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Photocatalytic molecular conversions that lead to value-added chemicals are of considerable interest. To achieve highly efficient photocatalytic reactions, it is equally important as it is challenging to construct systems that enable effective charge separation. Here, we demonstrate that the rational construction of a biphasic solution system with a ferrocenium/ferrocene (Fc

A self-assembled chemosensor prepared using off-the-shelf materials has shown various fluorescence responses including ratiometric and simple ON-OFF switching profiles by adding different toxic metal ions. The unique fingerprint-like responses have...

A series of novel monocyclometalated [Ir(tpy)(btp)Cl]+ complexes (Ir2-Ir5) were synthesized using 2,2':6',2″-terpyridine (tpy) and 2-(2-pyridyl)benzo[b]thiophene (btp) ligands, as well as their derivatives bearing electron-donating tert-butyl (t-Bu) and electron-withdrawing trifluoromethyl (CF3) groups. Ir2-Ir5 exhibited visible-light absorption stronger than that of the known complex [Ir(tpy)(ppy)Cl]+ (Ir1; ppy = 2-phenylpyridine). Spectroscopic and computational studies revealed that two triplet states were involved in the excited-state dynamics. One is a weakly emissive and short-lived ligand to ligand charge-transfer (LLCT) state originating from the charge transfer from the btp to the tpy ligand. The other is a highly emissive and long-lived ligand-centered (LC) state localized on the btp ligand. Interestingly, the excited state dominant with 3LLCT was completely changed to the 3LC state upon the introduction of substituents on both the tpy and btp ligands. For instance, the excited state of the parent complex Ir2 was weakly emissive (Φ = 2%) and short-lived (τ = 110 ns) in CH2Cl2; conversely, Ir5, fully furnished with t-Bu and CF3 groups, displayed intense phosphorescence with a prolonged lifetime (τ = 14 μs). This difference became increasingly prominent when the solvent was changed to aqueous CH3CN, most probably due to the 3LLCT stabilization. The predominant excited-state nature was switchable between the 3LLCT and 3LC states depending on the substituents employed; this was demonstrated through investigations of Ir3 and Ir4, bearing either the t-Bu or the CF3 group, where the complexes exhibited properties intermediate between those of Ir2 and Ir5. All of the Ir(III) complexes were tested as photosensitizers in photocatalytic H2 evolution over a Co molecular catalyst, and Ir5 outperformed the others, including Ir1, due to improvement in the following key properties: visible-light-absorption ability, excited-state lifetime, and reductive power of the one-electron-reduced species against the catalyst.

We herein propose an easy-to-prepare mini-chemosensor array constructed by two-types of off-the-shelf coumarin dyes for simultaneous classification and quantification of sulfur-containing amino acids (SCAAs) (i.e., l-cysteine, l-cystine, l-homocysteine, glutathione, and glutathione disulfide). The detection mechanism of SCAAs relied on a coordination-based sensor array (CBSA) utilizing the competitive binding among the coumarin dye, a Zn

An artificial tongue that detects astringent components for a comprehensive evaluation of taste has not been established to date. Herein, we first propose fluorescent polythiophene (PT) derivatives (S1-S3) modified with 3-pyridinium boronic acid as supramolecular chemosensors for wine components including astringent procyanidin C1. After numerous attempts for the synthetic conditions, more than 95 mol % of the PT unit was modified with the pyridinium boronic acid moiety. To evaluate the PT derivatives as chemosensors of the artificial tongue, qualitative and quantitative analyses were performed with four types of wine components (i.e., sweet, sour, bitter, and astringent tastes) in combination with pattern recognition models. Notably, procyanidin C1 in the actual wine sample was successfully detected in a quantitative manner. In other words, we have established an authentic artificial tongue using PT based supramolecular chemosensors.

