Nonlinear Optical Properties of X(C₆H₅)₄ (X = B^–, C, N⁺, P⁺): A New Class of Molecules with a Negative Third-Order Polarizability

Organic π-conjugated materials have been widely used for a variety of nonlinear optical (NLO) applications. Molecules with negative real components Re­(γ) of the third-order polarizability, which leads to nonlinear refraction in macroscopic systems, have important benefits for several NLO applications. However, few organic systems studied to date have negative Re­(γ) in the long wavelength limit, and all inorganic materials show positive nonlinear refraction in this limit. Here, we introduce a new class of molecules of the form X­(C₆H₅)₄, where X = B^–, C, N⁺, and P⁺, that have negative Re­(γ). The molecular mechanism for the NLO properties in these systems is very different from those in typical linear conjugated systems: These systems have a band of excited states involving single-electron excitations within the π-system, several of which have significant coupling to the ground state. Thus, Re­(γ) cannot be understood in terms of a simplified essential-state model and must be analyzed in the context of the full sum-over-states expression. Although Re­(γ) is significantly smaller than that of other commonly studied NLO chromophores, the introduction of a new molecular architecture offering the potential for a negative Re­(γ) introduces new avenues of molecular design for NLO applications

Photodriven Oxygen Removal via Chromophore-Mediated Singlet Oxygen Sensitization and Chemical Capture

We report a general, photochemical method for the rapid deoxygenation of organic solvents and aqueous solutions via visible light excitation of transition metal chromophores (TMCs) in the presence of singlet oxygen scavenging substrates. Either 2,5-dimethylfuran or an amino acid (histidine or tryptophan methyl ester) was used as the substrate in conjunction with an iridium or ruthenium TMC in toluene, acetonitrile, or water. This behavior is described for solutions with chromophore concentrations that are pertinent for both luminescence and transient absorption spectroscopies. These results consistently produce TMC lifetimes comparable to those measured using traditional inert gas sparging and freeze–pump–thaw techniques. This method has the added benefits of providing long-term stability (days to months); economical preparation due to use of inexpensive, commercially available oxygen scrubbing substrates; and negligible size and weight footprints compared to traditional methods. Furthermore, attainment of dissolved [O₂] < 50 μM makes this method relevant to any solution application requiring low dissolved oxygen concentration in solution, provided that the oxygenated substrate does not interfere with the intended chemical process

Supplement 1: Temporal, spectral, and polarization dependence of the nonlinear optical response of carbon disulfide

Originally published in Optica on 20 December 2014 (optica-1-6-436