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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.

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.

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.

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.

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.

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.

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.

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.

Closo-o-carboranyl compounds bearing the ortho-type perfectly distorted or planar terphenyl rings (closo-DT and closo-PT, respectively) and their nido-derivatives (nido-DT and nido-PT, respectively) were synthesized and fully characterized using multinuclear NMR spectroscopy and elemental analysis. Although the emission spectra of both closo-compounds exhibited intriguing emission patterns in solution at 298 and 77 K, in the film state, closo-DT mainly exhibited a &pi, &pi, * local excitation (LE)-based emission in the high-energy region, whereas closo-PT produced an intense emission in the low-energy region corresponding to an intramolecular charge transfer (ICT) transition. In particular, the positive solvatochromic effect of closo-PT and theoretical calculation results at the first excited (S1) optimized structure of both closo-compounds strongly suggest that these dual-emissive bands at the high- and low-energy can be assigned to each &pi, * LE and ICT transition. Interestingly, both the nido-compounds, nido-DT and nido-PT, exhibited the only LE-based emission in solution at 298 K due to the anionic character of the nido-o-carborane cages, which cannot cause the ICT transitions. The specific emissive features of nido-compounds indicate that the emissive color of closo-PT in solution at 298 K is completely different from that of nido-PT. As a result, the deboronation of closo-PT upon exposure to increasing concentrations of fluoride anion exhibits a dramatic ratiometric color change from orange to deep blue via turn-off of the ICT-based emission. Consequently, the color change response of the luminescence by the alternation of the intrinsic electronic transitions via deboronation as well as the structural feature of terphenyl rings indicates the potential of the developed closo-o-carboranyl compounds that exhibit the intense ICT-based emission, as naked-eye-detectable chemodosimeters for fluoride ion sensing.

The design and synthesis of the first asymmetrically “two-walled” meso-substituted calix[4]pyrrole tethered by a fluorophore and its subsequent implication as an archetype sequential ‘on–off–on–off’ fluorescent single-molecular switch are reported. The current system permits us to extend the sensitivity up to sub-nanomolar levels with the detection limit as low as 0.4 nM.

Three novel BODIPY-based heterodinuclear complexes, [salen(3,5-(t)Bu)2Al-(OC6H4-BODIPY)] (6), [salen(3,5-(t)Bu)2Al-(OC6F2H2-BODIPY)] (7), and [(mq)2Al-(OC6H4-BODIPY)] (8) (salen = N,N'-bis(salicylidene)ethylenediamine, BODIPY = 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, and mq = methyl-8-quinolinolato) were prepared and characterized by multinuclear NMR spectroscopy. The specific structures of 6-8 were also determined by single crystal X-ray analysis. In particular, the salen-based heterodinuclear complexes 6 and 7 exhibited higher thermal stability (Td5 = 309 and 306 °C, respectively) than that of the closely related mononuclear aluminum or BODIPY compounds, except for 8. The UV/vis absorption and PL spectra for 6 and 7 indicated a significant photoinduced energy transfer from the aluminum-salen moiety to the BODIPY group in an intramolecular manner. Theoretical calculations revealed independent transition states of the aluminum-salen moiety or the BODIPY group in the Al(III)-BODIPY dyads, further supporting these experimental results.

Novel salen-Al/triarylborane dyad complexes were prepared and characterized with their corresponding mononuclear compounds. The UV–vis and photoluminescence experiments for dyads exhibited photoinduced energy transfer from borane to the salen-Al moiety in an intramolecular manner. Theoretical calculation and fluoride titration results further supported these intramolecular energy-transfer features.

transition by time-dependent density functional theory calculations. Potential energy surfacesof both the ground and electronically excited states were obtained employing quantum chemical calculations.It was suggested that the dissociation of OH from propiolic acid excited at 212 nm should take place along theS

Three dithienosilole (DTS) derivatives bearing naphthyl segments, 5,5′-dinaphthyl-1,1-dimethyldithienosilol (1), 5,5′-dinaphthyl-1-methyl-1-phenyldithienosilole (2), and 5,5′-dinaphthyl-1,1-diphenyldithienosilol (3), are prepared through Pd(II)-catalyzed cross-coupling using an organoindium reagent as a nucleophile. The molecular structure of 3 is confirmed by single-crystal X-ray analysis. In addition, thermal, photophysical, and electrochemical properties for all three compounds are systematically investigated. The introduction of naphthyl segments into the DTS framework leads to an excellent enhancement of thermal stability with relatively high glass transition (Tg: 87 °C) and decomposition temperatures (Td: 320−380 °C). A red shift in both absorption and emission is observed in the DTS series as the 1,1-substituents on the ring silicon atom become more electronegative. On the basis of absorption spectra and DFT/TDDFT calculations, intense green photoluminescence observed for all compounds can be attri...

