Search

An approach to the design of highly emissive salen–indium complexes is presented. A series of 4-NR2-appended salen ligands possessing an electron-accepting 1,2-dicyanoethylene bridge and their indium complexes (R = Me (1), Et (2), and Ph (3)) were prepared in high yields via a one-pot synthetic pathway. All compounds exhibited narrow-bandwidth red emission (full width at half maximum = 29–42 nm) with high photoluminescence quantum yields (PLQYs, 50%−74%) in toluene. Specifically, 4-NEt2-appended indium complex 2 showed the highest PLQY of 74%, which is among the highest reported for salen-based organometallic luminophores. In contrast, reference complex 4 lacking a 4-amino group was poorly emissive (PLQY < 2%). Theoretical studies suggest that the salen-centered electronic transitions in 1–3 are enhanced by strong electronic interactions between the 4-amino donor and the electron-accepting bridge.

A π-extended, diaza-triphenylene embedded, mono-anionic corrole analogue and its Ni(II)-complex were synthesized from a diaza-triphenylene precursor, which was obtained from a double one-carbon insertion into a naphthobipyrrole diester. Following conversion to the corresponding activated diol and acid-catalyzed condensation with pyrrole and subsequent reaction with pentafluorobenzaldehyde, afforded mono-anionic, π-extended bipyricorrole-like macrocycle. Attempted Ni(II) insertion with Ni(OAc)2•4H2O resulted an ESR active, Ni(II) bipyricorrole radical complex, which is converted to stable cationic Ni(II) complex upon treatment with [(Et3O)+(SbCl6)-]. Both complexes were characterized by 1H- and 13C-NMR, UV-vis spectroscopy and single crystal X-ray diffraction analysis. The Ni(II) bipyricorrole radical complex is converted to cationic Ni(II) complex by single electron reduction using cobaltocene. Both cationic Ni(II) complex and radical Ni(II) complex exhibit ligand-centered redox behavior while the Ni(II) remains in the +2 oxidation state.

The impact of the electronic effect of the carbazole group on the radiative decay process based on the intramolecular charge transfer (ICT) transition of closo-o-carborane was examined herein. Four...

The conversion of closo-o-carborane–containing compounds to the nido-o-species via deboronation causes photophysical changes that could be used for sensing applications. 9-Methyl-9H-carbazole–based closo- (closo-Cz) and nido-o-carboranyl (nido-Cz) compounds were prepared and fully characterised by multinuclear NMR spectroscopy and elemental analysis, and the solid-state molecular structure of closo-Cz was analysed by X-ray crystallography. Although the closo-compound exhibited an emissive pattern centred at λem = ca. 530 nm in the rigid state only (in THF at 77 K and as a film), nido-Cz demonstrated intense emission in the near-UV region (λem = ca. 380 nm) in both solution and film states at 298 K. The positive solvatochromic effect of nido-Cz and the results of theoretical calculations for both the o-carboranyl compounds supported that these emissive features originate from intramolecular charge transfer (ICT) corresponding to the o-carborane. Furthermore, the calculations verified that the electronic role of the o-carboranyl unit changed from acceptor to donor upon deboronation from closo-Cz to nido-Cz. Investigations of the radiative decay mechanisms of closo-Cz and nido-Cz according to their quantum efficiencies (Φem) and decay lifetimes (τobs) suggested that the ICT-based radiative decays of closo-Cz and nido-Cz readily occur in the film (solid) and solution state, respectively. These observations implied that the emission of closo-Cz in the solution state could be drastically enhanced by deboronation to nido-Cz upon exposure to an increasing concentration of fluoride anions. Indeed, turn-on emissive features in an aqueous solution were observed upon deboronation, strongly suggesting the potential of closo-Cz as a turn-on and visually detectable chemodosimeter for fluoride ion sensing.

