Design Principles for Two-Dimensional Molecular Aggregates Using Kasha’s Model: Tunable Photophysics in Near and Short-Wave Infrared

Abstract

Technologies which utilize near-infrared (NIR) (700–1000 nm) and short-wave infrared (1000–2000 nm) electromagnetic radiation have applications in deep-tissue imaging, telecommunications, and satellite telemetry due to low scattering and decreased background signal in this spectral region. It is therefore necessary to develop materials that absorb light efficiently beyond 1000 nm. Transition dipole moment coupling (e.g., J-aggregation) allows for red-shifted excitonic states and provides a pathway to highly absorptive electronic states in the infrared. We present aggregates of two cyanine dyes whose absorption peaks red-shift dramatically upon aggregation in water from ∼800 to 1000 nm and 1050 nm, respectively, with sheet-like morphologies and high molar absorptivities (e ≈ 105 M–1 cm–1). We use Frenkel exciton theory to extend Kasha’s model for J- and H-aggregations and describe the excitonic states of two-dimensional aggregates whose slip is controlled by steric hindrance in the assembled structure. A c...