Photodissociation dynamics of propargyl alcohol (HC identical withC-CH(2)OH) at 212 nm in the gas phase was investigated by measuring rotationally resolved laser-induced fluorescence spectra of OH ((2)Pi) radicals exclusively produced in the ground electronic state. From the spectra, internal energies of OH and translational energy releases to products were determined. The electronic transition at 212 nm responsible for the OH dissociation was assigned as the pi(C[triple bond]C) --> pi*(C[triple bond]C) transition by time-dependent density functional theory calculations. In addition, an energy barrier at the exit channel along the reaction coordinate on the excited electronic potential energy surface was identified by ab initio calculations. The observed energy partitioning among the fragments was successfully modeled by the so-called "barrier-impulsive model".

CN) at 193 nm has been investigated by measuring rotationallyresolved laser induced fluorescence sp ectra of CN fragments, from which rotational population distributions ofCN as well as translational energy releases in the products were obtained. From quantum chemical molecularorbital calculations, a mixture of the n →π

Mixed quantum-classical atomistic simulations have been carried out to investigate the mechanistic details of excited state intramolecular electron transfer in a betaine-30 molecule in acetonitrile. The key electronic degrees of freedom of the solute molecule are treated quantum mechanically using the semiempirical Pariser-Parr-Pople Hamiltonian, including the solvent influence on electronic structure. The intramolecular vibrational modes are also treated explicitly at a quantum level, with the remaining elements treated classically using empirical potentials. The electron-transfer rate, corresponding to S1 --S0 relaxation, is evaluated via time-dependent perturbation theory with the explicit inclusion of the dynamics of solvation and intramolecular conformation. The calculations reveal that, while solvation dynamics is critical to the rate, the intramolecular torsional dynamics also plays an important role. The importance of the use of multiple high-frequency quantum modes is also discussed.

E-mail: hlkim@kangwon.ac.krReceived November 14, 2011, Accepted December 2, 2011Key Words : Formic acid, Photodissociation dynamics, Laser induced fluorescence, H atomsChemistry of formic acid (HCOOH) is of fundamentalinterest because it is an important intermediate in oxidationof unsaturated hydrocarbons in combustion and the mostabundant organic pollutant in Earth's atmosphere. Structuresand dynamics of formic acid in the excited electronic statesare of special importance in understanding atmosphericchemistry. In UV, the absorption spectrum shows somevibrational structures superimposed by continuous absorp-tion starting from about 250 nm, which is assigned as the n→ π

Three new organic dyes that contain the dithienosilole (DTS) moiety as spacer have been synthesized and their photophysical/electrochemical properties, theoretical calculation and dye-sensitized solar cell (DSSC) performance have been investigated. The overall conversion efficiencies for DSSCs based on these dyes range from 6.73 to 7.50%, comparable to a (3–5′-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]2,2′-bithiophene-5-yl}-2-cyanoacrylic acid (JK-2)-sensitized device (7.63%), fabricated and measured under the same experimental conditions. The DSSC constructed from one of the three compounds shows a higher open-circuit voltage (VOC) compared to those of the other two dye sensitized solar cells due to an increased electron lifetime (τe) in the conduction band of TiO2.

Department of Chemistry, Konkuk University, Seoul 143-701, KoreaReceived August 28, 2011, Accepted November 2, 2011Key Words : Dye-Sensitized Solar Cells (DSSCs), Bulky spacer, Photon to current conversion efficiencyRuthenium dye-based dye-sensitized solar cells (DSSCs)have received great deal of attraction from chemists andmaterial scientists because of their over 10% of photon tocurrent conversion efficiency.