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We report a significant Stokes shift enhancement in near-infrared fluorescing cyanines as a result of C4′-substitution with cyclic or acyclic amines. Based on a combined experimental and density functional study, a simple strategy for optimizing the Stokes shift is proposed. By tuning the relative energies of cyanine-like and bis-dipolar conformers, differing in the rotational angle of the amine substituent, it is possible to develop molecules that undergo conformational change upon excitation, resulting in a predictable Stokes shift. 

Abstract Visibly transparent luminescent solar concentrators (TLSC) have the potential to turn existing infrastructures into net-zero-energy buildings. However, the reabsorption loss currently limits the device performance and scalability. This loss is typically defined by the Stokes shift between the absorption and emission spectra of luminophores. In this work, the Stokes shifts (SS) of near-infrared selective-harvesting cyanines are altered by substitution of the central methine carbon with dialkylamines. We demonstrate varyingSSwith values over 80 nm and ideal infrared-visible absorption cutoffs. The corresponding TLSC with such modification shows a power conversion efficiency (PCE) of 0.4% for a >25 cm²device area with excellent visible transparency >80% and up to 0.6% PCE over smaller areas. However, experiments and simulations show that it is not the Stokes shift that is critical, but the total degree of overlap that depends on the shape of the absorption tails. We show with a series ofSS-modulated cyanine dyes that theSSis not necessarily correlated to improvements in performance or scalability. Accordingly, we define a new parameter, the overlap integral, to sensitively correlate reabsorption losses in any LSC. In deriving this parameter, new approaches to improve the scalability and performance are discussed to fully optimize TLSC designs to enhance commercialization efforts.