Switchable Nonlinear Optical Properties of η⁵-Monocyclopentadienylmetal Complexes: A DFT Approach

Abstract

Density functional theory (DFT) calculations have been carried out to investigate the switching of the second-order nonlinear optical (NLO) properties of η(5)-monocyclopentadienyliron(II) and ruthenium(II) model complexes presenting 5-(3-(thiophen-2-yl)benzo[c]thiophen-1-yl)thiophene-2-carbonitrile as a ligand. The switching properties were induced by redox means. Both oxidation and reduction stimulus have been considered, and calculations have been performed both for the complexes and for the free benzo[c]thiophene derivative ligand in order to elucidate the role played by the organometallic fragment on the second-order NLO properties of these complexes. B3LYP, CAM-B3LYP, and M06 functionals were used for our calculations. The results show some important structural changes upon oxidation/reduction that are accompanied by significant differences on the corresponding second-order NLO properties. TD-DFT calculations show that these differences on the second-order NLO response upon oxidation/reduction are due to a change in the charge transfer pattern, in which the organometallic iron and ruthenium moieties play an important role. The calculated static hyperpolarizabilities were found to be strongly functional dependent. CAM-B3LYP, however, seems to predict more reliable structural and optical data as well as hyperpolarizabilities when compared to experimental data. The use of this functional predicts that the studied complexes can be viewed as acting as redox second-order NLO switches, in particular using oxidation stimulus. The β(tot) value of one-electron oxidized species is at least ~8.3 times (for Ru complex) and ~5.5 times (for Fe complex) as large as that of its nonoxidized counterparts.

Redox control of ferrocene-based complexes with systematically extended π-conjugated connectors: switchable and tailorable second order nonlinear optics

“…[1][2][3][4][5] Up to now, many strategies have been proposed to enhance the NLO responses of materials, including increasing the strength of the donor/acceptor groups, expanding the length of the p-conjugated bridge, twisting p-electron systems, constructing octupolar molecules, doping the alkali metals into the organic compounds, etc. [6][7][8][9][10][11][12][13] The studies of various NLO chromophores and their properties are the important basis for designing and synthesizing new NLO materials.…”

“…Although fundamental research studies of NLO properties have been mostly devoted to the preparation of chromophores with large optical nonlinearities, the use of these properties in view of the molecular switches has attracted considerable interest. 10,11 Molecular switches are molecules that are reversibly switchable between at least two forms that have different ''readable'' properties and are stable in these forms for at least as long as the measurement time for the readout. 11 That is to say, to achieve effective NLO switches, the molecule must be stable in two states ('ON' and 'OFF' states) and exhibit a large difference in NLO responses.…”

“…10,11 Molecular switches are molecules that are reversibly switchable between at least two forms that have different ''readable'' properties and are stable in these forms for at least as long as the measurement time for the readout. 11 That is to say, to achieve effective NLO switches, the molecule must be stable in two states ('ON' and 'OFF' states) and exhibit a large difference in NLO responses. 14 The different NLO properties can be readily affected by applying various external and common stimuli, such as photoexcitation, 15 temperature, 16 pH 17,18 and redox reaction.…”

Ferrocene/fullerene hybrids showing large second-order nonlinear optical activities: impact of the cage unit size

“…It is both instructive and useful to accumulate experience on the performance of various methods in the evolution of the reliable hyperpolarizability. [79][80][81][82] Several studies have pointed out that the DFT functional with a large fraction of HF (i.e., BHandHLYP) and the DFT long-range functional (i.e., CAMB3LYP, LC-BLYP, and ωB97XD) not only remove the overestimation of hyperpolarizabilities by standard DFT but also provide semiquantitative accuracy with a reasonable compu-tational cost. 54,83 Recently, it is important to remark that longrange corrected functionals, which introduce a growing fraction of the exact exchange when the distances of these longrange corrected hybrid methods increase, have become promising tools for the evaluation of NLO properties.…”

Carborane tuning on iridium complexes: redox-switchable second-order NLO responses

“…Electrochemical studies also revealed that the two series of Ir complexes exhibit reversible oxidation. It is generally known that oxidation/reduction is one of reported methods employed to switch on the NLO response [35][36][37][38][39][40]. Therefore, the change of oxidation reaction may provide an ideal model for redox switching of the NLO response.…”