Intraligand Charge Transfer Research Articles

Synthesis, Characterization and Complexation Behaviour of Chloroquine towards Ti (II) Ion

Aims: Chloroquine is a member of the drug class 4-aminoquinoline used for the prevention and treatment of malaria in areas where malaria is known to be sensitive to its effects.
 Our aim is to synthesize the chloroquine – titanium complex and to study its coordination behavior.
 Place and Duration of Study: Department of Chemistry, Michael Okpara University of Agriculture, Umudike, 2019.
 Methodology: Ti(II) complex of chloroquine was synthesized by the reaction of chloroquine phosphate with titanium(IV) oxide. The metal complex was characterized based on UV, IR and 1H NMR Spectroscopy.
 Results: The UV spectrum of the complex suggested intra ligand charge transfer (ILCT), ligand to metal charge transfer (LMCT), and d-d transition. The IR spectrum of the complex showed the involvement of amine and imine group in coordination to Ti. This showed that chloroquine acted as a bidentate ligand. 1H NMR of the spectrum further showed the involvement of the amine group in coordination.
 Conclusion: The ability of chloroquine to sequestrate Ti (II) ion has been assured. This drug can be used to chelate Ti ions from solution, environment, and biological system.

Fabrication of a water-stable luminescent MOF with an open Lewis basic triazolyl group for the high-performance sensing of acetone and Fe3+ ions

A 3D chemically stable MOF of {[Cd1.5(DBPT)(DiPyDz)(H2O)]·3.5H2O}n (1) was successfully synthesized by a hydrothermal process, with the help of multifunctional ligand of H3DBPT (3-(3,5-dicarboxylphenyl)-5-(4-carboxylphenyl)-1-H-1,2,4-triazole) and bridging ligand of 1,2-di(pyridine-4-yl)diazene (DiPyDz). Characterizations of PXRD, FT-IR, TG and PL analysis for compound 1 were implemented. The overall structure maintains thermally stable up to 354 °C and keeps structural stability in common solvents after 48 h immersion. Most strikingly, it could maintain the crystallinity in water even for 10 days. It exhibits strong emission peak centered at 412 nm upon excitation at 280 nm, which could be attributed to the intra-ligand charge transfer of the H3DBPT ligand. It has proved itself an efficient sensor not only for acetone at low concentration but also for Fe3+ ion. The detection limit is estimated to be 0.0013% (v/v%) for the acetone, and 78 ppb for the Fe3+ ion, respectively. The KSV value for sensing Fe3+ ion is calculated to be 4.78 × 105 M−1, which is the third top one among the reported excellent MOFs-based sensors. The sensing performance is not affected even in the existence of interference metal ions, which reflects the high application potentials for the effective detection of Fe3+ in an aqueous system.

Crystalline network study of new N-phthaloyl-β-Alanine with benzimidazole, cocrystal: Computational consideration & free radical scavenging activity

The new cocrystal adducts of N-phthaloyl-β-alanine and benzimidazole (1:2) with molecular formula C18H15N3O4 (1) was synthesized by slow evaporation process of the aqueous solution containing the two said moieties. The confirmation of proposed formula can be established through crystal structure as well as FTIR analysis. The crystal structure was confirmed by single X–ray crystal analysis. The experimental and theoretical studies of photophysical properties like Fourier Transform Infrared (FTIR) and ultraviolet–visible spectroscopy (UV–Vis) have been done. The cocrystal belong to monoclinic crystallographic system with space group P21/c, Z = 4. DPPH radical scavenging activity of the title cocrystal is slightly lower than coformer with lower IC50 value, respectively. One dimensional infinite chain in direction of [010] parallel to b direction. Optimized crystalline network structure of 1 shows that conventional N−H⋯O, and OH⋯N, and the non−conventional CH⋯O hydrogen bonds (HBs) gathered the monomeric components of 1 (1−mon). The reliable calculations of the dispersion corrected density functional theory (DFT−D) display that N−H⋯O and O−H⋯N HBs more share in the stabilization of the network structure. The theoretical study of UV–Vis spectra in solvents (water, acetonitrile, methanol, and n–heptanes) confirms the experimental results as seven main bands in 180–270 nm range. They could attribute to intra-ligand charge transfer (ILCT) as benzimidazole → benzimidazole and N-phthaloyl-β-alanine → N-phthaloyl-β-alanine with π → π* character.

Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl-Dithiolene Promoting Pyran Cyclization.

Mononuclear Mo and W enzymes require a unique ligand known as molybdopterin (MPT). This ligand binds the metal through a dithiolene chelate, and the dithiolene bridges a reduced pyranopterin group. Pyran scission and formation have been proposed as a reaction of the MPT ligand that may occur within the enzymes to adjust reactivity at the Mo atom. We address this issue by investigating oxo-Mo(IV) model complexes containing dithiolenes substituted by pterin or quinoxaline and a hydroxyalkyl poised to form a pyran ring. While the pterin-dithiolene model complex exhibits a low energy, reversible pyran cyclization, here we report that pyran cyclization does not spontaneously occur in the quinoxalyl-dithiolene model. However, protonating the quinoxalyl-dithiolene model induces pyran cyclization forming an unstable, pyrano-quinoxalyl-dithiolene complex which subsequently dehydrates and rearranges to a pyrrolo-quinoxlyl-dithiolene complex that was previously characterized. The protonated pyrano-quinoxalyl-dithiolene complex was characterized by absorption spectroscopy and cyclic voltammetry, and these results suggest pyran cyclization leads to a significant change in the Mo electronic structure exhibited as a strong intraligand charge transfer (ILCT) transition and 370 mV positive shift of the Mo(V/IV) reduction potential. The influence of protonation on quinoxaline reactivity supports the hypothesis that the local protein environment in the second coordination sphere of molybdenum cofactor (Moco) could control pyran cyclization. The results also demonstrate that the remarkable chemical reactivity of the pterin-dithiolene ligand is subtly distinct and not reproduced by the simpler quinoxaline analog that is often used to replace pterin in synthetic Moco models.

Metal-organic frameworks based on magnesium(ii): adsorption and luminescence properties

Two new metal-organic frameworks based on magnesium(ii) ions, [Mg4(bdc)3(dma)6(NO3)2]•DMA (1; bdc is 1,4-benzenedicarboxylate; dma, DMA is N,N-dimethylacetamide) and [Mg3(bpdc)3(nmp)4] (2; bpdc is 4,4´-biphenyldicarboxylate; nmp is N-methylpyrrolidone), were synthesized in DMA or NMP, respectively. According to the single-crystal X-ray diffraction data, compound 1 is built of binuclear carboxylate units {Mg2(O2CR)3}, which were previously not observed in metal-organic frameworks. Compound 2 is based on trinuclear carb oxylate units {Mg3(O2CR)6}. Compound 1 has a layered structure (hcb topology), whereas compound 2 has a distorted three-dimensional cubic structure (pcu topology). The phase purity and chemical identity of the compounds were confirmed by IR spectroscopy, thermogravimetry, elemental analysis, and powder X-ray diffraction. Photoluminescence properties of both compounds are indicative of intraligand charge-transfer transitions of one (for 1) or two (for 2) types. Textural characteristics of an activated sample of 1 were measured by nitrogen and hydrogen adsorption at 77 K and by carbon dioxide adsorption at 195 K.

Alkali Blues: Blue-Emissive Alkali Metal Pyrrolates.

2-Iminopyrroles [HtBu L, 4-tert-butyl phenyl(pyrrol-2-ylmethylene)amine] are non-fluorescent π systems. However, they display blue fluorescence after deprotonation with alkali metal bases in the solid state and in solution at room temperature. In the solid state, the alkali metal 2-imino pyrrolates, M(tBu L), aggregate to dimers, [M(tBu L)(NCR)]2 (M=Li, R=CH3 , CH(CH3 )CNH2 ), or polymers, [M(tBu L)]n (M=Na, K). In solution (solv=CH3 CN, DMSO, THF, and toluene), solvated, uncharged monomeric species M(tBu L)(solv)m with N,N'-chelated alkali metal ions are present. Due to the electron-rich pyrrolate and the electron-poor arylimino moiety, the M(tBu L) chromophore possesses a low-energy intraligand charge-transfer (ILCT) excited state. The chelated alkali cations rigidify the chromophore, restricting intramolecular motions (RIM) by the chelation-enhanced fluorescence (CHEF) effect in solution and, consequently, switch-on a blue fluorescence emission.

