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Constructing charge transfer (CT) systems and packing arrangement are common and effective methods to control the efficiency of nonlinear optical (NLO) materials. Apart from the traditional through-bond CT (TBCT) systems, through-space CT (TSCT) also leads to distinctive optical and electronic properties. Meanwhile, corresponding theoretical investigations of the aggregation effect are highly desired. In this work, some TSCT and model compounds incorporating acenaphthene as a scaffold and triphenylamine (TPA) as the donor are theoretically performed to systematically reveal the effect of both solvent and solid environments on their static first hyperpolarizabilities (β

It is important to search for efficient nonlinear optical (NLO) materials due to their potential applications in electro-optic devices. Theoretical investigations into the second-order NLO responses of ten novel Ru(II) polypyridyl complexes based on [Ru(phen)

A series of neutral Ir(III) complexes that possess cyclometalated ligands (C^N) and different ancillary ligands, N-heterocyclic carbene (NHC) (R1 = H and R2 = H for complex 1, R1 = NO2 and R2 = H for complex 2, R1 = N(CH3)2 and R2 = H for complex 3, R1 = H and R2 = NO2 for complex 4, and R1 = H and R2 = N(CH3)2 for complex 5) and their ionic complexes 1+/−–5+/− have been investigated using density functional theory. The effects caused by different electron-withdrawing/donating substituents and electronic valence states on their geometries, electronic structures, UV-vis absorption spectra, and second-order nonlinear optical (NLO) properties were explored. The results show that the geometries of these complexes are slightly affected by the variation of the ancillary ligand and the electronic valence state. A significant impact on absorption spectra and second-order NLO properties is observed during the redox process of the neutral complexes. The absorption spectrum has a remarkable red-shift for ionic complexes 1+/−–5+/− compared with their neutral complexes. The obtained βtot values of complexes 1+/−–5+/− range from 7289.2 to 20753.9 a.u., while the value is only 1395.9 a.u. for neutral complex 1. The dramatic enhancement of NLO response is mainly ascribed to the charge redistribution and the variation of transition energy caused by the loss/gain of an electron. Among five neutral complexes, complex 4 presents a high βtot value, 7019.3 a.u. This illustrates that the introduction of a strong electron-withdrawing group in R2 of ancillary ligands promotes the second-order NLO response for this type of cyclometalated Ir(III) complex. This work will be beneficial for designing high performance and excellent switchable NLO materials.

Facile conversion of CO2 into useful multicarbon products is of broad interest in the field of energy storage and controllable carbon emission. However, electrochemical CO2 reduction to ethanol on ...

Through-space charge transfer provides more flexibilities and possibilities to regulate the properties of organic optoelectronic materials, biotechnology, photochemistry, and so on, by changing spa...

In an attempt to reveal a new structure–property interplay between the relative cavity size of the host–guest nanohoop complexes and nonlinear optical (NLO) responses, a series of “Russian doll” co...

The nonlinear optical (NLO) and thermally activated delayed fluorescence (TADF) properties of organic push–pull materials consisting of π-conjugated electron-donating (D) and electron-accepting (A)...

The curved and electron-rich nature of buckybowls doped with heteroatoms makes them suitable electron-donating hosts for fullerene in the formation of concave–convex supramolecular complexes. The bowl depths of heteroatom-doped buckybowls are sensitive for the radius of the doping atoms. With the aim to investigate the influence of the bowl depth of the buckybowl and intermolecular interaction on the nonlinear optical (NLO) responses of complexes, the structures, binding interactions, electronic absorption spectra, and first hyperpolarizabilities (βtot) of the complexes formed by X-doped sumanene (X= Si, Ge, O, S, and Se) and C60 have been explored using density functional theory calculations. It is found that as doped atoms’ radii increase, the curvatures with shallower bowl depth of buckybowls and the distance between the base of C60 and buckybowls become increasingly smaller. However, atoms with larger radius tend to produce stronger binding energies between buckybowls and C60, accompanied with a gradu...

C2N monolayer has been proved to catalyze some important reaction, such as CO oxidation and N2 reduction reaction efficiently due to the periodic porous structure and the electron enrichment on nitrogen atoms. However the catalytic performance of C2N in CO2 reduction still needs comprehensive investigation. In this work, the potential of Cu atom embedded C2N monolayer (Cu/C2N), as a single-atom catalyst (SACs) for hydrogenation of CO2 to formic acid, has been evaluated by the first-principles calculations. The computational results show that the reaction can proceed via two feasible mechanisms, named as path I and path II, which start from the initial co-adsorption of H2 and CO2 on Cu/C2N (H2 + CO2@Cu/C2N) and H2 adsorption on Cu/C2N (H2@Cu/C2N), respectively. Path II exhibits the obvious superiority due to the low barrier all through the whole channel. The highest energy barrier in path II is only 0.53 eV, which means that CO2 hydrogenation to formic could be realized on the Cu/C2N at the room temperature. The high activity of the single atom catalyst Cu/C2N implies the potential application in the industrial CO2 hydrogenation. This study also promotes a new path to design catalysts for the reduction of CO2 and further broadens the range of applications for C2N-based materials.

Recently, exploration of stabler and lead-free perovskite absorbers with better cost-effective processability and prominent light-harvesting capacity has attracted extensive attentions. Inorganic C...