Molecular dynamics (MD) simulations with the umbrella sampling (US) method were used to investigate the properties of micelles formed by sodium lauryl ether sulfate with two ether groups (SLE2S) and behaviors of corresponding surfactants transferring from micelles to ceramide and DMPC bilayer surfaces. Average micelle radii based on the Einstein-Smoluchowski and Stokes-Einstein relations showed excellent agreement with those measured by dynamic light scattering, while those obtained by evaluating the gyration radius or calculating the distance between the micelle sulfur atoms and center of mass overestimate the radii. As an SLE2S micelle was pulled down to the ceramide bilayer surface in a 400 ns constant-force steered MD (cf-SMD) simulation, the micelle was partially deformed on the bilayer surface, and several SLE2S surfactants easily were partitioned from the micelle into the ceramide bilayer. In contrast, a micelle was not deformed on the DMPC bilayer surface, and SLE2S surfactants were not transferred from the micelle to the DMPC bilayer. Potential of mean force (PMF) calculations revealed that the Gibbs free energy required for an SLE2S surfactant monomer to transfer from a micelle to bulk water can be compensated by decreased Gibbs free energy when an SLE2S monomer transfers into the ceramide bilayer from bulk water. In addition, micelle deformation on the ceramide bilayer surface can reduce the Gibbs free energy barrier required for a surfactant to escape the micelle and help the surfactant partition from the micelle into the ceramide bilayer. An SLE2S surfactant partitioning into the ceramide bilayer is attributed to hydrogen bonding and favorable interactions between the hydrophilic surfactant head and ceramide molecules, which are more dominant than the dehydration penalty during bilayer insertion. Such interactions between surfactant and lipid molecule heads are considerably reduced in DMPC bilayers owing to dielectric screening by water molecules deep inside the head/tail boundary between the DMPC bilayer. This computational work demonstrates the distinct behavior of SLE2S surfactant micelles on ceramide and DMPC bilayer surfaces in terms of variation in Gibbs free energy, which offers insight into designing surfactants used in transdermal drug delivery systems and cosmetics.

An efficient protocol for the hydroboration of imines is reported. Lithium halide salts are effective catalysts to convert aldimines and ketimines to their corresponding amines. Here, we report excellent isolated yield of secondary amines (>95%) using 3 mol% lithium bromide in THF at room temperature. In addition, DFT calculations for a plausible reaction pathway are reported.

Two spiro[acridine-9,9′-fluorene]-based closo-o-carboranyl compounds, namely p-SAC and o-SAC, were prepared and fully characterized. p-SAC exhibited a weak high energy emission trace only in tetrahydrofuran (THF) at 298 K, while the photoluminescence (PL) spectra at 77 K exhibited intense emission in the low energy region. However, o-SAC exhibited an excellent dual-emissive pattern in THF at both 298 and 77 K. The electronic transition in each excited state (S1) was calculated, which confirmed that the high and low energy emission originated from locally excited (LE) states on the fluorene moieties and intramolecular charge-transfer (ICT) transitions corresponding to o-carboranes, respectively. All these characteristics indicated that ICT-based radiative decay was only favored in the rigid state, where structural fluctuations were restricted. Energy barriers were calculated based on relative energies at various dihedral angles around the o-carborane cages in p-SAC and o-SAC. The rotational motion of the o-carborane cage was less restricted in p-SAC when compared to o-SAC, resulting in suppression of the ICT-based emission when p-SAC was in solution. The PL experiments in the THF/water mixtures indicated that these features were caused by the aggregation-induced emission (AIE) effect. An acetonitrile solution containing relatively high concentrations of o-SAC (ca. 10−3 M) exhibited a dramatic emission color change from deep red to sky blue when the temperature was increased. The higher temperature caused a natural conversion from a colloidal state (slightly aggregated) to a clear solution. Consequently, the photophysical features of p-SAC and o-SAC demonstrated the application potential of π-aromatic conjugated o-carboranyl compounds as visual sensory materials.

Two o-carboranyl compounds containing 1,2,4-triazole groups, each appended with an N-aryl ring (either N-phenyl or N-diisopropylphenyl), were strategically designed and prepared to elucidate the relationship between their structural orientation (planarity) and intramolecular charge transfer (ICT)-based radiative decay. The photophysical analysis of both compounds shows that the N-phenyl appended compound shows a much higher quantum yield and larger radiative decay constant for ICT-based emission in the rigid state (solution at 77 K and film) than those of the N-diisopropylphenyl appended compound, even exhibiting an additional ICT-based emission in solution at 298 K. Theoretical calculations on their ground and excited states indicate that the planarity of the N-aryl appended triazole moiety affects the efficiency of radiative decay for the ICT transition. These findings firmly establish a strong relationship between the planarity of the appended aryl groups relative to the triazole ring and ICT-based radiative decay in these o-carboranyl luminophores.