Solvent effect on the solubility and absorption spectra of meloxicam: experimental and theoretical calculations

ABSTRACTThe solubility and absorption spectra of meloxicam (MLX) in 18 pure solvents were determined. In addition, molecular modelling calculations were performed. MLX presents the lowest solubility in water and the highest in dioxane. The results indicate that the polarity/polarisability of the solvent, and the Hildebrand’s solubility parameter, have a greater influence on its solubility. The MLX absorption spectra show that a redshift occurs when the solvent polarity increases. By applying Kamlet-Taft and Catalán methods it has been suggested that the solvent polarisability is the most important solvent´s parameter in the solvatochromism of MLX. The electronic transitions were determined using the TD-DFT methodology with the B3LYP, PBE0 and LC-wPBE functional. The best results were obtained with PBE0. Also, it was determined that the main MOs responsible for the electronic transition are HOMO → LUMO with a ππ* character with a significant intraligand charge transfer from the thiazole to the oxycam group.

Formation of Hetero-binuclear Pt(II)-M(II) Complexes Based on (2-(1 H-Tetrazol-5-yl)phenyl)diphenylphosphine Oxide for Superior Phosphorescence of Monomers.

Novel hetero-binuclear platinum complexes (HBC-Pt(II)-M(II), M = Ca(II), Mg(II), Zn(II), and Cd(II)) have been synthesized by the reaction of the corresponding precursors [Pt(ppy)(μ-Cl)]2 with (2-(1 H-tetrazol-5-yl)phenyl)diphenylphosphine oxide (TTPPO). The X-ray structures of the complexes show that two ancillary ligands TTPPO in the square-planar Pt(II) moiety act as a quadridentate chelating agent for the other metal center, eventually forming a distorted octahedral configuration. There are no significant π-π interactions and Pt-M metallophilic interactions in the crystal lattice, due to the steric hindrances associated with the rigid octahedral structure together with the bulky TTPPO. Consequently, HBC-Pt-M complexes show monomer emission characteristics with quantum yields up to 59% in powder, suggesting their great potential for practical applications. DFT and TD-DFT calculations on HBC-Pt-Zn reveal that the phosphorescence can be ascribed to intraligand charge transfer (3ILCT) combined with some metal-to-ligand charge transfer (3MLCT) in the Pt(ppy) moiety, which is consistent with the observations from the photophysical investigations.

Heteroleptic Ir(III)N6 Complexes with Long-Lived Triplet Excited States and in Vitro Photobiological Activities.

A series of cationic heteroleptic iridium(III) complexes bearing tris-diimine ligands [Ir(phen)2(R-phen)]3+ (R-phen = phenanthroline (1), 3,8-diphenylphenanthroline (2), 3,8-dipyrenylphenanthroline (3), 3-phenylphenanthroline (4), 3-pyrenylphenanthroline (5), and 3,8-diphenylethynylphenanthroline (6)) were synthesized and characterized. These complexes possessed phen ligand-localized 1π,π* transitions below 300 nm, and charge transfer (1CT) and/or 1π,π* transitions between 300 and 520 nm. In 1, 2, 4, and 6, the low-energy bands were mixed 1CT/1π,π*. However, the increased π-donating ability of the pyrenyl substituent(s) in 3 and 5 split the low-energy bands into a pyrene-based 1π,π* transition at 300-380 nm and an intraligand charge transfer (1ILCT) transition at 380-520 nm. All complexes were emissive at room temperature in CH3CN, but the parentage of the emitting state varied depending on the R substituent(s). Complex 1 exhibited predominantly phen ligand-localized 3π,π* emission mixed with metal-to-ligand charge transfer (3MLCT) character, whereas the emission of 2, 4, and 6 was predominantly from the excited-state with 3π,π*/3ILCT/3MLCT character. The emission from 3 and 5 was dominated by pyrene-based 3π,π* states mixed with 3ILCT character. The different natures of the lowest triplet excited states were also reflected by the different spectral features and lifetimes of the triplet transient absorption of these complexes. Complexes 3 and 5 had singlet oxygen quantum yields as high as 81 and 72%, respectively. Both gave submicromolar phototoxicities toward cancer cells (SK-MEL-28 human melanoma) and bacteria ( S. aureus and S. mutans) with visible-light activation (and marginal to no photobiological activity with red light). Their visible-light phototherapeutic indices (PIs) toward SK-MEL-28 cells were 248 for 3 and >435 for 5; PIs were lower in bacteria (≤62) because of their inherent antimicrobial activities. Both complexes were shown to produce substantial amounts of intracellular reactive oxygen species (ROS), which may account for their photobiological activities.