The current work proposes a novel determination method for enantiomeric excess (ee) in (mono- and di-) amines using molecular self-assembly. A pyridine-attached binaphthyl derivative ((R)-1) exhibits fluorescence responses based on imine formation between the aldehyde group of (R)-1 and target chiral amines (i.e. cyclohexane diamine (CHDA), 2-amino-1,2-diphenylethanol (ADPE), 1,2-diphenylethylenediamine (DPDA), 1-amino-2-indanol (AID), and leucinol) in the presence of zinc(II) ions (Zn2+). Because of the multi-optical responses which are derived from the variation of chiral complexes, pattern recognition-based discrimination (i.e. linear discriminant analysis (LDA)) has been achieved for five types of enantiomeric pairs of amines. Possessing such a discrimination capability in combination with data processing (LDA and an artificial neural network) allows accurate determination (prediction error < 1.8%) of the % ee of individual targets such as CHDA which is one of the main components of pharmaceutical drugs. The simple molecular self-assembled system enabled simultaneous multi-chiral discrimination and % ee determination of unknown samples.

We believe that "the simpler we are, the more complete we become" is a key concept of chemical sensing systems. In this work, a "turn-on" fluorescence chemosensor array relying on only two self-assembled molecular chemosensors with ability of both qualitative and quantitative detection of phosphorylated saccharides has been developed. The easy-to-prepare chemosensor array was fabricated by in situ mixing of off-the-shelf reagents (esculetin, 4-methylesculetin, and 3-nitrophenylboronic acid). The fluorescence-based saccharide sensing system was carried out using indicator displacement assay accompanied by photoinduced electron transfer (PeT) under various pH conditions. The simultaneous recognition of 14 types of saccharides including glucose-6-phosphate (G6P) and fructose-6-phosphate (F6P) was achieved with a successful classification rate of 100%. We also succeeded in the quantitative analysis of a mixture of glucose (Glc), as an original substrate, G6P and F6P, as enzymatic products in pseudoglycolysis pathway. Finally, levels of Glc and F6P in human induced pluripotent stem (hiPS) cells were indirectly monitored by using our proposed chemosensor array. Glc and F6P in supernatants of hiPS cells were classified by linear discriminant analysis as a pattern recognition model and the observed clusters represent the activity of hiPS cells. The results show the high accuracy of the proposed chemosensor array in detection of phosphorylated and similarly modified saccharides.

This work reports the design of a highly sensitive solid-state sensor device based on a water-gated organic thin-film transistor (WG-OTFT) for the selective detection of herbicide glyphosate (GlyP) in water. A competitive assay among carboxylate-functionalized polythiophene, Cu2+ , and GlyP was employed as a sensing mechanism. Molecular recognition phenomena and electrical double layer (EDL) (at the polymer/water interface) originated from the field-effect worked cooperatively to amplify the sensitivity for GlyP. The limit of detection of WG-OTFT (0.26 ppm) was lower than that of a fluorescence sensor chip (0.95 ppm) which is the conventional sensing method. In contrast to the previously reported insulated molecular wires to block interchain interactions, molecular aggregates under the field-effect has shown to be effective for amplification of sensitivity through "intra"- and "inter"-molecular wire effects. The opposite strategy in this study could pave the way for fully utilizing the sensing properties of polymer-based solid-state sensor devices.

Due to the photobiology of the flavoproteins DNA photolyase and cryptochrome, electron transfer reactions between flavins and tryptophan are of significant biological relevance. In addition, electr...

Visible light promoted reduction reactions of organohalides, sulfonamides, organonitriles and epoxy ketones were performed using 1,3-dimethylbenzimidazolines possessing 2-hydroxynaphthyl or 2-hydroxyphenyl substituents (HOAr-DMBIH) as photo-reductants. Xe or Hg–Xe lamp through an appropriate glass-filter (λ>390 nm) and a household white light-emitting diode were used as light sources. In these reactions, reductive cleavages of carbon halogen, nitrogen sulfur, carbon carbon (nitrile) and carbon oxygen bonds take place. Bases exert significant effects on the progress of these reactions in a manner that depends on the nature of the substrate. Addition of 1,8-diazabicyclo[5.4.0]undec-7-ene as well as potassium t -butoxide significantly accelerates photo-reduction reactions of organohalides, sulfonamides and organonitriles while the decomposition of formed hydroxy ketones occurs in reactions of epoxy ketones. Single electron transfer from the photo-excited states of benzimidazolines (HOAr-DMBIH) or their deprotonated analogues ( − OAr-DMBIH) to the substrates is proposed to initiate these reactions.