Three closo-o-carborane-functionalised pyrene compounds (1CB, 2CB, and 4CB) were synthesised and fully characterised. The molecular structures of all compounds exhibited perpendicularity between the C–C bond of the o-carborane and the pyrene groups. The three compounds displayed major absorption bands assignable to π–π* transitions within the pyrene group, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carborane units and the pyrene moieties. While 1CB and 4CB displayed strong ICT-based emissions involving the o-carborane moiety (λem = 500–700 nm) in THF at 298 K, 2CB showed less intense LE-based emissions centred at λem = 407 nm. Although the PL spectra of all compounds demonstrated enhanced ICT-based emission via inhibition of C–C bond variance within the o-carborane in rigid states (THF at 77 K and films), the quantum efficiency of 2CB in films (Φem = 5%) did not significantly increase compared to that in THF at 298 K, while the values for 1CB and 4CB in films were dramatically enhanced to 75% and 62%, respectively. The radiative decay constants of each ICT-based emission showed that non-radiative decay processes were significantly larger for 2CB than in 1CB and 4CB. The relative energies of the various S0 conformations as the dihedral angle between the o-carborane cage and pyrene unit was changed indicated that the o-carborane cages in 2CB could rotate more easily than those in 1CB and 4CB. Furthermore, the involvement of the o-carborane moiety in the LUMO level of 2CB was significantly affected by this dihedral angle. These results suggest that the free rotation of the o-carborane cage of 2CB interrupted its ICT transitions, with experimental and theoretical findings confirming that large structural variations around the o-carborane cage for 2CB also induced ICT-based non-radiative decay processes associated with the o-carborane, further blocking the ICT transition itself.

The catalytic hydroboration of aldimines was demonstrated, with only 3 mol% NaH required for the quantitative production of secondary amines under minimal solvent conditions. In addition, chemoselective hydroboration in the presence of other reducible functional groups was achieved. DFT calculations were then used to propose a reaction mechanism for imine hydroboration.

9,9'-Spirobifluorene-based closo-o-carboranyl (SFC1 and SFC2) compounds and their nido-derivatives (nido-SFC1 and nido-SFC2) were prepared and characterized. The two closo-compounds displayed major absorption bands assignable to π-π* transitions involving the spirobifluorene group, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their spirobifluorene moieties. The nido-compounds exhibited slightly blueshifted absorption bands resulting from the absence of the ICT transitions corresponding to the o-carborane moieties due to the anionic character of the nido-o-carboranes. While SFC1 exhibited only high-energy emissions in THF at 298 K (only from locally excited (LE) states assignable to π-π* transitions on the spirobifluorene group), remarkable emissions in the low-energy region were observed in the rigid state such as in THF at 77 K and in the film state. SFC2 displayed intense emissions in the low-energy region in all states. The fact that neither of the nido-derivatives of SFC1 and SFC2 exhibited low-energy emissions and the TD-DFT calculation results of each closo-compound clearly verified that the low-energy emission was based on ICT-based radiative decay. The conformational barriers from each relative energy calculation upon changing the dihedral angles around the o-carborane cages for both compounds confirmed that the rotation of the o-carborane cages and terminal phenyl rings for SFC1 is freer than that for SFC2.

An approach to the design of a series of quinolinol-based indium complexes that can exhibit different optical properties is proposed. Mono-incorporated (Inq1 and InMeq1), bis-incorporated (InMeq2), and tris-incorporated (Inq3 and InMeq3) indium quinolinate complexes have been prepared. These complexes have also been characterized by X-ray crystallography. The photophysical properties of these complexes have also been examined by a combination of experimental and theoretical techniques. The indium complexes with a single quinolinol ligand (Inq1 and InMeq1) showed higher quantum efficiency than those with two or three quinolinate ligands; in particular, InMeq1 exhibited the highest quantum yield [ΦPL = 59% in poly(methyl methacrylate) film]. The insights into the nature of these findings were obtained by the sequential synthesis of the quinolinol-based indium luminophores and a detailed investigation of their structural stability.