Photophysical properties of structural isomers of homoleptic Ir-complexes derived from xylenyl-substituted N-heterocyclic carbene ligands.

The phosphorescence properties of fac-Ir(pmp)3, mer-Ir(pmp)3, fac-Ir(dmpmp)3 and mer-Ir(dmpmp)3 (where pmp = 3-methyl-1-phenyl-2,3-dihydro-1H-imidazo[4,5-b]pyridine and dmpmp = 1-(2',6'-dimethylbiphenyl-2-yl)-3-methyl-2,3-dihydro-1H-imidazo[4,5-b]pyridine) in CH2Cl2 were investigated. At 77 K, the fac-isomers showed blue emission with a vibronic structure, while the mer-isomers showed less structured emissions. At 300 K, all complexes showed broad and markedly red-shifted emission spectra compared to those at 77 K. The quantum yields of the Ir(dmpmp)3 isomers were very low, and their emission lifetimes were very short compared to those of Ir(pmp)3. In order to understand the large differences between the photodynamic properties of Ir(pmp)3 and Ir(dmpmp)3, we performed femtosecond time-resolved transient absorption (TA) spectroscopic measurements. The TA spectra of Ir(dmpmp)3 were almost the same as those of Ir(pmp)3 at a short delay time. However, Ir(dmpmp)3 showed a new broad TA band at around 720 nm with increasing delay time. The rise time of this band was ca. 10 ps for both isomers, and this may be attributed to the geometrical change in the excited state, which is associated with the steric hindrance of the bulky dimethylphenyl substituent. Actually, Ir(dmpmp)3 showed a strong rigidochromic shift in the emission spectra with varying temperature. To understand the molecular orbitals and the energy levels, theoretical calculations were performed using density functional theory. As a result, structural displacement takes place accompanied by the fast migration of localization of excited states via intraligand charge transfer.

Luminescent Sensing, Selective Extraction and Recovery of Cu2+ from Aqueous Environment by a Novel Turn-on Chemosensor.

A novel luminescent hydrazone ligand was synthesized via 1:1 condensation reaction of 9-anthracene aldehyde and 2-hydrazinobenzoic acid followed by its characterization with the help of absorption, emission, FTIR, NMR and mass studies. It was investigated as a reversible, ratiometric and turn-on luminescent chemosensor for Cu2+ in aqueous environment. The receptor shows a prominent color change in presence of Cu2+ from yellow to reddish brown in DMSO-H2O (2:1) medium. Upon addition of Cu2+, a remarkable increment in emission intensity (Φ = 0.091, 11 fold) was observed probably due to intra-ligand charge transfer transition (ILCT). Interestingly, this sensor is capable to extract Cu2+ selectively from aqueous mixture of metal ions using dichloromethane solvent with the increased extraction efficiency from 85% (L:Cu2+, 1:1) to 95% (L:Cu2+, 2:1) in the pH range of 6.5-10.0. The extraction behavior of Cu2+ was monitored with the help of UV-Vis spectroscopy and a readily-usable smartphone to capture the RGB data which may be helpful as a field based analysis tool. In presence of Cu2+ (1.0 × 10-5M), no significant interference was observed after addition of 5-fold excess of other metal ions (Zn2+, Cd2+, Co2+, Fe2+, Fe3+, Ni2+, Hg2+, Sn2+, Al3+, Cr3+, Mn2+) in DMSO-H2O (2:1) medium. Moreover, the ligand was regenerated (> 98%) by adjusting the pH upto 4cycles and showed a good recyclability and reusability which might be helpful to extract Cu2+ efficiently from aqueous medium.