Interesting T- and V-shaped molecules consisting of donor (D) - acceptor (A) - donor (D) involving a new acceptor core of pyridoquinoxaline has been synthesized, and has attracted intensive research interest due to its intramolecular charge transfer (ICT) -driven thermally activated delayed fluorescence (TADF) and nonlinear optical effects (NLO) characteristics. In the present work, the structure and electronic properties of T- and V-shaped molecules under the gas phase and the solid-state environment are explored based on the combination of a nonempirical, optimally tuned range-separated hybrid functional with the polarizable continuum model (PCM): (1) The singlet-triplet gap (ΔEST) of all studied molecules in gas phase are reduced by an order of magnitude the solid-state environment, indicating they are potentially efficient TADF materials. (2) The ΔEST decrease in the solid state is attributed to the simultaneous presence of dominant 1CT and 3CT excited states under the solid-state polarization. (3) Compared with the T-shaped system, the V-shaped molecules can be dramatically enhanced NLO coefficient (βtot = 59.7 × 10−30 esu) in vacuum, which is due to the larger separate distributions of first hyperpolarizability density. (4) More importantly, the polarization effect effectively regulates and controls the NLO response of all studied molecules. The present work provides an effective strategy for developing the high-performance TADF and NLO materials by tuning the polarization effect and the connected style between D and A units.

On the basis of great diverse applications of nonlinear optical (NLO) materials, organometallic complexes have attracted considerable attention. In this paper, we present a detailed investigation on a series of Pt(II) dithienylcyclopentene(DTE)-based complexes via density functional theory method with the aim of evaluating their structures, electronic absorption spectra and first hyperpolarizabilities. The calculations demonstrate that the first hyperpolarizabilities can be enhanced by the introduction of quinolone into the complexes because of the enlarged spatial separation of electron density. However, Pt(II) complexes containing perfluorocyclopentene ring exhibit decreasing NLO response attributed to lower amount of charge transferred and short effective CT distance. The static first hyperpolarizabilities (βtot) of monometallic Pt(II) complexes are larger than those of bimetallic Pt(II) complexes due to correlative mixed charge-transfer patterns. More importantly, the closed-ring (1c) complex comprising DTE unit exhibits the largest βtot value approaching 144 × 10−30 esu, with the contrast over five times compared to corresponding open-ring due to the better π-conjugated delocalization and smaller HOMO and LUMO energy gap. In general, we envision our work will be beneficial for further rational design of DTE-containing Pt(II) complexes as high performance NLO materials.

Organic molecules consisting of electron donor (D) and electron acceptor (A) subunits linked by π-conjugated bridges are promising building blocks for thermally activated delayed fluorescence (TADF) and non-linear optics (NLO) materials due to their intramolecular charge transfer (CT) processes in response to external stimuli. According to the electron interaction pattern, the CT process in D–π–A architectures can be divided into two categories, through-bond/-space charge transfer (TB/TSCT). To date, research into the TADF properties of TSCT characteristic molecules has since seen significant growth. In fact, TSCT characteristic materials show great advantages in such NLO responses. In this perspective, we first briefly introduced the basic principles of NLO and TADF effects. Successively, we discuss the influence of TBCT and TSCT patterns on NLO and TADF properties, especially for TSCT characteristic. In the final part, we address the diversity and potential advantages of TSCT characteristic molecules as high-performance NLO materials. With these, it is expected that the greater structural flexibility of spatial conjugation can bring more functionality to NLO materials in the future.

Based on molecular structural design of boron-dipyrromethene (BODIPY), nine BODIPY derivatives decorated with vinyl, phenyl, dimethylamino, nitro and aldehyde group substituents, respectively, have been systematically investigated by the density function theory (DFT) method. The purposes of this paper are to study the effect of various substituents and their positions on geometric structures, electronic structures and second-order nonlinear optical (NLO) properties. In addition, the effects of polarizable environment and electric fields on the first hyperpolarizabilities (βtot) values have been investigated. It is found that the incorporation of strong electron-donating dimethylamino could induce a significant enhancement of the βtot values, and the βtot values of the bilateral α-position substitution are much larger with respect to the unilateral α-position substitution, because those substituents are able to expend the BODIPYs’ delocalized π-electron system to different extents. Time-dependent DFT results suggest that the increasement of the βtot values is related to the intramolecular charge transfer from substituents to BODIPY core. Thus, forming a D-π-A model is favorable for increasing the βtot values, where BODIPY was used as electron accepting. Hence, we hope this work will be beneficial to further investigating versatile and novel NLO materials.