Recently, the photochemistry of cationic bis-cyclometalated Ir(III) complexes has gained increasing attention in interdisciplinary studies owing to the characteristic photofunctions of the complexes, including long-lived and strong phosphorescence, visible-light absorption, and photosensitizing properties. Herein, two Ir(III) complexes, Ir2 and Ir3, composed of coumarin 6 and different ancillary ligands (i.e., 4,4′-dimethyl-2,2′-bipyridine and 2-(2-pyrazolyl)pyridine) were prepared and characterized to investigate their photophysical properties in several solvents. These compounds were incorporated into DPPC vesicles to investigate their photosensitizing properties in an aqueous solution. Ir2 and Ir3 absorbed light strongly in the visible region and exhibited similar phosphorescence spectral profiles dominated by the coumarin ligands in all tested environments. In contrast, the ancillary ligands and the surrounding environment influenced the excited-state deactivation pathways. For instance, the phosphorescence of Ir2 was weak in highly polar solvents and the vesicle membrane, and in contrast, Ir3 exhibited intense and surprisingly long-lived phosphorescence in these media (Φ = 25–38% and τ = 32–41 μs). Visible-light illumination of Ir2 and Ir3 bound to the membrane surface resulted in H2 evolution when an electron donor and a water-soluble Ni(II) catalyst were present in the outer aqueous phase. Under these conditions, the reaction system incorporating Ir2 performed much better than the Ir3 system in terms of photosensitizer stability and turnover frequency.

Vesicles, approximately spherical bilayer membranes formed by self-organization of phospholipids, have been employed as reaction fields to construct artificial systems capable of converting light energy into chemical potential. To gain information about the performance of water oxidation catalysts in vesicular membranes, the complex [Ru(bda)(pyCO 2 Ocd)(pyCO 2 Me)] (H 2 bda = 2,2′-bipyridine-6,6′-dicarboxylic acid, pyR = pyridine having a substituent R at the 4-position, Ocd = (CH 2 ) 17 CH 3 ) was newly synthesized, and photochemical water oxidation using the complex embedded into vesicle membranes as a catalyst was investigated in an aqueous solution containing a sensitizer [Ru(bpy) 3 ] 2+ (bpy = 2,2′-bipyridine) and a sacrificial electron acceptor S 2 O 8 2− . At first, the dependence of the initial rate of O 2 production, v i , on the concentration of [Ru(bpy) 3 ] 2+ , as well as S 2 O 8 2− , was investigated to find optimum conditions to examine the performance of the catalyst. Subsequently, the dependence of v i on the catalyst concentration was examined in the vesicular system, indicating that v i increased approximately linearly with the catalyst concentration up to ∼30 μM, and declined after that. The turnover frequency for O 2 production with respect to the catalyst was evaluated to be 39.1 h −1 , which was larger than that in similar systems in a homogeneous solution by a factor of more than two. The reason for the linear dependence of v i on the catalyst concentration, as well as the superior performance of the catalyst in the vesicular system, was discussed on the basis of the mechanism accepted generally for the water oxidation catalyzed by related Ru complexes.

Benzimidazolium naphthoxide (-ONap-BI+) was first synthesized and utilized as an unprecedented betaine photoredox catalyst. Photoexcited state of -ONap-BI+ generated by visible light irradiation catalyzes the reductive deiodination as well as desulfonylation reactions in which 1,3-dimethyl-2-phenylbenzimidazoline (Ph-BIH) cooperates with as an electron and hydrogen atom donor. Significant solvent effects on the reaction progress were discovered, and specific solvation toward imidazolium and naphthoxide moieties of -ONap-BI+ was proposed.