Quantum-Chemical Insights into the Phosphorescence Efficiencies of Blue-Emitting Platinum Complexes with Phenylene-Bridged Pincer Ligands.

Blue phosphorescent platinum complexes with phenylene-bridged pincer ligands, [Pt(dmib)Cl] [1; dmib = m-bis(methylimidazolyl)benzene], [Pt(mizb)Cl] [2; mizb = bis( N-methylimidazolium)benzene], and [Pt(dpzb)Cl] [3; dpzb = m-bis(3,5-dimethylpyrazolyl)benzene], have been investigated theoretically to rationalize the marked differences of their phosphorescence efficiencies. On the basis of density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, the geometrical and electronic structures, absorption and emission properties, and radiative and nonradiative processes are analyzed in detail. The emission from the emissive lowest triplet state (T1) originates from a mixture of metal-to-ligand charge-transfer (3MLCT) and intraligand charge-transfer (3ILCT) states. The calculated radiative decay rate constants of T1 of the complexes are comparable and in the same order of magnitude with the experimental measurements. Therefore, the potential energy profiles for the deactivation processes from T1 via temperature-independent and -dependent pathways are explored to reveal the effect of nonradiative decay on phosphorescence. The calculated results indicate that the very weak emission of 3 could be ascribed to the deactivation process via the metal-centered (3MC) state, which can be readily accessible via a spontaneous process from the T1 state. This work provides more in-depth insight into the nature of the emissive excited state, shielding light on a better understanding of the excited-state behavior of phosphorescent platinum complexes.

Amino-Substituted 2,2'-Bipyridine Ligands as Fluorescent Indicators for ZnII and Applications for Fluorescence Imaging of Prostate Cells.

ZnII concentrations in malignant prostate tissues are much lower than in benign or healthy, suggesting that ZnII levels are a potential biomarker for prostate cancer (PCa). Five 2,2'-bipyridine ligands were synthesized containing amino substituents with varying electron-donating ability for investigation as fluorescent ZnII indicators. The excited state characteristics of the ligands were explored by UV/Vis and fluorescence spectroscopy. 3,3'-Diamino-2,2'-bipyridine (1) was previously shown to be weakly fluorescent as a result of π→π* transitions. The other four ligands have properties consistent with an n→π* intraligand charge transfer excited state. Strongly donating amino and aminophenyl (2 and 4) substituents gave low quantum yields, while weaker donating benzimidazole substituents (6 and 7) gave high quantum yields. Absorption and fluorescence wavelengths underwent bathochromic shifts upon ZnII binding in a majority of cases. Quantum yields drastically increased upon ZnII binding for 1 and 2, but decreased for 4, 6, and 7. Compounds 6 and 7 were incubated with PC-3, DU 145 and BPH-1 cells to determine their ZnII sensing abilities in a biological system. Weak fluorescence was observed in BPH-1 cells and subsequent incubation with ZnII caused fluorescence intensity to increase. No fluorescence was observed in PCa cell lines. Further investigation of these ligands may allow for quantitative determination of ZnII concentrations in ex vivo tissue samples.

Robust and Long-Lived Excited State Ru(II) Polyimine Photosensitizers Boost Hydrogen Production

The prototypical [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine, Ru-1) with 3MLCT state (metal-to-ligand charge-transfer, πM → πL*) is one of the most widely used photosensitizers (PSs) for photocatalytic hydrogen production. However, its photostability and excited state lifetime (<1 μs) are eagerly to be improved to further enhance the performance of hydrogen production. Herein, [Ru(bpy)2(3-pyrenyl-1,10-phenanthroline)]2+ (Ru-3) with 3IL/3MLCT equilibrated state and [Ru(bpy)2(3-pyrenyl ethynylene-1,10-phenanthroline)]2+(Ru-4) with 3IL state (intraligand charge transfer, πL → πL*) as lowest excited state were first introduced into the photocatalytic hydrogen evolution system. Photophysical and photocatalytic characteristics manifest that the 3IL state complex (Ru-4) shows a long-lived excited state (up to 120 μs) and much enhanced photostability with no photobleaching over 13 h in stark contrast to Ru-1 and [Ru(bpy)2(1,10-phenanthroline)]2+ (Ru-2). Photocatalytic reactions with these Ru(II) complexes as PSs, Co(dmgH...

