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

Inorganic electrides of alkali metal doped Zn12O12 nanocage with excellent nonlinear optical response

Finding new materials with exceptionally large nonlinear optical response is an interesting and challenging avenue for scientific research. Here, we report the alkali metal doped Zn₁₂O₁₂ nanocages as inorganic electrides with excellent nonlinear optical response. Density functional theory calculations have been performed for geometric, electronic and nonlinear optical response of exo- and endohedrally alkali metal doped Zn₁₂O₁₂ nanoclusters. For exohedral doping, all different possible doping sites are considered for decoration of alkali metal on the nanocage. The electride nature of the complexes is highly dependent on the position of alkali metal doping. All exohedral complexes except for alkali metal doping on six membered ring (r₆) are electride in nature, as revealed from frontier molecular orbital analysis. Interaction energies reveal that all doped nanoclusters except endo-K@Zn₁₂O₁₂ are thermodynamically stable. The exothermic encapsulation of alkali metals in Zn₁₂O₁₂ nanocages is in marked contradiction with other inorganic fullerenes where encapsulation is an endothermic process. The barriers for boundary crossing are also evaluated in order study the interconversion of exo- and endohedral complexes. Doping of alkali metal significantly influences the properties of nanocages. HOMO-LUMO (H-L) gap is reduced significantly whereas hyperpolarizability is increased several orders of magnitude. The NLO response of exohedrally doped complexes is higher than the corresponding endohedral complexes, which is in mark contradiction with the behavior of phosphide or nitride nanocages. The highest first hyperpolarizability of 1.0 × 10⁵ au is calculated for K@r₆-Zn₁₂O₁₂ complex. Third order NLO response of these complexes is calculated and compared with the best systems reported in the literature at the same level of theory.

Tuning the Liquid Crystallinity of Cholesteryl-o-Carborane Dyads: Synthesis, Structure, Photoluminescence, and Mesomorphic Properties

A set of mesomorphic materials in which the o-carborane cluster is covalently bonded to a cholesteryl benzoate moiety (mesogen group) through a suitably designed linker is described. The olefin cross-metathesis between appropriately functionalized styrenyl-o-carborane derivatives and a terminal alkenyl cholesteryl benzoate mesogen (all type I terminal olefins) leads to the desired trans-regioisomer, which is the best-suited configuration to obtain mesomorphic properties in the final materials. The introduction of different substituents (R = H (M2), Me (M3), or Ph (M4)) to one of the carbon atoms of the o-carborane cluster (Ccluster) enables the tailoring of liquid crystalline properties. Compounds M2 and M3 show the chiral nematic (N*) phase, whereas M4 do not show liquid crystal behavior. Weaker intermolecular interactions in the solid M3 with respect to those in M2 may allow the liquid crystallinity in M3 to be expressed as enantiotropic behavior, whereas breaking the stronger intermolecular interaction in the solid state of M2 leads directly to the isotropic state, resulting in monotropic behavior. Remarkably, M3 also displays the blue phase, which was observed neither in the chiral nematic precursor nor in the styrenyl-cholesterol model (M5) without an o-carborane cluster, which suggests that the presence of the cluster plays a role in stabilizing this highly twisted chiral phase. In the carborane-containing mesogens (M2 and M3), the o-carborane cluster can be incorporated without destroying the helical organization of the mesophase.

Cyclometalated Ir(III) Complexes with Curcuminoid Ligands as Active Second-Order NLO Chromophores and Building Blocks for SHG Polymeric Films

The second-order nonlinear optical (NLO) properties of iridium(III) complexes having two cyclometalated 2-phenylpyridines and curcumin or tetrahydrocurcumin as ancillary ligand have been investigated both in solution and as guest in a polymeric organic matrix. In solution, these complexes are characterized by a significant second-order NLO response, as determined by the Electric Field Induced Second Harmonic (EFISH) technique, like the related complex with acetylacetonate. Whereas the low second-harmonic generation response of a composite film of [Ir(2-phenylpyridine)2(acetylacetonate)] in polymethyl methacrylate was not stable and fell down to zero upon turning off the electric field. A good and stable response was obtained with a film based on the iridium(III) complex bearing two cyclometalated 2-phenylpyridines and curcumin.

An Unprecedented Family of Luminescent Iridium(III) Complexes Bearing a Six-Membered Chelated Tridentate C^N^C Ligand

A new family consisting of three luminescent neutral Ir(III) complexes with the unprecedented [Ir(C^N^C)(N^N)Cl] architecture, where C^N^C is a bis(six-membered) chelating tridentate tripod ligand derived from 2-benzhydrylpyridine (bnpy) and N^N is 4,4'-di-tert-butyl-2,2'-bipyridine (dtBubpy), is reported. X-ray crystallography reveals an unexpected and unusual double C-H bond activation of the two distal nonconjugated phenyl rings of the bnpy coupled with a very short Ir-Cl bond trans to the pyridine of the bnpy ligand. Depending on the substitution on the bnpy ligand, phosphorescence, ranging from yellow to red, is observed in dichloromethane solution. A combined study using density functional theory (DFT) and time-dependent DFT (TD-DFT) corroborates the mixed charge-transfer nature of the related excited states.

The influence of Sc doping on structural, electronic and optical properties of Be12O12, Mg12O12 and Ca12O12 nanocages: a DFT study

Density functional theory (DFT) calculations were used to study the effect of scandium doping on the structural, energetic, electronic, linear and nonlinear optical (NLO) properties of Be₁₂O₁₂, Mg₁₂O₁₂ and Ca₁₂O₁₂ nanoclusters. Scandium (Sc) doping on nanoclusters leads to narrowing of their E _g, which enhances their conductance greatly. Also, the polarizability (α) and first hyperpolarizability (β₀) of nanoclusters were dramatically increased as Be, Mg or Ca atoms are substituted with a Sc atom. Among all clusters, α and β₀ values for Sc-doped Ca₁₂O₁₂ were the largest. Consequently, the effect of the doping atom, as well as of cluster size, on electronic and optical properties was explored. Time dependent (TD)-DFT calculations were also carried out to confirm the β₀ values; the results show that the higher value of first hyperpolarizability belongs to Sc-doped Ca₁₂O₁₂, which has the smallest transition energy (ΔEgn). The results obtained show that these clusters can be candidates for using in electronic devices and NLO materials in industry.

Ion-π interaction in impacting the nonlinear optical properties of ion-buckybowl complexes

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.