The conversion of

A series of triphenylamine (TPA)-containing salen-Al assembly dyads, [salen(3- tBu-5-R)2Al(OC6H4- p-N(C6H5)2)] [salen = N, N'-bis(salicylidene)ethylenediamine; R = H (D1), tBu (D2), Ph (D3), OMe (D4), and NMe2 (D5)], were prepared in good yield (50-80%) and fully characterized by NMR spectroscopy and elemental analysis. Both the UV/vis absorption and photoluminescence (PL) spectra of D1-D4, except for D5, in a tetrahydrofuran solution exhibited dual patterns, which are assignable to the salen-Al-centered π-π* transition (low-energy region) and the TPA-centered π-π* transition (high-energy region). In particular, the emission spectra of the dyads displayed interesting dual-emissive patterns via a significant intramolecular energy transfer (IET) process between the salen-Al moiety and TPA group. Notably, this IET process was systematically tuned by varying the substituents and dominantly observed in the rigid state. More interestingly, compared to the salen-Al complexes (A1-A4) without the TPA group, D1-D4 exhibited enhanced quantum efficiencies. Time-dependent density functional theory calculations on the S1-optimized structures of D1-D5 further supported these experimental results by indicating the existence of independent transition states between the salen-Al moiety and TPA group in the assembly dyads. The present study reports the first example of salen-Al complexes bearing electron-rich TPA moieties.

Pyrazinoindole-based Lewis-acid/base assemblies are prepared through the use of regioselective formal [3 + 3] cycloaddition reactions, and their intriguing photophysical properties are described. The assemblies exhibit strong emissions in THF solution, which are attributed to through-space intramolecular charge-transfer (ICT) transitions between the branched Lewis-acid/base moieties. Furthermore, these show ratiometric color-change responses in PL titration experiments, which give rise to new colors through turn-on emissions ascribable to ICT transitions that alternate between the pyrazinoindole units and each triarylboryl or amino moiety, a consequence of the binding of the fluoride or acid. Pieces of filter paper covered by these assemblies exhibited blue-shifted color changes when immersed in aqueous acidic solutions, suggesting that these are promising candidate indicators that detect acid through emissive color. Computational data for these assemblies and their corresponding adducts verify the existence of ICT transitions that alternate through fluoride or acid binding.

Lithium diisobutyl-tert-butoxyaluminum hydride (LDBBA)-catalyzed hydroboration of alkynes with pinacolborane (HBpin) was demonstrated. The hydroboration proceeded more efficiently with LDBBA than with other aluminum hydrides and afforded alkenyl boronates in moderate to good yields. In addition, high-yielding LDBBA-catalyzed hydroboration of imines was achieved. The coordination of anionic aluminate with lithium enables effective hydride transfer for hydroboration.

To clarify the relationship between planarity and intramolecular charge transfer (ICT), two o-carboranyl compounds (TCB and FCB) containing different ortho-type terphenyl rings, namely, perfectly distorted or planar phenyl rings, were synthesised and fully characterised. Although the emission spectra of both compounds presented intriguing dual-emission patterns in solution at 298 or 77 K and in the film state, distorted TCB mostly showed locally excited emission, whereas planar FCB demonstrated intense emission corresponding to an ICT transition. Interestingly, the emission efficiencies and radiative decay constants of terphenyl-based o-carboranyl compounds were gradually enhanced by increasing the planarity of the terphenyl groups. These results verify the existence of a strong relationship between the planarity of appended aryl groups and ICT-based radiative decay in o-carborane-substituted compounds.