Polyphenylcyclopentadienyl Ligands as an Effective Light-Harvesting π-Bonded Antenna for Lanthanide +3 Ions.

A new approach to design "antenna-ligands" to enhance the photoluminescence of lanthanide coordination compounds has been developed based on a π-type ligand-the polyphenyl-substituted cyclopentadienyl. The complexes of di-, tri-, and tetraphenyl cyclopentadienyl ligands with Tb and Gd have been synthesized and all the possible structural types from mononuclear to di- and tetranuclear complexes, as well as a coordination polymer were obtained. All types of the complexes have been studied by single-crystal X-ray diffraction and optical spectroscopy. All terbium complexes are luminescent at ambient temperature and two of them have relatively high quantum yields (50 and 60%). Analysis of energy transfer process has been performed and supported by quantum chemical calculations. The role of a low-lying intraligand charge transfer state formed by extra coordination with K+ in the Tb3+ ion luminescence sensitization is discussed. New aspects for design of lanthanide complexes containing π-type ligands with desired luminescence properties have been proposed.

The Use of Cyclometalated NHCs and Pyrazoles for the Development of Fully Efficient Blue PtII Emitters and Pt/Ag Clusters.

New bis-pyrazole complexes [Pt(C^C*)(RpzH)2 ]X, containing a cyclometalated N-heterocyclic carbene ligand (HC^C*=1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene) were prepared as chloride (X=Cl- , RpzH: 3,5-Me2 pzH 1 a, 4-MepzH 2 a, pzH 3 a), perchlorate (X=ClO4- , 1 b-3 b), or hexafluorophosphate (X=PF6- , RpzH: 3,5-Me2 pzH 1 c) salts. The X-ray structure of 1 a showed that the Cl- anion is trapped by the cation through two N-H⋅⋅⋅Cl bonds. In solution of methanol, acetone and THF at RT, 1 a-3 a coexist in equilibrium with the corresponding [PtCl(C^C*)(RpzH)] (B) and RpzH species. In CH2 Cl2 , this equilibrium takes place just for 2 a and 3 a, but it is completely shifted to the left at 243 and 223 K for 2 a and 3 a, respectively. The low-lying absorption and emission bands were assigned to intraligand (ILCT) charge transfer on the NHC group. Quantum yield measurements in PMMA films revealed that 1 b, 2 b and 1 c are amongst the most efficient blue-light emitters, with values up to 100 %. Proton abstraction from the coordinated 3,5-Me2 pzH in 1 b by NEt3 and replacement by Ag+ afforded a neutral [Pt2 Ag2 ] cluster containing Pt→Ag dative bonds.

The Effect of Pyrazolyl Substituents on the Photophysical and Photochemical Properties of Pyrazine Derivatives.

The reaction of 2,5-dibromopyrazine with N-Lithium pyrazolate in a 1:2 ratio leads to a mixture of 2-bromo-5-(1H-pyrazol-1-yl)pyrazine (I) and 2,5-di(1H-pyrazol-1-yl)pyrazine (II). The structures of I and II are highly planar. Two absorption bands can be observed for the compounds in the UV-Vis region, having ε in the order of 104 m-1 cm-1 . TD-DFT computed results support the nature of the lower energy absorptions as πpyrazine →π*pyrazine transitions, including an additional intraligand charge transfer transition for I (πpyrazol →π*pyrazine ). Upon excitation at 280 or 320nm, the emission of both compounds is almost not affected by solvent polarity or oxygen presence, showing two bands for I and one for II in the 350-450nm region. Emission of II follows a mono-exponential decay, while I decays following a bi-exponential law, hypothesized from πpyrazine →π*pyrazine and πpyrazol →π*pyrazine transitions. Photodegradation of I and II follows a first-order kinetic with constants of 1.18×10-2 min-1 and 0.13×10-2 min-1 , respectively. Results suggest that photodegradation of I starts with the loose of bromide followed by intermolecular pyrazolyl subtraction and ring opening. This path is not available for II, which is reflected in its enhanced photostability.