Focusing on the remarkably various cyclometalated Pt(II) acetylcetonate complexes bearing an isomeric donor (D)–acceptor (A) conjugation framework ligand by virtue of adjusting the nitrogen atom coordination position, we have systematically investigated the geometric and electronic structures, redox properties, polarizabilities, first hyperpolarizabilities (βtot), and first hyperpolarizability densities of these intriguing isomeric Pt(II) complexes using density functional theory with the view to rationalizing the nonlinear optical (NLO) structure–function relationships. Our calculations demonstrated that modulating the coordination position that affects the intramolecular D–A interactions gives rise to large second-order NLO responses in the studied complexes, which are qualitatively elucidated in terms of the change in the charge transfer (CT) patterns using time-dependent density functional theory. In particular, for complex 2, coordination with the stronger electron donating capacity of triphenylamine and the electron-withdrawing ability of the [1,2,5]thiadiazolo[3,4-c]pyridine unit produces the highest βtot value (329 × 10−30 esu) owing to the obvious bidirectional CT transition, which is the most fascinating candidate for a NLO material among all of the investigated complexes. Significantly, a noteworthy finding was that remarkable βtot contrasts were observed for these isomeric Pt(II) complexes upon redox process, illustrating that they could be applicable for efficient redox-triggered NLO switches, especially using an oxidation stimulus with the highest on/off ratio, approaching 168.6 for complex 3. Furthermore, we have also quantitatively investigated the solid-state polarization effects on the βtot values for neutral complexes using the polarizable continuum model. Therefore, it can be anticipated that the present work may be advantageous to the experimental and theoretical design of novel smart cyclometalated Pt(II) complexes for functional NLO materials.

In an attempt to enrich the understanding of essential structure–nonlinear optical (NLO) property correlations in multi-component photoactive boron dipyrromethene/closo-dodecaborane/diketopyrrolopyrrole (BOD/Cp/DPP) hybrid chromophores, three basic modules, three dyads, and five triads were systematically designed and comparatively investigated. Herein, the geometric and electronic structures, electronic absorption spectra, polarizabilities (αave) and first hyperpolarizabilities (βtot) were calculated using density functional theory. It was found that the absorption spectrum and αave results of our current chromophores were highly modular, which can be efficiently deduced from the corresponding building blocks. The βtot values were determined by the BOD module because of their dominant polarization mechanisms, rather than a general dependence on the molecular size/volume. Furthermore, we presented a comprehensive assessment of the evolution of the structure and photophysical (NLO) properties upon linear combination of basic functional modules, one-/two-dimensional geometric differences and carborane's differently substituted position deriving from the pristine rod-like BOD–Cp–DPP platform. The take home messages suggest that the quadratic NLO behaviors can be rationally tuned by the minor modifications in the structure. Overall, we believe that the proposed chromophores and even more the reasoning for their design/recognition will be helpful for the exploration of more efficient NLO materials than those currently available.

Recently, extensive studies have widely fabricated and demonstrated that organic-inorganic hybrid perovskite-type solar cells, CH3NH3PbI3, have the superior optoelectronic properties. We explore the structural, electronic, optical properties and stability of tetragonal phase mixed halide perovskites CH3NH3Pb(I1-yXy)3 (X = Cl, Br; y = 0, 0.25, 0.5, 0.75), using first-principles calculations. The calculation of electronic structure reveals that the valance band maximum is governed by the halide p-orbitals and Pb 6s-orbitals while the conduction band minimum formed by the mixed contribution from the p orbitals of Pb atom and s orbitals of I atom. For the stability and optical properties of CH3NH3Pb(I1-yXy)3, the absorption coefficients show a blueshift of the absorption onsets but their stabilities show gradually increase with the increasing of X contents. Three different doping occupation phases of MAPb(I0.5X0.5)3 demonstrate that the impact of doping positions in linear optical property cannot be neglected but there is no change in stability. On the basis of all calculated results, we conclude that the best accouplement between absorption coefficiency and stability can be achieved at y = 0.25 in CH3NH3Pb(I1−yBry)3 perovskites.

Density functional theory (DFT) have been carried out to investigate the nine recently reported iridium (Ⅲ) complexes which substituted various cyclometalated ligands (CˆN) and aryl isocyanide ancillary ligands (CNAr). The aim of this paper is to study the substituents effect on geometrical structures, electronic and second-order nonlinear optical (NLO) properties, UV-vis absorption spectra. It is found that the first hyperpolarizabilities can be easily modulated by the introduction of different electron-withdrawing/donating ligands on CˆN and CNAr. Complexes with 2-benzothienylpyidine (btp) CˆN ligands or the substituents on CNAr are electron-withdrawing groups -NO2 possess larger first hyperpolarizabilities values compared to remaining complexes. Significantly, the changes of the first hyperpolarizability can be qualitatively explained by means of the charge transfer pattern. It is anticipative that the theoretical investigation of these iridium complexes will be helpful for designing high-performance and versatile NLO materials.

Recently, three 9,9-dimethylxanthene-based donor (D)/acceptor (A) U-shaped space-through architectures, containing π–π intramolecular interactions between the D and A, exhibit unique advantage (i.e., a small singlet (S1) – triplet (T1) energy splitting (ΔEST)) in thermally activated delayed fluorescence (TADF). To explore the TADF and second-order nonlinear optical (NLO) properties of U-shape compounds with through-space charge transfer (TSCT) between aligned D and A units compared with that of conventional conjugated D–A (L shape) ones, we theoretically investigated the geometric and electronic structures, through space D–A π–π interactions, CT properties, ΔEST, and first hyperpolarizabilities (βtot) of compounds 1-L∼5-U. The calculated ΔEST values of the U-shaped molecules are relatively smaller than that of L-shaped compounds in gas phase, indicating that the U-shaped derivatives are excellent thermally activated delayed fluorescent candidates. Furthermore, a noteworthy finding was that the conjugated ...

