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The helical structure is a classical framework to design high-performance organic electro-optical materials. In this work, the structure-property's relationships of helical tetraspirobenzene (1) and its oxidation (12+) and reduction (12–) products are explored. The results show that the redox brings some distinctive changes in their geometric structure and electronic property, which regulate the first hyperpolarisability (βtot). Among these structures, the 12– has the largest βtot value of 4.2 × 104, which is greatly larger than 2.0 × 102 a.u. of. 12+. Therefore, the reduction effect is more obvious than the oxidation effect. Furthermore, the UV-Vis absorption spectrum also proves this phenomenon: the oxidation product has a new red-shifted absorption peak (571 nm) and the reduction product has two new red-shifted absorption peaks (577 and 797 nm). We hope the present work can provide theoretical guidance for the search for high-performance nonlinear optical materials by using the redox effect. [ABSTRACT FROM AUTHOR]

This study spotlights the fundamental insights about the structure and static first hyperpolarizability ( β) of a series of 2,4-dinitrophenol derivatives (1-5), which are designed by novel bridging core modifications. The central bridging core modifications show noteworthy effects to modulate the optical and nonlinear optical properties in these derivatives. The derivative systems show significantly large amplitudes of first hyperpolarizability as compared to parent system 1, which are 4, 46, 66, and 90% larger for systems 2, 3, 4, and 5, respectively, at Moller-Plesset (MP2)/6-31G* level of theory. The static first hyperpolarizability and frequency dependent coupled-perturbed Kohn-Sham first hyperpolarizability are calculated by means of MP2 and density functional theory methods and compared with respective experimental values wherever possible. Using two-level model with full-set of parameters dependence of transition energy (Δ Ε), transition dipole moment ( μ0) as well as change in dipole moment from ground to excited state (Δ μ), the origin of increase in β amplitudes is traced from the change in dipole moment from ground to excited state. The causes of change in dipole moments are further discovered through sum of Mulliken atomic charges and intermolecular charge transfer spotted in frontier molecular orbitals analysis. Additionally, analysis of conformational isomers and UV-Visible spectra has been also performed for all designed derivatives. Thus, our present investigation provides novel and explanatory insights on the chemical nature and origin of intrinsic nonlinear optical (NLO) properties of 2,4-dinitrophenol derivatives. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Carbon-boron-nitride heteronanotubes have attracted much interest owing to their adjustable properties and wide applications in many fields. In this work, the structures and first hyperpolarizabilities ( β0) of a series of HA- n and isoelectronic PA- n heteronanotubes are investigated, in which HA- n is composed of a helical C segment and BN segment, and PA- n is composed of an arc C segment and BN segment. Interestingly, the helix C segment in HA-9 leads to a fascinating long-range charge-transfer character. As a result, the β0 value of HA-9 is 1.80×104 a.u., which is much larger than that of PA-9 (4.99×103 a.u.). Significantly, the β0 value of the C segment in HA-9 is 1.72×104 a.u., whereas that of the BN segment in HA-9 is much smaller (7.48×102 a.u.). In this context, the larger β0 value of HA-9 is essentially induced by the helix topological effect of the C segment. It is our expectation that this new knowledge about heteronanotubes might provide more ideas for further exploration of sp2-hybridized carbon segments with special topologies. [ABSTRACT FROM AUTHOR]