Cu(II) ion based 1D coordination polymer: Its thermal, fluorescence properties, Hirshfeld surface analysis and theoretical calculations

ABSTRACTIn this investigation, the reaction of [Cu(2,2′-bpy)(H2O)4][ClO4]2 with thiosemicarbazide (tsc) yielded [Cu(2,2′-bpy)(NCS)2]n frameworks, which has crystallized in noncentrosymmetric space group (Cc). The complex has been characterized by elemental analyses, FT-IR spectrum, powder X-ray diffraction analysis and single-crystal diffraction analysis. This complex is 1D polymer with high thermal stability and showing positive cotton effect. These results have provided some interesting insights into its nonlinear optical applications. Solid state fluorescence spectrum shows broad photoluminescence emission bands, which are assigned as the bands of intra-ligand charge transfer and MLCT (metal to ligand charge transfer) transitions. During investigation of various intermolecular interactions, both single crystal X-ray diffraction and Hirshfeld surface analysis give comparable results.

Dramatic Alteration of 3ILCT Lifetimes Using Ancillary Ligands in [Re(L)(CO)3(phen-TPA)] n+ Complexes: An Integrated Spectroscopic and Theoretical Study.

The ground and excited state photophysical properties of a series of fac-[Re(L)(CO)3(α-diimine)] n+ complexes, where L = Br-, Cl-, 4-dimethylaminopyridine (dmap) and pyridine (py) have been extensively studied utilizing numerous electronic and vibrational spectroscopic techniques in conjunction with a suite of quantum chemical methods. The α-diimine ligand consists of 1,10-phenanthroline with the highly electron donating triphenylamine (TPA) appended in the 5 position. This gives rise to intraligand charge transfer (ILCT) states lying lower in energy than the conventional metal-to-ligand charge transfer (MLCT) state, the energies of which are red and blue-shifted, respectively, as the ancillary ligand, L becomes more electron withdrawing. The emitting state is 3ILCT in nature for all complexes studied, characterized through transient absorption and emission, transient resonance Raman (TR2), time-resolved infrared (TRIR) spectroscopy and TDDFT calculations. Systematic modulation of the ancillary ligand causes unanticipated variation in the 3ILCT lifetime by 2 orders of magnitude, ranging from 6.0 μs for L = Br- to 27 ns for L = py, without altering the nature of the excited state formed or the relative order of the other CT states present. Temperature dependent lifetime measurements and quantum chemical calculations provide no clear indication of close lying deactivating states, MO switching, contributions from a halide-to-ligand charge transfer (XLCT) state or dramatic changes in spin-orbit coupling. It appears that the influence of the ancillary ligand on the excited state lifetime could be explained in terms of energy gap law, in which there is a correlation between ln( knr) and Eem with a slope of -21.4 eV-1 for the 3ILCT emission.

Theoretical Exploration of the Layered Sandwich Cobaltacarborane as a Multi-State NLO Molecular Switch Triggered by Redox

Layered sandwich metallacarboranes have various advantages including structural diversity, tailoring ability, rich electrochemical properties, and high thermal stability and thus could be potential multifunctional nonlinear optical (NLO) materials. In this study, second-order NLO properties and the multi-state switching effect of the layered cobaltacarborane, induced by electrochemical behavior, were explored using density functional theory (DFT). The calculated first hyperpolarizabilities (β) illustrated that the NLO responses are enhanced with the increasing of layers, which was mainly attributed to the C → B intraligand charge transfer (C2B3) (ILCT) and metal-centered d → d transition (MCT) as indicated by the time-dependent (TD)DFT results. Remarkable β contrasts were observed after undergoing two sequential one-electron redox processes. Therefore, the pronounced multi-state NLO switch can be achieved. In mixed-valence systems, the metal–metal interaction plays a crucial role in the NLO responses thro...