Design and Characterization of Molecular Nonlinear Optical Switches

Abstract

Nanoscale structures, including molecules, supramolecules, polymers, functionalized surfaces, and crystalline/amorphous solids, can commute between two or more forms, displaying contrasts in their nonlinear optical (NLO) properties. Because of this property, they have high potential for applications in data storage, signal processing, and sensing. As potential candidates for integration into responsive materials, scientists have been intensely studying organic and organometallic molecules with switchable first hyperpolarizability over the past two decades. As a result of this, researchers have been able to synthesize and characterize several families of molecular NLO switches that differ by the stimulus used to trigger the commutation. These stimuli can include light irradiation, pH variation, redox reaction, and ion recognition, among others. The design of multistate (including several switchable units) and multifunctional (triggered with different stimuli) systems has also motivated a large amount of work, aiming at the improvement of the storage capacity of optical memories or the diversification of the addressability of the devices. In complement to the synthesis of the compounds and the characterization of their NLO responses by means of hyper-Rayleigh scattering, quantum chemical calculations play a key role in the design of molecular switches with high first hyperpolarizability contrasts. Through the latter, we can gain a fundamental understanding of the various factors governing the efficiency of the switches. These are not easily accessible experimentally, and include donor/acceptor contributions, frequency dispersion, and solvent effects. In this Account, we illustrate the similarities of the experimental and theoretical tools to design and characterize highly efficient NLO switches but also the difficulties in comparing them. After providing a critical overview of the different theoretical approaches used for evaluating the first hyperpolarizabilities, we report two case studies in which theoretical simulations have provided guidelines to design NLO switches with improved efficiencies. The first example presents the joint theoretical/experimental characterization of a new family of multi-addressable NLO switches based on benzazolo-oxazolidine derivatives. The second focuses on the photoinduced commutation in merocyanine-spiropyran systems, where the significant NLO contrast could be exploited for metal cation identification in a new generation of multiusage sensing devices. Finally, we illustrate the impact of environment on the NLO switching properties, with examples based on the keto-enol equilibrium in anil derivatives. Through these representative examples, we demonstrate that the rational design of molecular NLO switches, which combines experimental and theoretical approaches, has reached maturity. Future challenges consist in extending the investigated objects to supramolecular architectures involving several NLO-responsive units, in order to exploit their cooperative effects for enhancing the NL...

Approaching exact hyperpolarizabilities via sum-over-states Monte Carlo configuration interaction

“…4,5 Such switches have also been put forward as tools to detect the presence of certain molecules (see, for example, Ref. 6).…”

Light induced nonlinear optical switch in boronated chromophores: A theoretical search towards high contrast switches in the azobenzene series

“…While most of the attempts to get convincing switches have focused on a reversible redox behavior of the donor substituent (e.g. Ru II /Ru III ), [7] using the light induced isomerization of the bridge has been reported as an alternative strategy, for instance in the case of diarylethene chromophores, [8,9] oxazolidine and spiropyrane systems, [10] or in azobenzene derivatives (AB, Scheme 1), such as the commercially available Disperse Red One dye (DR1, Scheme 1). [11] Indeed, the light induced E / Z isomerization of azobenzene derivatives is well documented and reviewed.…”

The inner-induced effects of YCN in C76 on the structures and nonlinear optical properties

“…Nonlinear optical materials are of great importance for potential applications in optical computation, optical communication, second harmonic generation, and optical signal processing [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. So far, nonlinear optical materials are mainly divided into two conventional classes: inorganic and organic materials [13,[17][18][19].…”