2-Phenylpyridine- and 2-(benzo[b]thiophen-2-yl)pyridine-based (ppy- and btp-based) o-carboranyl (Car1 and Car2) and their B(CH3)2-C∧N-chelated (Car1B and Car2B) compounds were prepared and fully characterised by multinuclear NMR spectroscopy and elemental analysis. The solid-state structure of Car2B was determined by single-crystal X-ray diffraction, which revealed a four-coordinated dimethylboryl centre. All compounds displayed major absorption bands that were assigned to π-π* transitions involving the ppy and btp moieties, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their aryl groups. Furthermore, the chelated compounds exhibited dominant low-energy absorption bands (λabs = 333 nm for Car1B and 383 nm for Car2B) resulting from the reinforcement of ICT transitions that correspond to the o-carborane moieties through the restriction of aromatic-ring free rotation. While Car1 and Car2 did not exhibit photoluminescence emissions in toluene at 298 K, Car1B and Car2B showed intense emissions, which are assignable to π-π* transitions associated with each chelated aryl group. However, Car1 and Car2 evidently emitted at around 450 nm in solution at 77 K, invoked by radiative ICT transitions between the carborane and the ppy or btp moiety, indicating that ICT-based radiative decay is only invigorated in the rigid state in the absence of structural variations, such as C-C bond fluctuations in the carborane cage and aromatic-ring free rotation. Interestingly, while Car1 in the film state exhibited a weak ICT-based emission spectrum, and Car1B and Car2B showed intense emissions originating from π-π* transitions associated with each chelated aryl group, Car2 showed significantly enhanced emissions in the same energy region as that exhibited in solution at 77 K, resulting in a much larger quantum efficiency over that in solution. DFT-optimised structures of Car1 and Car2 in their ground and the first-excited states clearly reveal that the enhanced emissive features of Car2 in the film state are strongly associated with the retained planarity of the btp moiety in both the ground and excited states. The photophysical results for these o-carboranyl compounds definitively reveal that the planarities of the aryl groups appended to the o-carborane decisively affect the efficiency of radiative decay based on ICT involving the o-carborane.

A series of indium complexes with salen ligands bridged by aryl groups such as [Ar-{N CH(C6H2-3-tBu-5-R)}2]In-Me (Ar = 4,5-dimethyl-1,2-phenylene, 1,2-phenylene, and 3,4-naphthylene; R = H, Br, tBu, Me, OMe, NMe2, and NMe3+) were prepared and fully identified by NMR spectroscopy and elemental analysis. All indium complexes are highly stable in air and aqueous solutions. Among these complexes, the structurally characterized complexes [(4,5-dimethylphenylene)bis(3-tert-butyl-5-methylsalicylideneiminato)-κN,N′,O,O']methylindium(III) and [(2,3-naphthanlene)bis(3-tert-butyl-5-methylsalicylideneiminato)-κN,N′,O,O']methylindium(III) have slightly distorted square-pyramidal geometries around the central indium atoms. The UV/Vis absorption and emission spectra of all indium complexes exhibited significant intramolecular charge transfer (ICT) transitions assigned to the aryl salen-centered π-π* transitions, which displayed a gradual bathochromic shift, resulting from the electronic alteration of the substituent at the C5 position of phenoxy ring. Furthermore, the emission bands also gradually red-shifted as the electron-donating effect of bridging aryl groups decreased. In particular, the emission spectra of the indium complexes were observed in the visible region ranging from green (ca. 500 nm) to deep red (ca. 700 nm). The colors were obtained by manipulating the HOMO and LUMO energy levels, which was further supported by both electrochemical data and theoretical calculations.

Salen-based indium triads, [{(3-tBu)2-(5-Mes2B)2-salen}In-Me] (1) and [{(3-tBu)2-(5-Mes2Bphenyl)2-salen}In-Me] (2), bearing triarylborane (TAB) units were prepared and fully characterised by NMR spectroscopy and elemental analysis. The major absorption bands of 1 and 2 appeared in the region centred at 347 nm and 374 nm, respectively, and the intense emission spectra were observed in the sky blue (λem = 491 nm for 1) and bluish-green (λem = 498 nm for 2) regions, respectively. The solvatochromism effects in various organic solvents and computational calculation results strongly suggested that these absorption and emission features are mainly attributed to intramolecular charge transfer (ICT) transitions between the salen ligand moieties and the TAB units. Furthermore, UV-vis and photoluminescence (PL) titration experiments by the addition of fluoride anions demonstrated ratiometric quenching patterns in both the absorption and emission spectra, indicating that binding of the fluoride anion to the boron centres interrupts these ICT transitions in each compound. Interestingly, both triads exhibited a gradual red-shifted response in each emission spectrum upon the addition of the fluoride anions, resulting in a dramatic colour-change to yellow. The computational calculation results of the S1 states revealed that these emission-colour change properties arise from the elevation of HOMO levels, which are mainly localised on the TAB moieties, resulting from the fluoride anion binding to the borane centres.