A series of monomeric RuII complexes [Ru(bda)(pyR)2] (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid, pyR = pyridine with a substituent R at the 4-position) were prepared, and the effects of substituent groups on the pyridine ligands of the complexes on catalytic activities toward water oxidation, as well as on photophysical and electrochemical properties, were examined. An increase in the electron-withdrawing ability of the substituent results in a redshift of the absorption maximum assigned to the transition from the d orbital of Ru to the π* orbitals of the pyridine ligands, and an increase in the oxidation potential of the complex. These results are reasonably explained in terms of the variation of the energy level of molecular orbitals induced by the substituent group, which is supported by density functional theory calculations. The substituent effect on catalytic activity toward photochemical water oxidation using [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) and S2O82– as a sensitizer and a sacrificial electron acceptor, respectively, is essentially analogous to that toward chemical water oxidation using CeIV as an oxidant in which the complexes with electron-withdrawing groups exhibit better performance than those with electron-donating groups. However, the Hammett analysis demonstrates that the catalytic activities of the complexes toward chemical and photochemical water oxidation show no straightforward dependence on the electronic nature of the substituent group, which suggests that a step accelerated by electron-donating groups also contributes to the overall rate of water oxidation.

Photoinduced electron transfer (PET) reactions promoted by 2-aryl substituted 1,3-dimethylbenzimidazolines (Ar-DMBIH) were investigated. Excited states of Ar-DMBIH, formed by irradiation using light above 360 nm, initiate PET reductions of various organic substrates, including transformations of epoxy ketones to aldols, free radical rearrangements such as the Dowd-Beckwith ring-expansion and 5- exo hexenyl cyclization, deprotection of N -sulfonyl-indols, and allylation of acyl formates. In these processes, Ar-DMBIH possessing 1-naphthyl, 2-naphthyl, 1-pyrenyl and 9-anthryl substituents formally act as two electron and one proton donors while the hydroxynaphthyl substituted derivative serves as a two electron and two proton donor. On the basis of the results of absorption spectroscopy studies, cyclic voltammetry and DFT calculation, a mechanistic sequence for these reduction reactions is proposed that involves initial photoexcitation of the aryl chromophore of the Ar-DMBIH followed by single electron transfer (SET) to the organic substrate to generate the radical cation of benzimidazoline and the radical anion of the substrate.

A combination of 2-aryl substituted 1,3-dimethyl-benzimidazolines (DMBIHs) and tris(2,2′-bipyridine)ruthenium(II) chloride, Ru(bpy)3Cl2 was used to promote photoinduced electron-transfer (PET) reactions of α-halomethyl-substituted benzocyclic 1-alkanones. This photo-reagent system stimulates free radical forming, cleavage of both carbon–bromine and carbon–chlorine bonds that are not activated by carbonyl groups. The resulting free radicals undergo 5-exo hexenyl cyclization as well as sequential cyclization and ring-expansion (Dowd–Beckwith) reactions to form radicals that abstract hydrogen atoms from the radical cation of DMBIH to yield the observed products. The results of a study of the effects of substituents located on the 2-aryl ring of DMBIH suggest that steric and hydrogen-bonding interactions influence the nature of the reaction pathways followed by the radical intermediates. PET reactions using an iridium complex and DMBIH were also investigated.

We report a novel system of visible-light-driven CO2 reduction to CO in an aqueous solution, in which DPPC vesicles dispersed in the solution act as a photocatalyst using ascorbate (HAsc(-)) as an electron source. In the vesicles metal complexes [Ru(dtb)(bpy)2](2+) and Re(dtb)(CO)3Cl (dtb = 4,4'-ditridecyl-2,2'-bipyridyl) are incorporated, which act as a photosensitizer and a catalyst for CO2 reduction, respectively. The reaction is initiated with the reductive quenching of the (3)MLCT excited state of the Ru complex with HAsc(-), followed by an electron transfer from the reduced Ru complex to the Re complex to give a one-electron reduced Re species having catalytic ability for CO2 reduction. In order to search for optimum conditions for the CO production, the dependence of the initial rate of CO formation, vi, on the concentration of the metal complexes and HAsc(-) in the vesicle solution was examined. Consequently, we obtained ∼3.5 μmol h(-1) and 190 for vi and the turnover number for CO formation with respect to the Re catalyst, respectively. On the basis of the dependence of vi on the incident light intensity, we have concluded that the photocatalytic reduction of CO2 to CO with HAsc(-) in this system requires only one photon, and propose that HAsc(-) donates an electron not only to the excited state of the Ru complex, but also to the Re-CO2 adduct involved in the catalytic cycle for CO2 reduction.

