Syntheses and properties of two-dimensional, dicationic nonlinear optical chromophores based on pyrazinyl cores

Electrochemically-Switched 2nd Order Non-Linear Optical Response in an Arylimido-Polyoxometalate with High Contrast and Cyclability

Electrochemically switched 2^nd order non-linear optical responses have been demonstrated for the first time in polyoxometalates (POMs), with an arylimido-derivative showing a leading combination of high on/off contrast (94 %), high visible transparency, and cyclability. Spectro-electrochemical and TD-DFT studies indicate that the switch-off results from weakened charge transfer (CT) character of the electronic transitions in the reduced state. This represents the first study of an imido-POM reduced state, and demonstrates the potential of POM hybrids as electrochemically activated molecular switches.

Second-order nonlinear polarizability of "Push-Pull" chromophores. A decade of progress in donor-π-acceptor materials

Fine tuning and switching of nonlinear optical response of ferrocene chromophores has been an area of considerable significance as evidenced by a large number of reports in the current literature. In this personal account, we present linear/nonlinear behavior and structure-activity relationships of several classes of donor-π-acceptor designs using organometallic and organic materials, developed by our research group during the last decade. The results especially the electronic absorption spectral and the hyper-Rayleigh scattering have been supported by theoretical calculations. Exploiting the redox behavior of ferrocene donor, we have demonstrated switching of quadratic nonlinear optical responses with reversible redox chemistry, which is a useful attribute of nonlinear optical materials. Based on the ease in synthesis, structure diversification and structure-based large and switchable second-order optical nonlinearity, these materials are potential candidates for electro-optic applications.

Mono- and Di-Quaternized 4,4'-Bipyridine Derivatives as Key Building Blocks for Medium- and Environment-Responsive Compounds and Materials

Mono- and di-quaternized 4,4'-bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4'-bipyridine-based derivatives are exploited: their redox activity and their electrochromic aptitude. Contemporary materials and compounds encompassing these skeletons as building blocks are often characterized as multifunctional, as their presence often gives rise to interesting phenomena, e.g., various types of chromism. This research trend is acknowledged, and, in this review article, recent examples of multifunctional chromic materials/compounds of this class are presented. Emphasis is placed on solvent-/medium- and environment-responsive 4,4'-bipyridine derivatives. Two important classes of 4,4'-bipyridine-based products with solvatochromic and/or environment-responsive character are reviewed: viologens (i.e., N,N'-disubstituted derivatives) and monoquats (i.e., monosubstituted 4,4'-bipyridine derivatives). The multifunctional nature of these derivatives is analyzed and structure-property relations are discussed in connection to the role of these derivatives in various novel applications.

Large-sized benzo[e]indolium salt single crystals with high optical nonlinearity

Two new benzo[e]indolium salts with highly efficient nonlinear optical performance and excellent crystal characteristics were synthesized.

Donor–acceptor organo-imido polyoxometalates: high transparency, high activity redox-active NLO chromophores

Organoimido polyoxometalates are a powerful new class of acceptor for non-linear optics. As a basis for donor–acceptor systems, they offer an excellent transparency/non-linearity trade-off and break through empirical performance limits for comparable organic materials.

Influence of spiral framework on nonlinear optical materials

A series of spiral donor-π-acceptor frameworks (i.e. 2-2, 3-3, 4-4, and 5-5) based on 4-nitrophenyldiphenylamine with π-conjugated linear acenes (naphthalenes, anthracenes, tetracenes, and pentacenes) serving as the electron donor and nitro (NO2 ) groups serving as the electron acceptor were designed to investigate the relationships between the nonlinear optical (NLO) responses and the spirality in the frameworks. A parameter denoted as D was defined to describe the extent of the spiral framework. The D value reached its maximum if the number of NO2 groups was equal to the number of fused benzene rings contained in the linear acene. A longer 4-nitrophenyldiphenylamine chain led to a larger D value and, further, to a larger first hyperpolarizability. Different from traditional NLO materials with charge transfer occurring in the one-dimensional direction, charge transfer in 2-2, 3-3, 4-4, and 5-5 occur in three-dimensional directions due to the attractive spiral frameworks, and this is of great importance in the design of NLO materials. The origin of such an enhancement in the NLO properties of these spiral frameworks was explained with the aid of molecular orbital analysis.

THEORETICAL STUDY ON THE SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF C,B-SUBSTITUTED CARBORANE CONJUGATED DERIVATIVES

To systemically investigate structure–property relationship and design excellent nonlinear optical (NLO) material, the second-order NLO properties of a series of C,B -substituted carborane conjugated derivatives have been studied by density functional theory (DFT). The static first hyperpolarizabilities (βtot) were calculated at the M05-2X/6-31+G* level of theory. The results show that the βtot values gradually increase with the increasing of the conjugation length, especially the introduction of ferrocene. It is found that 1,3-benzo-o-carborane-ferrocene (2h) has the largest first hyperpolarizability (55.968 × 10-30 esu), which is 150 times larger than that of benzocarborane (1a). This means that the static first hyperpolarizabilities of the studied compounds can be substantially increased by structural modification. A basis for understanding the origin of these large NLO responses is proposed based on consideration of the frontier molecular orbitals (FMOs), orbital energy, transition energy of the studied compounds, and the two-state mode. The lower transition energy and larger oscillator strength play an important role in increasing the first hyperpolarizability value. This study may evoke possible ways to design preferable NLO materials.