In our previous work, new alkalides Li+(calix [4]pyrrole)M− with cup‐like complexant have been reported for the large static first hyperpolarizabilities (β0) (Chen et al., J Am Chem Soc 2006, 128, 1072). In this work, new inorganic alkalides are found by using a more flexible complexant, methylamine (NH2CH3)4. The structures with all real frequencies and β0 values of the inorganic alkalides Li+(cage [4]methylamine)M− (M = Li, Na, and K) are obtained at MP2 level. The result shows that these inorganic alkalides have more considerable β0 values to be 18,825 (M = Li) < 27,942 (M = Na) < 81,094 au (M = K), which are more than two times larger than those (10,969 ∼ 35,934 au) of the reported alkalides Li+(calix [4]pyrrole)M−. To understand this structure–property relationship, two cup‐like Li+(NH2CH3)4M− (M = Li, Na, and K) models are designed to compare their β0 values. By comparing the β0 values among the cup‐like alkalides Li+(calix [4]pyrrole)M−, Li+(NH2CH3)4M−, and cage‐like alkalides Li+(cage [4]methylamine)M− (M = Li, Na, and K), the complexant shape effect of alkalides has been revealed. It is found that the complexant shape is an important factor in large β0 values. Moreover, the monotonic dependences of β0 on the Li–M distance and the NBO charges of cation (Li+) and anions (M−) in inorganic alkalides Li+(cage [4]methylamine)M− have been shown. In this work, the frequency dependent first (hyper)polarizabilities are also determined. It is found that both the frequency dispersion and the effects of the electron correlation are strong. Moreover, the dependence of both the static and frequency dependent β on the atomic number of alkali metal anions is similar. This work provides a new way to understand the nature of high‐performance nonlinear optical (NLO) materials, and it is helpful to design new NLO materials. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011. [ABSTRACT FROM AUTHOR]

A family of hydrazone-based photochromic derivatives consisting a hydrazone switching and phenyl groups with R 1 and R 2 (R = H, -NO 2 and -NMe 2) can be induced by light to form two isomers (Z-type and E-type). In this paper, we discussed detailedly the impacts of structural change on UV–Vis absorption spectra, electronic transition properties and the first hyperpolarizability (β tot) by using density functional theory (DFT) methods. The calculation results showed that second-order NLO responses of Z-type complexes are stronger than that of corresponding E-type complexes due to the red-shift of absorption spectra, the smaller electronic transition energy (Δ E ge) and the narrower energy band gap (E gap) of frontier molecular orbital. Furthermore, the push-pull complexes 4 may be potential NLO materials due to the larger β tot values, for example, the β tot values of 4Z and 4E are 1.6 × 104 a.u. and 9.3 × 103 a.u., respectively. It is that the donor (D) and acceptor (A) groups are dominated by the interaction of D and A group via intramolecular charge transition (CT). We hope that this research will introduce a new relation between the structure and the photochromic nonlinear optical activity. The impacts of configuration change that was induced by UV-light on NLO response were studied by DFT. We found that the NLO properties of Z-type compounds are better than that of E-type, due to the lower HOMO-LUMO energy gap and electron transition energy. In addition, push-pull systems 4 show high NLO response that is expected to be a new nonlinear optical material. Unlabelled Image • The work revealed the relation of structure and NLO property for hydrazone complexes. • The NLO response of Z-type complexes are larger than that of E-type complexes. • The electron transition is an important factor to impact NLO properties. • Push-pull complex shows good NLO response due to the more obvious intramolecular CT. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new hybrid model (BNC-n) are designed by the increasing vertical carbon-segment doping into the BN nanosheet. • The first hyperpolaizability of isoelectronic are increased with the increase of the doping carbon-segment. • With the increase of the vertical carbon-segment, the polarizability of isoelectronic gradually increase. Due to wide applications in optoelectronic field, carbon-boron-nitride materials have attracted considerable interest from scientists. In the present work, the structures and first hyperpolarizility (β tot) of three closed shell isoelectronic structures BNC-n (n = 1–3) were investigated, in which BNC-n are designed by the increasing vertical carbon-segment doping into the BN nanosheet. Results show the β tot value of isoelectronic are increased with the increase of the doping carbon-segment. Among these isoelectronic structures, the β tot value (2.80 × 104 au) of BNC-3 is larger (19 times) than the 1.51 × 103 au of BNC-1. Correspondingly, the BNC-3 has the smallest transition energy (1.455 eV), which is obviously smaller than 3.884 eV of BNC-1. We hope the present work is beneficial for scientists to understand and design high performance nonlinear optical materials on carbon-boron-nitride hetero-materials. [ABSTRACT FROM AUTHOR]

It is well known that settling transparency-efficiency tradeoff is important to design nonlinear optical (NLO) materials. In this work, we constructed one-dimensional polymeric cyanoacetylene (N C C C H) n by hydrogen-bond-directed-linking to understand this tradeoff from molecular level. Results show that the first hyperpolarizability of (N C C C H) n ( n = 2–8) gradually increased with the increase of n , and what is more important is that the red-shifts, associated with the increase of n , were very little. It is proposed that these polymeric structures possess double-degenerated charge transitions, which contribute to the hyperpolarizability in an additive fashion, and that the coupled oscillators are gradually improved, which lead to the increase of the first hyperpolarizability. Therefore, we propose the hydrogen-bond-directed-linking idea is helpful to develop the potential high-performance NLO materials. [ABSTRACT FROM AUTHOR]