A bichromophoric cationic iridium complex having a pyrene-substituted bipyridine ligand acts as a sensitizer for visible-light-driven electron transport from ascorbate (an electron donor) to methyl...

A series of bis-cyclometalated cationic iridium (Ir) complexes were synthesized employing two coumarin 6 ligands and a 2,2'-bipyridine (bpy) with various substituents as new sensitizers, realizing both features of strong visible-light absorption and long-lived excited state. Complexes 2-4, with electron-donating methyl and methoxy groups, absorbed visible light strongly (ε: 126 000-132 000 M(-1) cm(-1)) and exhibited room-temperature phosphorescence with remarkably long lifetimes (21-23 μs) in dichloromethane. In contrast, the excited state of prototype complex 1 without any substituents was short-lived, particularly in highly polar acetonitrile. Phosphorescence of complex 5 with the strong electron-withdrawing CF3 groups was too weak to be detected at room temperature even in less polar dichloromethane. The triplet energies of their coumarin ligand-centered ((3)LC) phosphorescent states were almost invariable, demonstrating that selective tuning of the excited-state lifetime is possible through this "simple chemical modification of the bpy ligand" (we name it the "SCMB" method). The spectroscopic and computational investigations in this study suggest that a potential source of the nonradiative deactivation is a triplet ligand-to-ligand charge-transfer state ((3)LLCT state, coumarin 6 → bpy) and lead us to conclude that the energy level of this dark (3)LLCT state, as well as its thermal population, is largely dependent on the substituents and solvent polarity. In addition, the significant difference in excited-state lifetime was reflected in the photosensitizing ability of complexes 1-5 in visible-light-driven hydrogen generation using sodium ascorbate and a cobalt(III) diglyoxime complex as an electron donor and a water-reduction catalyst, respectively. This study suggests that the SCMB method should be generally effective in controlling the excited state of other bis-cyclometalated cationic Ir(III) complexes.

Cationic iridium(III) complexes comprising two cyclometalating 3-(2-benzothiazolyl)-7-(diethylamino)coumarin (Coumarin 6) ligands and one diimine ancillary ligand (N N) were prepared [N N = 2,2′-bipyridyl (2), 1,10-phenanthroline (3), 2,2′-biquinoline (4)] and examined for their photophysical properties. The synergic effect of the intraligand charge-transfer (ILCT) transition in the chromophoric Coumarin 6 moiety and the metal-ligand-to-ligand CT (MLLCT) and/or ligand-to-ligand CT (LLCT) transitions associated with the diimine ligand rendered these complexes strongly absorptive in the visible region. Their enhanced absorptivity is significant when compared to the corresponding electroneutral complex 1 with acetylacetonate. Specifically, the molar extinction coefficient of complex 2 reached 129000 M–1 cm–1 at 483 nm, which is an unprecedentedly high value relative to those of other recently reported Ir-based dyes. Ir sensitizers 2–4 were tested for visible-light-driven hydrogen generation by using an Ir–Co photocatalytic system, where triethylamine and tris(2,2′-bipyridyl)dichloridocobalt were employed as a sacrificial electron donor and a water-reduction catalyst, respectively. As a result, complexes 2 and 3 were found to be highly effective sensitizers displaying turnover numbers up to 1500.

Photoinduced electron-transfer reaction of α-bromomethyl-substituted benzocyclic β-keto esters with tertiary amines was investigated. Debrominated β-keto esters and ring-expanded γ-keto esters were obtained as major products. On the basis of mechanistic experiments it was concluded that these products are formed via a reaction sequence of selective carbon–bromine bond cleavage and subsequent competitive hydrogen abstraction and Dowd–Beckwith ring-expansion of the resulting primary alkyl radicals. The characteristic product distribution observed for the type of amine used is rationalized on the basis of selective reaction pathways of generated radical intermediates that depend on the nature of the amine radical cations.

