What's H aggregate

Answer 1

Molecular aggregates in which the individual molecules (monomers) are arranged in a regular fashion are of particular interest because of their unique electronic and spectroscopic properties, for example J-aggregates and H-aggregates. The J-aggregate is a one-dimensional molecular arrangement in which the transition moments of individual monomers are aligned parallel to the line joining their centers (end-to-end arrangement). The H-aggregate is also a one-dimensional array of molecules in which the transition moments of individual monomers are aligned parallel to each other but perpendicular to the line joining their centers (face-to-face arrangement). The most characteristic feature of J-aggregate is that they exhibit a narrow peak (J-band) red-shifted in the absorption spectrum with respect to the monomer absorption. The absorption spectrum of the H-aggregate consists of a blue-shifted band (generally is not as narrow as the J-band) with respect to the monomer absorption. The energy shift of the absorption bands of the aggregates has been explained by exciton theory.