A novel class of salen-Al/carbazole dyads (D1 and D2) was synthesized and fully identified. The emission spectra of the dyads presented intriguing dual-emission patterns via an intramolecular energy transfer (IET) state in solution. Furthermore, the IET feature of the dyads was clearly observed in the rigid state. Interestingly, the emission efficiency of the dyads was enhanced by the significant IET process from the carbazole group to the salen-Al moiety. Particularly, D1 exhibited a nearly three-fold enhanced luminescence efficiency compared to the corresponding mononuclear aluminum complexes (A1). Such an emission process of these guest-host systems was further supported by theoretical calculation.

1,3,5-Tris-(o-carboranyl-methyl)benzene (closo-1) and its nido-form (nido-1) were synthesized and fully characterized. The solid-state molecular structure of closo-1 was determined by single-crystal X-ray diffraction analysis. Compound closo-1 exhibited an intense single emission in various organic solvents that was red-shifted with increasing solvent polarity. The positive solvatochromic effect and theoretical calculation results at the first excited (S1) optimized structure of closo-1 strongly suggest that this emissive band can be assigned to an intramolecular charge transfer. Meanwhile, nido-1 showed a pronounced red-shift of the emissive band compared to that of closo-1 and aroused low-energy emission. The specific emissive features of nido-1 were attributed to the elevation of its HOMO level, estimated by cyclic voltammetry. The photophysical changes by conversion from closo-1 to nido-1 allowed the emissive color-tunable sensing of fluoride. Thus, the tris-o-carboranyl compound showed great potential as a chemodosimeter for fluoride anion sensing, detectable by the naked-eye.

Multiple o-carborane substituted compounds, mono-, 1,3-bis-, and 1,3,5-tris[2-(4-butylphenyl)-o-carboran-1-yl]benzene (1–3), were prepared and characterized by multinuclear NMR spectroscopy and elemental analysis. The solid-state structures of 2 and 3 were also confirmed by single-crystal X-ray diffraction. While the mono-carborane compound 1 was nonemissive in the solution state at 298 K, the photoluminescence (PL) spectra of 2 and 3 exhibited weak-to-moderate emission (λem = 352 nm for 2 and 363 nm for 3 in THF). Compounds 2 and 3 showed intriguing dual emission bands (λem = 361 and 537 nm for 2 and λem = 387 and 520 nm for 3) at 77 K, and in film, of which the low-energy band was dominant in the solid state. TD-DFT calculations on the S1 optimized structures suggested that the low-energy fluorescence of 2 and 3 was attributed to the π(4-butylphenyl) → π*(phenylene-o-carborane) intramolecular charge-transfer transition. The low-energy electronic transition of 2 and 3 was apparently associated with aggregation-induced emission, and an enhanced emission intensity (λem = ca. 570 nm for 2 and λem = ca. 550 nm for 3) was observed upon increasing the water fraction (fw) in THF/water mixtures. Furthermore, the PL spectroscopic experiments of poly(3-hexylthiophene-2,5-diyl) (P3HT) polymer films doped with 3 revealed the excellent electron-accepting properties of 3.

Four biphenyl- and fluorene-based o-carboranyl compounds, 4-[2-(p-n-butylphenyl)-1-o-carboran-1-yl]biphenyl (1B), 4,4″-bis[2-(p-n-butylphenyl)-1-o-carboran-1-yl]biphenyl (2B), 2-[2-(p-n-butylphenyl)-1-o-carboran-1-yl]fluorene (1F), and 2,7-bis[2-(p-n-butylphenyl)-1-o-carboran-1-yl]fluorene (2F), were prepared and fully characterized by multinuclear NMR spectroscopy and elemental analysis. The crystal structures of 1B and 2B, analyzed by single-crystal X-ray diffraction, exhibited distinct distortions of the central biphenyl rings with dihedral angles of 44.2 and 33.1°. In photoluminescence measurements, fluorene-based carboranyl compounds in the rigid state (e.g., in solution at 77 K and as films) exhibited a noticeable emission in the low-energy region below 400 nm. 1F displayed a low-energy emissive trace in solution at ambient temperature, whereas biphenyl-based carboranes mainly exhibited high-energy emissions above 400 nm. TD-DFT calculations on the first excited singlet (S1) state of each compound s...