A fascinating crown-porphyrin (Cr-Pr) complexes are investigated with doping potassium (K atom) on the crown ether face and introducing zinc (Zn atom) on the porphyrin face. Significantly, the crown ether ring is doped with K atom, the second-order nonlinear optical properties of the complexes are enhanced and regulated, offering promising prospects for advanced applications in the field of optics. [Display omitted] • A fascinating crown-porphyrin complexes were designed and investigated. • The ESP maps and NPA charges show that the charge distribution is regulated obviously. • The incorporation of K atom enhances effectively the β tot value. • The change in β tot values can be well explained by the two-level model. Crown ethers have inspired the rapid growth of research interest in the design and synthesis of functional materials due to their exceptional affinity for metal. In this work, a fascinating crown-porphyrin (Cr-Pr) complexes were studied with doping alkali metal (potassium, K atom) on the crown ether face and introducing transition metal (zinc, Zn atom) on the porphyrin face. The research reveals that the Cr-Pr complex with doped K and Zn atoms results in significant variations in nonlinear optical (NLO) properties. Interestingly, the crown ether ring with the K atom in the K@Cr-Pr complex leads to a remarkable first hyperpolarizability (β tot). On the contrary, when introducing the Zn atom in porphyrins, the Cr-Pr@Zn complex exhibits no significant change in NLO response. Further, the combination of the K and Zn atoms in crown-porphyrin complex (K@Cr-Pr@Zn) can result in significant enhancement of their NLO characteristics, which is much greater than that of the K@Cr-Pr and the Cr-Pr@Zn complexes. The natural population analysis (NPA) and the molecular electrostatic potential maps (ESP) show that the doping of the K atom regulates effectively charge distribution in the complexes. Moreover, the great β tot value can be further illustrated by their low transition energies and an obvious charge transfer (CT) transition in the main excited states. Therefore, the current work achieves that the NLO properties of crown ether derivatives can be regulated by doping alkali metals in the crown ether ring and provides a theoretical guide for developing high-performance NLO devices. [ABSTRACT FROM AUTHOR]

Recently, the structure-property relationships of an attractive isomeric radical 1 ( Phys. Chem. Chem. Phys. , 2016, 18, 29041–29044) with famous phenalenyl ( PLY ) was investigated. Can PLY and 1 form stable π-dimers? The single point energy scan result shows that the staggered π-dimer ( 2 ) has the lowest energy. In order to explore intermolecular charge-transfer and nonlinear optical property, two π-dimers ( 2a and 2b by boron and nitrogen atoms substituting the central carbon atoms of 2 ) are designed. 2 has smaller intermolecular charge-transfer (0.020) and the first hyperpolarizability ( β tot , 3.18 × 10 2 au). However, boron and nitrogen substitution effect can greatly enhance intermolecular charge-transfer (0.215 for 2a and 0.181 for 2b ) and the β tot values (6.32 × 10 3 for 2a and 6.80 × 10 3 for 2b ). Interestingly, the β tot values of 2a and 2b are close to each other, but their β z components and the NBO charge analysis show that 2a and 2b have opposite direction of charge transfer, which can be well explained by the difference of the dipole moment component (Δ μ z ) between the ground and the excited states. Further, the first hyperpolarizability density study clearly substantiates the difference in their β zzz values: negative contribution for 2a is much larger than positive contribution, while the first hyperpolarizability density for 2b shows much larger positive contribution. Thus, the primary component of β zzz is negative value for 2a and β zzz is positive value for 2b . Combining with the frontier molecular orbital (FMO) and the electron density difference map (EDDM), intermolecular charge-transfer transition from B substituted fragment to N substituted fragment for 2a and 2b is concluded. The significant structure-property relationships in present π-dimers are beneficial for further theoretical and experimental investigations of high-performance nonlinear optical materials. [ABSTRACT FROM AUTHOR]