Near IR Nonlinear Absorbing Chromophores with Optical Limiting Properties at Telecommunication Wavelengths

Dipolar and symmetrical heptamethine dyes featuring strong linear absorption in the near-infrared spectral range (700−900 nm) were prepared at a gram scale. X-ray crystallographic structure of the dipolar chromophore is described revealing the remarkable planarity of the polyenic chain due to the central ring of the molecule. These chromophores present promising nonlinear absorption properties at telecommunication wavelengths (1400−1600 nm): (i) significant two-photon cross-sections were measured using the femtosecond Z-scan method, and (ii) their exceptional solubility allows us to carry out an optical-limiting experiment at 1500 nm in the nanosecond regime. In this regime, experimental data were interpreted on the basis of two-photon absorption (2PA) and 2PA-induced excited-state absorption (ESA). Finally, these systems, which present a lot of relevant properties (significant nonlinear absorption properties, two-step gram scale synthesis, high solubility, good thermal stability, and several sites of functionalization), open the way to numerous practical applications in biology, solid-state optical limiting, and signal processing.