With the theoretical design of new functionalized fluorophores for solar energy harvesting, it is possible to obtain systems with desirable properties such as sharp and intense absorption, emissions in the near-infrared region, a high fluorescent quantum yield efficiency, and a transparent window within the visible region. The aim of this work is to study the influence of structural changes on the photochemical properties of squaraine dyes.

Reliable predictions of the properties of their radiative and non-radiative rates, fluorescent lifetime, and quantum yield require the vibrational structure of the studied systems to satisfy the harmonic approximation. We employ a time-dependent density functional formalism (TDDFT) to compute the excited-state properties, spectra, and radiative and non-radiative rates, with the implicitly described solvent effect included throughout the calculations. These systems were modeled using a combination of DFT and TDDFT methods to obtain accurate ground- and excited-state properties relevant to photophysical analyses.

For the investigated indolenine-based squaraine dyes, their trans- and cis-configuration, as well as their substitution into active sites, or structurally sensitive aggregation, can influence their spectral behavior, such as shifting towards the red spectral region or transparency at higher excited states. In addition, a comparison of the theoretically predicted and experimentally measured results is presented.