Novel carbazole-conjugated salen-In complexes (Cz1 and Cz2) were prepared and fully characterized by 1H and 13C NMR spectroscopy, elemental analysis, and high-resolution mass spectrometry. The major low-energy absorption bands at λabs = 342 nm for Cz1 and 391 nm for Cz2, respectively, are assigned to typical intramolecular charge transfer (ICT) transitions between the carbazole unit and the salen-In center. The solvatochromism effects in various organic solvents and their large Stokes shift distinctly supported the ICT nature. The photoluminescent spectra of Cz1 and Cz2 showed broad emission bands are centered at 459 nm (blue, λex = 354 nm) and 507 nm (green, λex = 396 nm) in THF, respectively, which are typical feature of CT transitions. In particular, Cz1 showed 8-fold enhanced quantum efficiency relative to that of Cz2, at least 10-fold higher than those of the carbazole-free salen-In complexes. Such enhanced luminescence efficiency of Cz1 originated from efficient radiative decay based on the ICT transition between the salen-In moieties and carbazole parts, as well as its structural rigidity in conversion process between the ground (S0) and excited (S1) states. In other words, Cz2 exhibited low quantum yield due to its structural fluctuation, which is free rotation of both the appended carbazole moieties and bridged phenylene rings in conversion between the S0 and S1 structures. Theoretical calculations clearly supported these intriguing results. In addition, these salen-In complexes exhibited high thermal stability (Td5 = 367 °C for Cz1 and 406 °C for Cz2) and electrochemical stability.

The series of novel salen-based indium complexes (3-tBu-5-R-salen)In-Me (3-tBu-5-R-salen = N,N'-bis(2-oxy-3-tert-butyl-5-R-salicylidene)-1,2-diaminoethane, R = H (1), tBu (2), Br (3), Ph (4), OMe (5), NMe2 (6)) and [(3-tBu-5-NMe3-salen)In-Me](OTf)2 (7; OTf = CF3SO3-) have been synthesized and fully characterized by NMR spectroscopy and elemental analysis. All indium complexes 1-7 are highly stable in air and even aqueous solutions. The solid-state structures for 3-5, which were confirmed by single-crystal X-ray analysis, exhibit square-pyramidal geometries around the indium center. Both the UV/vis absorption and PL spectra of 1-7 exhibit significant intramolecular charge transfer (ICT) transitions based on the salen moieties with systematically bathochromic shifts, which depend on the introduction of various kinds of substituents. Consequently, the emission spectra of these complexes cover almost the entire visible region (λem = 455-622 nm).

Phenanthroimidazole-based triarylborane compounds with an N-phenyl (1Ph, 2Ph) or N-biphenyl (1BP, 2BP) bridge were synthesized and characterized. All four compounds exhibit a dual emission pattern in their photoluminescence (PL) spectra, which can be separated into high- (λem = ca. 380 nm in THF) and low-energy (λem = ca. 480 nm) emissions. While the high-energy emission remains largely unchanged in different organic solvents, the low-energy emission exhibits clear signs of positive solvatochromism. The results of the photophysical analysis and theoretical calculations suggest that the high-energy emission corresponds to a π–π* transition band arising from the phenanthroimidazole, whereas the low-energy emission originates from an intramolecular charge transfer (ICT) transition between phenanthroimidazole and the triarylborane moiety. UV-vis titration experiments examining the association of 1Ph, 2Ph, 1BP, and 2BP with fluoride demonstrate that these compounds associate with a 1:1 binding stoichiometry in THF and binding constants (Ka) that are estimated to be around 1.0–3.0 × 104 M−1. These compounds show a ratiometrically increased fluorescence response in PL titration experiments upon binding of fluoride to the borane moiety, thereby giving rise to a ‘turn-on’ chemosensor for detection of fluoride anions. The ‘turn-on’ properties can be judged as a result of the reinforcement of π–π* transition on phenanthroimidazole and the restriction of ICT transition to triarylborane.

