An Alternative Interpretation for the Spectral Response of Self-Assembled Pseudoisocyanine J-Aggregates in Aqueous Solution

An alternative interpretation for the optical response of pseudoisocyanine J-aggregates is given on the basis of a recently suggested monomeric absorption spectrum exhibiting the seemingly universal spectral fingerprint of cyanines. Temperature-dependence of the generic J-aggregate absorption spectra reported in the literature is quantified by employing simulations obtained in the Frenkel exciton formalism augmented by diagonal energetic disorder and exciton-phonon coupling. It is concluded that the pseudoisocyanine J-aggegates are formed mainly through aggregation of precursor aggregates with absorption around 525 nm upon decrease of temperature and/or increase of dye concentration. This conclusion opposes the common view which attributes the formation of pseudoisocyanine J-aggregates to aggregation of precursors of H-aggregate in nature and to monomers. It is expected that a large number of observations on optical response, and aggregation kinetics, which are still debated on and have been forced to be reconciled in a self-consistent picture through a variety of assumptions, can find reasonable explanations within the alternative viewpoint promoted in this note.