In view of the experimental observation of (H2)2@C70 and (H2O)2@C70, it has been suggested that hydrogen fluoride (HF) dimer can be completely localized within the sub-nanospace inside the fullerene C70 cage. With the aim of quantum chemical prospective of (HF)2@C70, electronic structure calculations of C60 hosting H2, HF, and H2O monomers, as well as C70 hosting H2, HF, and H2O monomers and dimers, were performed by using the density functional theory, together with the quantum theory of atoms in molecules, the natural population, and interaction energy calculation. The F–H···F bonding energy inside C70 was estimated at −13.25 kcal/mol, which is smaller than that of free dimer in the gas phase (−8.37 kcal/mol). Exploration of various featured properties suggests that (HF)2@C70 may be also regarded as a unique system composed of both inter- and intramolecular interactions like (H2)2@C70 and (H2O)2@C70. In addition, absorption spectroscopy and linear and nonlinear optical coefficients of C60 hosting H2, HF...

Recently, a benzothiazolyl group bearing the NO2S2-macrocycle L has been the subject of great interest due to its unique advantages in binding metal cations. Here, we systematically investigate the second-order nonlinear optical (NLO) properties of L, its metal cation derivatives L*M (M = Na+, K+, Mg2+, Ca2+, Zn2+, Cd2+, and Hg2+), and some anion-controlled complexes [Hg(L)(ClO4)2 and Hg(L)(Cl)2] by density functional theory (DFT). The results show that the addition of the transition metal cation Hg2+ leads to the increasing transition energy of the S0 → S1 transition, which induces a significant decrement in the NLO response (βtot = 8.2 × 10−30 esu) with respect to the corresponding macrocycle L (βtot = 125.8 × 10−30 esu). The depolarization ratio (DR) and anisotropy parameter (ρ) render it possible to control the NLO contribution. Further analysis of the charge transfer (CT) parameters, transferred electrons (qCT), CT distance (dCT), and t index indicates that L*Hg2+ reaches the minimum CT and spatial charge separation. Thus, the transition metal cation Hg2+ is distinguishable and easier to detect by utilizing the variations in the NLO response. Furthermore, the addition of ClO4− to the complex L*Hg2+ forms a distorted pentagonal bipyramid configuration, which drives the significant reduction of the first hyperpolarizability. Therefore, the obvious NLO contrasts can be switched by different metal cations and anions, which will broaden the scope of optical molecular detectors and further inspire us to investigate it.

Structural, electrical, and optical properties, as well as the thermal stability, of lead free mixed halide perovskites, Cs2InBr5-yXy·H2O (X = Cl, I; y = 0, 1, 2, 3, 4, 5) and Cs2InBr6-x·xH2O (x = 1, 2, 3, 4) were investigated using first principles calculation. The structural stability of all studied pervoskites has been estimated by the calculation of structural parameters, Goldschmidt tolerance factor, and the octahedral factor. The obtained band gap of I-doped Cs2InBr5-yIy·H2O systems are 2.049, 1.726, 1.581, 1.475 and 1.272 eV with y =1, 2, 3, 4, 5, lower than 2.391 eV of Cs2InBr5·H2O. The absorption spectra were also calculated to evaluate optical properties of Cs2InBr5-yXy·H2O, which presents an obvious red-shift for I-doped perovskites in the visible region, while a blue-shift for Cl-doped perovskites. The formation energies of Cs2InBr5-yXy·H2O were calculated and the obtained negative values determined their good thermodynamic stability, except Cs2InBrI4·H2O and Cs2InI5·H2O with the extremely small positive values. In addition, the influence of the amount of crystal water on the properties of Cs2InBr6-x·xH2O was also considered. The defect formation energies of Cs2InBr6-x·xH2O were calculated and the obtained negative values indicate their appropriate stability. In brief, Cs2InBr3I2·H2O and Cs2InBr4·2H2O are two optimal candidates among all the studied systems for the photovoltaic application. These results provide some ideas for understanding various properties of mixed halide perovskites.

Owing to the potential application in the development of new nonlinear optical (NLO) materials, metallomacrocycles have currently attracted considerable attention. The unusual 24 atoms {C16B8} cobaltacarborane ring 4, [Cp*Co(2,3-Et2C2B4H3-5-C≡C-7-C≡C)]4 (Cp* = η5-C5Me5), featured highly symmetrical, 2D planar, tetratruncated square architectures have been investigated and characterized compared to its 1D rod-like dinuclear building blocks 2a, [Cp*Co(2,3-Et2C2B4H3-7-C≡C)]2, 2b, [Cp*Co(2,3-Et2C2B4H3-5-C≡C)]2, and the 0D sandwich monomer 1, Cp*Co(Et2C2B4H4), by density functional theory. Calculations of geometric and electronic structures, UV–vis absorption spectra, polarizabilities (αave), and second hyperpolarizabilities (γtot) have been performed herein with the aim of rationalizing the structure–property relationship and providing a novel high-performance NLO molecular materials. It is found that the tetranuclear species present long-range bidirectional charge transfer behaviors, leading to an excellent ...