Combinations of electron-withdrawing and -donating substituents on the 8-hydroxyquinoline ligand of the tris(8-hydroxyquinoline)aluminum (Alq(3)) complexes allow for control of the HOMO and LUMO energies and the HOMO-LUMO gap responsible for emission from the complexes. Here, we present a systematic study on tuning the emission and electroluminescence (EL) from Alq(3) complexes from the green to blue region. In this study, we explored the combination of electron-donating substituents on C4 and C6. Compounds 1-6 displayed the emission tuning between 478 and 526 nm, and fluorescence quantum yield between 0.15 and 0.57. The compounds 2-6 were used as emitters and hosts in organic light-emitting diodes (OLEDs). The highest OLED external quantum efficiency (EQE) observed was 4.6%, which is among the highest observed for Alq(3) complexes. Also, the compounds 3-5 were used as hosts for red phosphorescent dopants to obtain white light-emitting diodes (WOLED). The WOLEDs displayed high efficiency (EQE up to 19%) and high white color purity (color rendering index (CRI≈85).

Pyrene-sensitized transmembrane electron transport from ascorbate (Asc−) in the inner waterpool to methylviologen (MV2+) in the outer aqueous solution proceeded in gel-phase DPPC vesicles, in which the lateral diffusion of molecules embedded in the vesicle bilayers is totally restricted. Based on the effects of the sensitizer concentration and cholesterol added to DPPC membranes on the efficiency of the electron transport, we propose that the sensitizer clusters play an essential role in the electron transport in DPPC vesicles. The presence of the sensitizer clusters in DPPC vesicles is supported by the temperature dependence of the intensity ratio of the excimer to the monomer fluorescence of the sensitizer. We found that this photoinduced transmembrane electron transport system works using various electron donors that undergo a reversible redox cycle other than Asc−, and that there is a tendency for electron donors having lower oxidation potential to give a larger rate of MV+ formation. Moreover, we accomplished the connection of the system of the photoinduced transmembrane electron transport in DPPC vesicles with the system for hydrogen generation from water using colloidal platinum as a catalyst.

The efficiency improvement of fluorescent organic light-emitting diodes (OLEDs) is achieved by tuning the work function of a hole-injection layer (HIL) of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). This tuning is achieved by treating PEDOT:PSS with ultraviolet light (UV)–ozone plasma exposure. In order to demonstrate the effect of the UV–ozone treatment, two simple green-emitting device OLED architectures were used; Device I utilized tris(8-quinolinolato) aluminum (Alq 3 ) as an emitter while Device II employed Alq 3 doped with 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)quinolizino[9,9a,1gh]-coumarin (C545T) emissive layer. The study showed that the OLEDs efficiency depends on the type of device configuration and the duration of the UV–ozone exposure. Here, a short time exposure of UV–ozone treatment of 4 min and 8 min was found optimal for the best device characteristics. The maximum power efficiency in Device I increased from 1.05 lm/W (untreated) to 2.70 lm/W, while Device II, doped with emitter increased from 4.10 lm/W to 8.24 lm/W. Consequently, Device I and Device II obtained the 100% increase in the power efficiency. The improvements in device efficiency is attributed to the efficient injection and balance in charge carriers resulting from the tuned work function of the PEDOT:PSS.

Two new bipolar host materials based on a 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) core with the carbazole and diphenylamine groups were designed, synthesized, and applied in phosphorescent organic light-emitting diodes (PhOLEDs). The DFT calculations indicated desirable distribution of HOMO and LUMO densities, suggesting potential for bipolar charge transport. In addition, the electrochemical and phosphorescence studies revealed that neither the LUMO level nor the triplet energies differ significantly from the parent TPBI suggesting that the new materials would be suitable as hosts capable of both electron and hole transport and suitable for harvesting green electrophosphorescence. As a result of broader charge recombination zone resulting from the bipolar properties of new hosts, the devices with a simple architecture achieved significantly better current efficiencies of 48 and 60 cd/A (the power efficiencies of 46 and 70 lm/W), compared with a device using conventional TPBI host (19 cd/A; 21...

Tris(trimethylsilyl)silane (TTMSS) promoted free radical reaction in benzotrifluoride (BTF) was investigated. Compared to same reaction using environmentally less desirable tri-n-butyltin hydride (TBTH) in benzene, less quantity of BTF than that of benzene can be used because of slower hydrogen atom transfer from TTMSS than that from TBTH toward primary alkyl radicals. Also, electron-transfer reactions promoted by tris(p-bromophenyl)aminium hexachloroantimonate (TBPA) and FeCl3 were conducted in BTF. Then, TBPA was found to be effective in BTF comparably to that in methylene chloride. In addition, an interesting observation that FeCl3 promoted reaction was accelerated by the addition of imidazolium salt was made. All the results suggest that BTF is a tolerable solvent for free radical reaction with TTMSS and electron-transfer reactions using TBPA as well as FeCl3.

