J/H aggregates

Figure 16. Reversible change of monolayer spectra among J-, H-aggregates and monomeric species of squarylium with four butyl groups by compression.

BORDEN, J.H., Aggregation pheromones. Comprehensive Insect Physiol, Biochem., Pharmacol., 1985, 257-285. 

Borden, J. H. Aggregation pheromones, pp. 257-285, In Comprehensive Insect Physiology, Biochemistry and Pharmacology Vol. 9, Kerkut, G. A. and L. I. Gilbert (eds.). Pergamon, Oxford, United Kingdom, 1985. 

Yeskie M A and Harwell J H 1988 On the structure of aggregates of adsorbed surfactants The surface charge... 

There are two main kinds of dye aggregates, characterized by their typical spectral properties J-aggregates and H-aggregates. The absorption band maximum (f-band) of the J-aggregates is shifted bathochromicaHy with respect to that of an isolated molecule (M-band) the absorption maximum of the H-aggregates is shifted hypsochromicaHy (H-band). The dyes can also form dimers with a shorter absorption wavelength (D-band). 

Ford-Hutchinson, A.W., Bray, M.A., Doig, M.V., Shipley, M.E., Smith, M.J.H. (1980). Leukotreine B, a potent chemokinetic and aggregating substance released from polymorphonuclear leukoctyes. Nature, 286, 264—265. 

Youk J.H., Park M.K., Locklin J., Advincula R., Yang J., and Mays J. Preparation of aggregation stable gold nanoparticles using star-block copolymers, Langmuir, 18, 2455, 2002. 

Humphrey, S.M., Mack, H.-G., Redshaw, C., Elsegood, M.R.J., Yormg, K.J.H., Mayerand, H.A. and Kaskad, W.C. (2005) Variable solid state aggregations in a series of (isocyanide)gold(I) halides with the novel trimethylamine-isocyanoborane adduct. Dalton Transactions, (3),... 

Parkash, J., J.H. Robblee, J. Agnew, E. Gibbs, P. Collings, R.F. Pasternack, and J.C de Paula. 1998. Depolarized resonance light scattering by porphyrin and chlorophyll a aggregates. Biophys. J. 74 2089-2099. 

Regardless of the initial concentration of zeaxanthin, when ethanol is used as the primary solvent, a water content larger than 50% always promotes the formation of H-aggregates (Ruban et al. 1993, Billsten et al. 2005). Thus, it seems that the proper choice of solvent may shift the concentration window in which the J-aggregates are formed. 

In some cases, a transition between J- and H-aggregates has also been observed. Mori et al. (1996) showed that astaxanthin H-aggregates transform into J-aggregates in a few hours. These authors studied the transformation in the 2°C-32°C temperature range and concluded that assemblies corresponding to H- and J-aggregates are separated by an energy barrier that allows the H to J... 

FIGURE 8.7 Transient absorption spectra recorded 3ps following excitation for zeaxanthin (a) and ACOA (b). The spectra were measured with excitation at 400 nm (H-aggregates), 485 nm (monomers), and 525 nm (J-aggregates). 

FIGURE 8.8 Kinetics at the maxima of the S1-SN bands of aggregated and monomeric forms of zeaxanthin (a) and ACOA (b). Probing wavelengths were 555 (zeaxanthin monomer), 560 (zeaxanthin H-aggregates), 605 (zeaxanthin J-aggregates), 520 (ACOA monomer), and 530 nm (ACOA H-aggregates). 

Much less is known about excited-state dynamics of carotenoid J-aggregates, as only zeaxanthin J-aggregates have been studied to date. Only two decay components of -5 and 30ps were needed to fit the kinetics recorded at the maximum of the Sj-S band, Figure 8.8. Since no annihilation studies were carried out, the origin of these components is not known. It is likely that the 5ps lifetime is due to annihilation whereas the 30 ps component corresponds to the. S, lifetime, which is even longer than that of the H-aggregates. 

Spano, F. C. 2009. Analysis of the UV/Vis and CD spectral line shapes of carotenoid assemblies Spectral signatures of chiral H-aggregates. J. Am. Soc. 131 4267-4278. 

---