Ru metal acetylide electron donor-acceptor complexes have important applications in the field of nonlinear optics. Herein, in this work, a series of half-sandwich ruthenium-based Cp*(dpe)Ru ([Ru*]) metal complexes with the dihydroazulene/vinylheptafulvene (DHA/VHF) have been investigated by density functional theory (DFT) calculations. The results showed that the position of the [Ru*] acetylide functionality, either para or meta on the phenylene ring to the DHA/VHF core ( 1c/1o and 2c/2o ), and additional a p -phenylene spacer ( 3c/3o ) had a great influence on the second-order nonlinear optical (NLO) responses. The systems 1 and 3 can significantly increased second-order NLO responses compared with system 2 . It was attributed to the more obvious charge transfer along y -axis, which is from [Ru*] acetylide functionality to DHA, accompanied by a significant decrease of the transition energy according electron density difference maps and time-dependent DFT calculations. The β vec values of the open-ring complexes were larger than the corresponding closed-ring complexes owing to the smaller HOMO−LUMO gap in the open-ring complexes. It was also because of the smaller BLA values in open-ring complexes, which had stronger π-conjugation. Especially, the change ratio of β vec value of system 2 was the largest due to the fact that their charge transfers degree varied greatly. In addition, the frequency-dependent NLO properties of the studied complexes were evaluated at 0.0239 a.u. and 0.0340 a.u. The calculation results demonstrated that the magnitude of the frequency-dependent first hyperpolarizability increased with the increasing frequency. We believe that our present work will be beneficial for further theoretical and experimental studies on large second-order NLO responses of metal complexes.

Self-assembled donor–acceptor chromophores have extensive applications in photofunctional devices owing to their unique charge transport properties. To explore the possibility of improving nonlinear optical (NLO) properties by self-assembly to multilayer complexes, we theoretically investigated the geometric and electronic structures, interlayer weak interactions, absorption spectra, charge transfer properties, polarizabilities (α), and first hyperpolarizabilities (β) of naphthalimide, -phenyl, and -naphthyl monomers, dimers, and trimers by increasing the layer number n (n = 1, 2, 3). Different stacking patterns of their dimers were also taken into account. These show that parallel stacking patterns are conducive to maximizing overlap with respect to antiparallel ones due to the concept of optimal π-orbital overlap is more vast than purely maximizing cofacial overlap to improve charge transport. The decreases in band gap for the di/trimeric versus monomeric naphthalimide, -phenyl, and -naphthyl monomers i...

Most of the coumarins have been found useful as non-linear optical chromophores. The four novel water-soluble coumarin-based compounds (OC6, NC6, OC7, and NC7) and the metallic compounds of NC7 with different metal cations (Na+, K+, Mg2+, Ca2+, Fe2+, and Zn2+) have been investigated by carrying out density functional theory (DFT). Our DFT calculations revealed that the second-order nonlinear optical properties have a pronounced enhancement by means of the introduction of π-conjugatd electron donor (dimethylamino phenyl alkynyl) in 7-position of the coumarin ring and metal cations, especially for transition metals. The further investigations of the larger first hyperpolarizability (βtot) reveal that the NC7*Fe2+ and NC7*Zn2+ present the larger values as 1.151 × 10−27 and 1.083 × 10−27 esu owing to the lower transition energies and larger oscillator strengths of crucial electronic transitions. Moreover, time-dependent DFT results show that the large intramolecular charge transfers exist in the NC7*Fe2+ and NC7*Zn2+. In addition, the natural bond orbital analysis demonstrated that the second-order stabilization energies is from the lone pair (LP) orbital on O atom to the LP* orbital of metal cations interaction correlate with the O-Mn+ atomics distance. On the other hand, the atoms in molecules analysis showed that the O-Mn+ interactions can be characterized by the presence of a bond critical point (BCP) and the O-Fe2+ and O-Zn2+ interactions have partially ionic and partially covalent bonds rather than an electrostatic character for O-Mn+ (Na+, K+, Mg2+ and Ca2+). In addition, the delocalization indices of O-Mn+ bonds correlate reasonably well with electron density, kinetic and potential energy densities in these complexes. Thus, we hope this research will introduce a new relation between the structure and the property of chromophore nonlinear optical activity.

Metal–bridged polcyclic aromatic complexes, exhibiting unusual optical effects such as near-infrared photoluminescence with particularly large Stokes shifts, long lifetimes and aggregation enhancement, have been established as unique “carbonloong chemistry”. Herein, the electronic structures, aromaticities, absorption spectra and third order nonlinear optical (NLO) responses of metal–bridged polcyclic aromatic complexes (M = Fe, Re, Os and Ir) are investigated using the density functional theory computations. It is found that the bridge–head metal can stabilize and influence rings, thus creating π–, σ– and metalla–aromaticity in an extended, π–conjugated framework. Interestingly, metal radius greatly influence the bond, aromaticity, liner and third order NLO properties, which reveals useful information to develop new applications of metal regulatory mechanism in NLO materials field. Significantly, the novel relationship between the aromaticity and third order NLO response has firstly been proposed, that the metal-bridged polycyclic complex with larger aromaticity will exhibit larger third order nonlinear optical response. It is our expectation that the novel link between aromaticity and NLO response could provide valuable information for scientists to develop the potential NLO materials on the basis of metal–bridged polycyclic complexes.