A series of new blue-phosphorescent iridium(III) complexes 1-14 with ligands of 2-phenylimidazo[1,2-a]pyridine (pip) derivatives were successfully prepared, and their electrochemical, photophysical, and electroluminescent (EL) properties were systematically investigated. It was found that the emission maxima are significantly dependent on the substituents on the phenyl ring in the range of 489-550 nm. For instance, electron-withdrawing groups such as F and CF3 shift the emission maxima to shorter wavelengths by lowering the HOMO levels (complexes 4-8), whereas the extended pi-conjugation leads to bathochromic shifts (2, 3). To obtain further information about the frontier orbital, substitution effects on the imidazole part were also investigated here, and it was found that electron-withdrawing or -donating substituents on the imidazole ring affected the emission maxima (9, 557 nm; 10, 525 nm). These results including their oxidation potentials suggest that the HOMO of the pip-based complex is a mixture of Ir-d, phenyl-pi, and imidazole-pi orbitals. From this viewpoint, combination of electron-withdrawing substituents on the phenyl ring with the use of another ancillary ligand enabled further blue shifts (13, 468, 499 nm; 14, 464, 494 nm). This new system based on pip is one of the rare examples of iridium complexes whose emissions can be tuned to the blue region. Preliminary polymer light-emitting devices (PLEDs) employing the Ir complexes were fabricated, and the devices showed moderate EL efficiencies.

A series of phosphorescent cyclometalated iridium(III) complexes 4–6 with new ligands of bicyclic phenylvinylpyridines have been synthesized and systematically examined for their photophysical, electrochemical and electroluminescence (EL) properties. All of the bis- and tris-cyclometalated complexes could be characterized by 1H-NMR, elemental analysis and X-ray crystal structure analysis. The phosphorescence colour of the complexes in solution, the solid state and polymer film is unusually changed depending on the structure of the ligand. EL devices using the complexes exhibited external quantum efficiencies (EQE) of 1.2–8.1% at 100 cd m−2, and EL colour tuning in the range of 571–635 nm was achieved analogous to PL properties of the phosphors. X-Ray analyses of complexes 4a–c demonstrated that the degree of steric hindrance increases with an increase of the cycloalkane ring size, leading to hypsochromic shifts of emission by the distortion of the phenyl groups. X-Ray analyses also suggested that long iridium–carbon bonds are unfavorable for efficient electroluminescence. In addition, we have found a unique and important aspect for the study of EL devices: the EL devices based on complexes 4c, 6a show moderate EL efficiencies (EQE = 4.0 and 6.1%) although these complexes have no emission in solution at room temperature, indicating that the PL properties of the complexes in solution are not directly related to the EL efficiencies.

A cationic cyclometallated Ir(III) complex with 1,10-phenanthroline and 2-phenylpyridine ligands photosensitizes the production of singlet oxygen, O2(a(1)Δ(g)), with yields that depend appreciably on the solvent. In water, the quantum yield of photosensitized O2(a(1)Δ(g)) production is small (ϕ(Δ) = 0.036 ± 0.008), whereas in less polar solvents, the quantum yield is much larger (ϕ(Δ) = 0.54 ± 0.05 in octan-1-ol). A solvent effect on ϕ(Δ) of this magnitude is rarely observed and, in this case, is attributed to charge-transfer-mediated processes of non-radiative excited state deactivation that are more pronounced in polar solvents and that kinetically compete with energy transfer to produce O2(a(1)Δ(g)). A key component of this non-radiative deactivation process, electronic-to-vibrational energy transfer, is also manifested in pronounced H2O/D2O isotope effects that indicate appreciable coupling between the Ir(III) complex and water. This Ir(III) complex is readily incorporated into HeLa cells and, upon irradiation, is cytotoxic as a consequence of the O2(a(1)Δ(g)) thus produced. The data reported herein point to a pervasive problem in mechanistic studies of photosensitized O2(a(1)Δ(g))-mediated cell death: care must be exercised when interpreting the effective cytotoxicity of O2(a(1)Δ(g)) photosensitizers whose photophysical properties depend strongly on the local environment. Specifically, the photophysics of the sensitizer in bulk solutions may not accurately reflect its intracellular behavior, and the control and quantification of the O2(a(1)Δ(g)) "dose" can be difficult in vivo.

