of the single aromatic ring. 6 The absorption band of the * azoaromatic transition becomes broader in the films, with two additional shoulders at 340 and 380 nm, related respectively to the formation of H-aggregates

layer structure 17 1990 1 148 103 10.1016/0301-0104(90)89011-E Broo Anders Larsson Sven Chemical Physics Chemical Phys 03010104 Electron transfer due to through-bond interactions. Study of aliphatic chains 18 1989 1-2 179 397 10.1016/0040-6090(89)90212-5 Alfimov M.V Lednev I.K Styrkas D.A Thin Solid Films This Solid Films 00406090 Spectral and luminescent properties of Langmuir-Blodgett films of stilbazole salt: Formation of H aggregates 19 1989 173 531 10.1557/PROC-173-531 Metzger Robert M. Panetta Charles A. MRS Proceedings Mater Res Soc Proc 19464274 Langmuir