To provide a new approach for enhancing second-order nonlinear optical (NLO) response, a series of multinuclear “staircase” oligomers composed of Fe(Et2C2B4H4) ferracarborane clusters and benzene rings have been systematically designed and investigated. The calculations of geometric and electronic structures, electronic absorption spectra, first hyperpolarizabilities, and first hyperpolarizability densities were carried out by density functional theory and time-dependent density functional theory. It is found that the NLO properties have obvious multiple relationships with the numbers of the sandwich unit. Moreover, all of the possibilities for one-, two-, and three-electron oxide complexes have also been considered. The results first revealed some remarkable changes upon charge transfer pattern which is from the unexpected “interrupted” to desired “continuous” forms in the two-electron oxidation reactions, accompanied by significant differences in the relevant second-order NLO properties. The considerabl...

A family of hydrazone-based photochromic derivatives consisting a hydrazone switching and phenyl groups with R1 and R2 (R = H, -NO2 and -NMe2) 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 (βtot) 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 (ΔEge) and the narrower energy band gap (Egap) of frontier molecular orbital. Furthermore, the push-pull complexes 4 may be potential NLO materials due to the larger βtot values, for example, the βtot 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.

Spirooxazine, a photochromic material, can transform into metallic open-form merocyanine by molecular switching, giving rise to large contrasts in its second-order nonlinear optical (NLO) properties. The switching properties are particularly large when various metal ions (Li+, Na+, K+, Mg2+, Ca2+, Fe2+, Zn2+, and Ag+) are introduced, as evidenced by density functional theory calculations, which show that the spirooxazine undergoes a pronounced change in geometry accompanied by formation of a larger π-conjugated system. The resultant merocyanine derivatives have 10–21-fold higher static second-order NLO responses. Spirooxazine can therefore be used as a powerful and multi-use detection tool. The large first hyperpolarizability (βtot) is shown to rely on the alkaline earth metal, causing βtot values to increase nearly 21-fold, as evidenced by the larger charge distribution, lower transition energy, and separate distribution of first hyperpolarizability density. In contrast, variation of βtot in the Fe2+ derivative is not obvious, owing to stronger complexation, a larger amount of charge transferred from the napthoxazine moiety to the metal, and the reduction in N⋯O distance between the ligand heads. Therefore, spiropyran-to-merocyanine molecular switching can be used to distinguish alkaline earth metals and determine the efficiency of cation detection.

Confining excess electrons in a specific space is an effective strategy to design nonlinear optical (NLO) molecules. The complexants with excess electrons are usually organic compounds, but these compounds are thermally unstable and thus hardly meet the processing requirements of NLO materials. To obtain better thermostability and NLO response molecules, in this work, inorganic compounds of B20H26 isomers containing two cavities were proposed. With the two included cavities, B20H26 can be doped by one or two Li atoms to form electrides of Li@B20H26 and Li2@B20H26. These electrides show larger NLO responses, with respect to the corresponding undoped complexant of B20H26. Particularly, Li2@B20H26 has the largest β0 value of 108846 a.u. (MP2/6-31+G(d) level) that is 850 times as large as that of corresponding B20H26. Moreover, the change of β0 values with excess electron number is remarkable for two of the isomers, and differences between the β0 values among those isomers are also significant owing to various B–B connection sites between the two cavities. Therefore, the present inorganic electrides have not only better performance due to the magnitude of their β0 values but also better behavior on the molecular-level modulation of NLO.

To reveal a new structure–property relationship regarding the nonlinear optical (NLO) properties of fullerenes that are associated with gamma (γ) density, fullerenes I (C40, C50, C60 and C70), whose heights range from 4.83 to 7.96 A, and II (C24, C36, C48 and C72), whose widths range from 4.45 to 8.22 A, have been the research objects. Calculation of their geometric and electronic structures, absorption spectra, and the second hyperpolarizability (γ) and the γ density analysis have been performed. It is found that the electronic spatial extent and the polarizability (α) value increase linearly as the fullerenes increase by every 12 carbon atoms. Similarly, the γ values are also proportional to the fullerene size. It is worth noting that the relative magnitude of γxxxx and γzzzz was exactly consistent with that of the width and height of fullerenes. The analysis of γ density provides the essential reason for this result, that is, the magnitude of the contribution to γ values associated with γ densities is proportional to the density amplitudes multiplied by the distance between them. Larger fullerenes possess larger density amplitudes and longer distances, resulting in larger γ values with respect to smaller fullerenes. This work presents a new structure–property interplay between the width and height of the fullerenes and their second hyperpolarizability γ. Moreover, the γ density analysis provides a new insight to explore the nature of the relationship between the structure and the NLO properties.

The size-selective formation of eight molecular recognition pairs between the host corannulene and fullerene guest of various size have been studied by taking advantage of concave–convex π–π interactions. Herein, the structures, binding interactions, electronic absorption spectra, and first hyperpolarizabilities have been explored using density functional theory calculations. It is found that with the aim to maximize the concave–convex shape complementarity, the base of fullerene can be modified at certain angles with the central ring plane of C20H10 (0° for complexes 1–4 and 46°, 34°, 19°, and 5° for complexes 5–8, respectively). The interaction energies depend linearly on the convex surface area and the size of the fullerene sphere. Further, the results of first hyperpolarizabilities show that the shape of the fullerene is the dominant factor for complexes 1–4 because of the intramolecular charge transfer (CT) within fullerene cage. Among them, complex 4 presents the largest βtot value as 5.64 × 10–30 e...

