Oxazines: A New Class of Second-Order Nonlinear Optical Switches

Abstract

A combined experimental-theoretical investigation has revealed that oxazine-based compounds are multiaddressable, multistate, and multifunctional molecular switches exhibiting contrasts of both linear and second-order nonlinear optical properties. The switching properties are particularly large when the substituent is a donor group. In this study, the cleavage of the C-O bond at the junction of the indole and oxazine cycles (of the closed a forms) is acido-triggered, leading to an open form (b(+)) characterized by larger first hyperpolarizabilities (βHRS) and smaller excitation energies than in the closed form. These results are confirmed and interpreted utilizing ab initio calculations that have been carried out on a broad set of compounds to unravel the role of the substituent. With respect to acceptor groups, oxazines bearing donor groups are characterized not only by larger βHRS and βHRS contrast ratios but also by smaller excitation energies, larger opening-induced charge transfer, and reduction of the bond length alternation, as well as smaller Gibbs energies of the opening reaction. Compared to protonated open forms (b(+)), calculations on the zwitterionic open forms (b) have pointed out similarities in the long-wavelength UV/vis absorption spectra, whereas their βHRS values might differ strongly as a function of the substituent. Indeed, the open forms present two NLOphores, the indoleninium-substituent entity and the nitrophenol (present in the protonated open form, b(+)) or nitrophenolate (present in the zwitterionic open form, b) moiety. Then, nitrophenolate displays a larger first hyperpolarizability than nitrophenol and the β tensor of the two entities might reinforce or cancel each other.

Second-order nonlinear optical switching with a record-high contrast for a photochromic and thermochromic bistable crystal

“…In the past few years, materials displaying switchable NLO properties have drawn much attention 2–10. On one side, they provide an in situ , reversible, and controllable method for regulating NLO properties.…”

A Multi‐Stimuli‐Responsive Oxazine Molecular Switch: A Strategy for the Design of Electrochromic Materials

“…[40,41] More importantly, the colors of pH-sensitive molecular switches exhibit wide variety,h ighp urity,a nd ideal molar absorption coefficients. [42][43][44] An "electro-acid/base" was used by our group to extend the application of pH-sensitive molecular switches into ECM. [42][43][44] An "electro-acid/base" was used by our group to extend the application of pH-sensitive molecular switches into ECM.…”

“…However,t he application of pHsensitivem olecular switches in ECM is hindered by the lack of an electrical response ability. [42][43][44] An "electro-acid/base" was used by our group to extend the application of pH-sensitive molecular switches into ECM. [45][46][47] Electro-acids/bases (e.g., pphenylenediamine and benzoquinone) are at ype of molecule in which the oxidative or reductives tate is able to captureo r lose ap roton.…”

Structural diradical character

“…It would be particularly useful if the NLO properties of molecules or molecular materials could be switched by external stimuli. There has been considerable experimental and theoretical work on switchable organic and organometallic NLO‐active molecules, showing that a variety of stimuli such as pH, temperature, redox reactions, and light can be used for this purpose.…”