Aggregates of cyanine dyes are currently investigated
as promising
materials for advanced electronic and photonic applications. The spectral
properties of aggregates of cyanine dyes can be tuned by altering
the supramolecular packing, which is affected by the length of the
dye, the presence of alkyl chains, or the nature of the counterions.
In this work, we present a joint experimental and theoretical study
of a family of cyanine dyes forming aggregates of different types
according to the length of the polymethinic chain. Linear and nonlinear
optical spectra of aggregates are rationalized here in terms of an
essential-state model accounting for intermolecular interactions together
with the molecular polarizability and vibronic coupling. A strategy
is implemented to properly account for screening effects, distinguishing
between electrostatic intermolecular interactions relevant to the
ground state (mean-field effect) and the interactions relevant to
the excited states (excitonic effects). To the best of our knowledge,
this is the first attempt to simulate nonlinear spectral properties
of aggregates of symmetric dyes accounting for molecular vibrations.