ABO2-type perovskite materials have been wide applied in solid oxide fuel cells and gas sensors. SrFeO2 with P4/mmm structure exhibiting an unparalleled FeO4 square-planar coordination structure. We have investigated the Sr-site substitution effect on the electronic conductivity of the perovskite-type structure of (Sr1−xCax)FeO2 and (Sr1−xBax)FeO2 (x = 0, 0.25, 0.5, 0.75) by using first-principle calculations. Six kinds of doping form have been considered for the Ca-site and Ba-site, respectively. The different doping concentration and position lead to change in crystal structure and electronic properties. When x = 0.5, α and β doping structures display Pmmm symmetry, while γ and δ doping structures show P4/mmm symmetry. The band structure and density of states reveal that different doping concentration and position can make the electronic conductivity change from semiconductor to semi-metallic. When x = 0.25, 0.75, 0.5 for γ and δ doping, the doped system were semi-metallic properties. Whereas, when x = 0.5 for α and β doping, the doped system were semiconductor properties. Further, doping can lead to an increase of the magnetic moments. It is worth noting that the Ca-doped system has higher growth in the magnetic moments compare with the Ba-doped system. This work provides a new route for the potential application in electrochemistry devices.

Complex 1 [( Ph I 2 P 2− ) AlCl] was widely applied in advanced materials due to its interesting structure. Two Square-planar (SP) complexes 2 [( Ph I 2 P 2− ) GaCl] and 3 [( Ph I 2 P 2− ) NiCl] together with SP complex 1 have been investigated by density functional theory. The results indicate that the interaction between M (M = Al, Ga, Ni) and L ( Ph I 2 P 2− ) are not typical true two-electron three-center interactions but a mixture of electronic and covalent. The presence of covalent bond character between M and L is supported by the localized orbital locator, electron localization function and energy decomposition analysis. Further, we also predicted the absorption spectrum of complexes 1 – 3 by time-dependant density functional theory. The results of absorption spectrum shows a red-shift trend from complexes 1 , 2 to 3 . Investigation of the bond interaction at the molecular level can benefit the design and preparation of such SP complexes in chemistry and materials science.

The push-pull functionalized fullerenes consisting of multi-N,N-diethylamine donors covalently attached to N-methylpyrrolidine derivative of C60 have been designed and investigated. The structures and first hyperpolarizabilities of these fullerene derivatives were calculated using density functional theory. Furthermore, absorption spectra of the complexes along with electron density difference maps corresponding to the most intense electronic transitions were achieved by time-dependent density functional theory. It suggests that with the growing numbers of N,N-Dimethylanilin acting as electron-donating group, the polarizabilities, dipole moments and the first hyperpolarizabilits increase, however, transition energies of the crucial electronic transitions decrease and the absorption wavelength shows bathochromic effect. The excitation transitions have significant charge transfer character and, as a consequence, the novel complexes can behave as second-order nonlinear optical chromophores, in which the N,N-Dimethylanilin act as donors towards fullerenes.

Carborane has been the subject of great interest over the last decades due to its high structural, chemical, biological stability and diverse applications. In the present work, carboranyl-substituted indole/indoline compounds and their functionalized derivatives have been systematically investigated by density functional theory (DFT) method with the view of assessing their electronic structures and first hyperpolarizabilities. Significantly, the first hyperpolarizabilities can be obviously enhanced by the introduction of a strong electron-withdrawing group for closed-ring forms, while the strong electron-donating group is beneficial for large first hyperpolarizabilities for open-ring forms. It indicates that the NLO properties of these compounds can be enhanced by controlling their relative substituent groups. Furthermore, the time-dependent DFT calculation illustrates that the enhancement of the first hyperpolarizabilities are found due to the obvious charge transfer (CT) transition, and closed-ring forms have a significant difference on the CT patterns versus open-ring ones. Investigation of the structure-property relationship and substituent effects at the molecular level can benefit for further exploration of carboranyl-substituted indole/indoline derivatives with versatile and fascinating NLO properties.

The control of rotational motion, using an external impulse (such as redox), has been intensively pursued as nonlinear optics switch. Four redox responsive ferrocene-based actuators with varied π-conjugated units have been systematically investigated by the density functional theory. The open structures of these complexes with antiparallel orientation of both π-conjugated units are due to the large charge repulsion effect, while the closed forms are stabilized by the intramolecular π–π stacking interactions. The rotational motion can be triggered by reduction process preferentially centered on the π-conjugated units. The polarizabilities and first hyperpolarizabilities of complexes [ 3 ] closed 2 + and [ 4 ] closed 2 + are significant enhanced, which are respectively related to the electronic spatial extent and intramolecular interlayer charge transfer occurred between two respective π-conjugated units. Overall, the present work shows that one can design the molecular nonlinear optical switches characterized by a large contrast varying from zero to a large value along the reversible transformations.