Herein, p-terphenyl-based o-carboranyl compounds, 4,4″-bis[2-(p-n-butylphenyl)-1-o-carboran-1-yl]-p-terphenyl (1) and 4,4″-bis(2-n-butyl-1-o-carboran-1-yl)-p-terphenyl (2), were prepared and fully characterized by multinuclear NMR spectroscopy and elemental analysis. The molecular structure of 1 was also analyzed by single-crystal X-ray diffraction method. Both compounds showed a dual emission band (λem ∼ 350 and 450 nm) in the rigid state (e.g., solution at 77 K), in contrast with a single emission peak at ca. 350 nm observed in solution at ambient temperature. Theoretical calculations on the first excited singlet state of each compound suggested that emission in the low-energy region distinctly involved intramolecular charge transfer (ICT) between carborane and terphenylene rings of both compounds; however, the high-energy emission of 1 was correlated with ICT between carborane and terminal phenyl rings, while that of 2 involved ICT between carborane and terphenylene as well as a π → π∗ transition of the terphenylene moiety. Thus, it was concluded that the absence of terminal phenyl rings in o-carboranyl compounds leads to a π → π∗ transition-based emissive band. The quantum efficiency and radiative decay values of 2, which are not drastically enhanced in the rigid state compared to the solution state at ambient temperature, also showed that the emission band of 2 is not perfectly correlated with the charge transfer (CT) transition band, in contrast to the case of 1.

Potential of mean force (PMF) profiles and position-dependent diffusion coefficients of Na+ and K+ are calculated to elucidate the translocation of ions through a cyclic peptide nanotube, composed of 8 × cyclo[-(d-Leu-Trp)4-] rings, in water and in hydrated DMPC bilayers. The PMF profiles and PMF decomposition analysis for the monovalent cations show that favorable interactions of the cations with the CPN as well as the lipid bilayer and dehydration free energy penalties are two major competing factors which determine the free energy surface for ion transport through CPNs both in water and in lipid bilayers, and that the selectivity of CPNs to cations mainly arises from favorable interaction energies of cations with CPNs and lipid bilayers that are more dominant than the dehydration penalties. Calculations of the position-dependent diffusion coefficients and dynamic friction kernels of the cations indicate that the dehydration process along with the molecular rearrangements occurring outside the channel a...

A dimeric o-carboranyl triarylborane compound (2) with a biphenylene bridge group was prepared and characterized. Also, its solid-state structure was determined via X-ray diffraction. Treatment of 2 with an excess amount of KF in the presence of 18-crown-6 formed a dimer-type potassium salt, [2·F2][K·18-crown-6]2; its structure was fully confirmed by multinuclear NMR spectroscopy. UV–vis titration experiments carried out in THF showed that 2 binds fluoride ions with a binding constant (K) of 8.5 × 105 M–1. The linear decline of the UV/vis absorption of 2 upon titration with fluoride suggested that the triarylborane moieties acted as independent binding sites, which were not affected by each other. Contrary to a single emission (λem = 376 nm) of 2 assignable to an intramolecular charge transfer (ICT) transition at 298 K in THF, a broad low-energy emission band was additionally observed at 77 K, which is dominant in the film state. The TD-DFT calculation on the first excited singlet state (S1) of 2 shows th...

Homoleptic BAr3 (1) and heteroleptic Ar2BAr’ (2) (Ar=4-OMe-2,6-Me2-C6H2-, Ar′=3-Br-6-OMe-2,4-Me2-C6H-) have been selectively synthesized by the reaction between 4-bromo-3,5-dimethylanisole and BF3⋅OEt2 in the presence of n-BuLi. The selectivity of 1 and 2 was controlled by the sequential or in-situ reaction, respectively. The use of stronger base such as t-BuLi than n-BuLi gave only homoleptic 1 even in in-situ reaction. The solid state structure for 2 was confirmed by single crystal X-ray analysis. Especially, the emission of compound 2 showed a bathochromic shift of ca. 50 nm compared with that of compound 1. Both 1 and 2 exhibited significant solvatochromism of fluorescence.