Ion-buckybowl complexes have received considerable attention in modern chemical research due to its fundamental and practical importance. Herein, we performed density functional theory (DFT) to calculate the geometical structure, binding interactions, dipole moments and the first hyperpolarizabilities (βtot) of ion-buckybowl complexes (ions are Cl(-) and Na(+), buckybowls are quadrannulene, corannulene and sumanene). It is found that the stabilities of ion-buckybowl compounds primarily originate from the interaction energy, which was proved by a new isomerization energy decomposition analysis approach. Plots of reduced density gradient mirror the ion-π weak interaction has been formed between the ions and buckybowls. Significantly, the buckybowl subunits cannot effectively impact the nonlinear optical (NLO), but the kind of ion has marked influence on the second-order NLO responses. The βtot values of Cl(-)-buckybowl complexes are all larger as compared to that of Na(+)-buckybowl complexes, which is attributed to the large charge-transfer (CT) from Cl(-) to buckybowl. Our present work will be beneficial for further theoretical and experimental studies on the NLO properties of ion-buckybowl compounds.

Towards the computational design of single-atom alloys (SAAs) catalysts, we systematically studied the hydrogen activation, spillover and desorption by density functional theory (DFT) and first-principles calculations. Herein, we designed a model with 27 individual isolated metals in Cu(111) slab and described the scaling relationships and meticulous electronic structures. The results show that CuPd, CuMn, CuPt SAAs possess appropriate H atom binding ability and lower H2 dissociation barrier superior to pure metal Cu. There have been many reports about the design of hydrogenation catalysts before, but most of them are about CuPd and CuPt SAAs. Here we found that CuMn SAAs exhibits excellent catalytic performance, even comparable to CuPd and CuPt SAAs. Based on exhaustive electronic structure analysis, we discovered a rare electronic structure on CuMn SAAs, where Mn has no obvious electronic interaction with the host metal Cu, even like a free atom. The incredible phenomenon promotes CuMn SAAs to possess extraordinary hydrogenation catalytic activity. This paper seeks to provide deep insights into chemistry, catalysis, and interfaces for people to design new catalysts.

A photoswitchable heteroditpioc ion-pair receptor E-1 and its isomeride Z-1 (without the anion binding site), that are based on the 2-pyridyl acylhydrazone linking 2,6-pyridine bisamide, have brought our attention to systematically explore the second-order nonlinear optical (NLO) properties by the density functional theory (DFT). In this work, we mainly studied the influences of metal cations (M = Na+, K+, Mg2+, Ca2+, Hg2+ and Pb2+), anions (X = Cl−, Br− and I−) and ion-pair (NaCl, NaBr and NaI) on NLO responses for the receptor. In addition, the impacts of isomerization and poto-switching processes on NLO response for these systems also have been discussed detailedly. The results show that the isomerization process does not effectively adjust the NLO properties for our studied systems. But the poto-switching process that was triggered by light to capure or release ions plays an important role in improving the NLO properties. The receptors E-1 and Z-1 are excellent candidates to effectively detect metal cation Pb2+, because the first hyperpolarizability (βtot) values of E∗Pb2+ and Z∗Pb2+ increased by 13 times and 20 times relative to that of receptors E-1 (188.06 a.u.) and Z-1 (270.21 a.u.), respectively. In addition, the receptor E-1 has the possibility to detect anion I− due to the larger βtot values compared with other anion-complexes. However, the changes of NLO responses for ion-pair complexes are not obvious compared with corresponding anion-complexes. We are looking forward to the research would be beneficial for further theoretical and experimental studies on recognizing metal cations and anions based on large second-order NLO difference.

Density functional theory (DFT) calculations have been carried out to investigate the switching of the second-order nonlinear optical (NLO) properties of iridium(III) complexes. The aim of this paper is to calculate the substituent effect and redox effect on geometrical and electronic structures, redox center, UV–Vis absorption spectra and second-order nonlinear optical (NLO) properties. It is found that changing β-diketiminate ancillary ligand have little effect on first hyperpolarizabilities values, but the redox process can significantly enhance the second-order NLO responses. The βtot values of 1+, 2+ and 3+ oxidation states of the complexes are about 10.2 times, 19.7 times and 25.5 times larger than their corresponding neutral complexes, respectively. The βtot values of the complexes in their various reduction states 1-, 2- and 3- are about 13.2 times, 35.0 times and 8.5 times larger than neutral complexes, respectively. The complexes in their various reduction or oxidation states display larger first hyperpolarizabilities than neutral complexes due to the remarkable bathochromic shift of maximal absorption and the decrease of related transition energies. The theoretical investigation of these iridium complexes will be helpful for providing a fundamental guideline and reference for further research for novel NLO materials.

It is crucial to explore the best active center for a catalyst in heterogeneous catalysis. Here we probe the performance of B single-atom doped Cu catalyst and the corresponding pure metal catalyst in water-gas shift reaction (WGSR) through density functional theory (DFT). The results show that Cu catalyst modified by B single-atom obtained unprecedented catalytic property compared to the corresponding pure metal catalyst, which is due to the special active site for water dissociation that the embedded B single-atom creates two heterogeneous Cu atoms with different electronic structures. Moreover, due to its charming electronic property, B atom can act as a charge transfer medium, freely switching between anionic and cationic states. More importantly, the synergy of heterogeneous Cu atoms reduces the activation energy barrier of the rate-limiting step (water dissociation) by 0.11 eV on B-doped Cu surface in WGSR. Electronic structure analysis emerges a downshifted d-band center of surface Cu atoms coordinated with B atom and an upshifted d-band center of those by Cu-Cu coordination originated from strain and ligand effects. The findings aim to provide deep insights for people to design new catalysts using earth-abundant elements in WGSR.