New iridium complexes with ligands of 2-phenylimidazo[1,2-a]pyridines were prepared, and their emission maxima were found to be greatly dependent on the substituents. A trifluoromethyl group on the imidazole part made the emission maximum blue-shifted, and combination with the same groups on the phenyl ring resulted in the bluest phosphorescence among the derivatives.

Photoinduced electron-transfer reactions of several ketone substrates were studied to evaluate the utilities of 1,6-bis(dimethylamino)pyrene (BDMAP), 1,6-dimethoxypyrene (DMP), 9,10-bis(dimethylamino)anthracene (BDMAA), and 9,10-dimethoxyanthracene (DMA) as electron-donating sensitizers cooperating with 2-aryl-1,3-dimethylbenzimidazolines. BDMAP and DMP generally led higher conversion of ketones and better yield of reduction products compared to BDMAA and DMA.

We constructed a novel H2 generation system mimicking natural photosynthesis, in which an electron is transported photochemically from ascorbate entrapped in the inner waterpool of vesicles to MV2+...

A benzimidazoline ligand in combination with a Ru- or Ir-complex promotes photoinduced electron-transfer reactions of α-halomethyl substituted substrates to form primary alkyl radicals via selective C-halogen bond cleavage.

Bis-cyclometalated cationic iridium (Ir) complexes 1-4 comprising two 2-(2-pyridyl)benzo[b]thiophene (btp) ligands and one 2,2'-bipyridyl (bpy) ancillary ligand with different substituents were prepared as new visible light-absorbing sensitizers and examined for their photophysical and electrochemical properties. Complex 1 was prepared as a parent complex without any substituents. Complexes 2-4 contained methyl-, methoxy-, and trifluoromethyl groups at 4,4'-positions on the bpy ancillary ligand. Systematic investigation of these complexes revealed that such a simple chemical modification selectively controls the excited-state lifetime, while the absorption and emission spectral features remain unchanged. Specifically, the phosphorescence lifetimes of complexes 2 and 3 with electron-donating groups (τ = 3.50 μs, 3.90 μs) were found to be much longer than that of complex 1 (τ = 0.273 μs), and complex 4, possessing strong electron-withdrawing trifluoromethyl groups, did not exhibit detectable phosphorescence at room temperature. The large differences in excited-state lifetimes of complexes 1-3, as well as the nonemissive character of complex 4, are attributed to a strong influence of the substituents on the ligand field strength. The increased σ-donating ability of the ancillary ligand in complexes 2 and 3 destabilizes a short-lived, nonemissive triplet metal-centered ((3)MC) state and increases the energy separation between the (3)MC state and emissive triplet ligand-centered ((3)LC) state based on the btp ligand. For complex 4, however, the (3)MC state is close in energy to the (3)LC state because of the decreased σ-donating ability of the ancillary ligand. Additional evidence of the (3)MC state associated with the changeable excited state was also provided via low-temperature phosphorescence measurements and density functional theory calculations. Ir complexes 1-4 were tested as sensitizers in photoinduced electron-transfer reaction of triethanolamine and methylviologen chloride (MVCl2). As a result, complexes 2 and 3 exhibited much better photosensitizing property compared to complex 1 since their long-lived excited states promoted an oxidative quenching pathway. This Study has first demonstrated that simple substitution on the diimine ancillary ligand can control the (3)MC state of the bis-cyclometalated cationic Ir complex to finely tune the excited-state lifetime and photosensitizing property.

Photooxidation reactions of 1,5-dihydroxynaphthalene (DHN) have been carried out in the presence of cyclometalated neutral and cationic iridium (Ir) complexes 1-6 as singlet oxygen ((1)O(2)) sensitizers in order to investigate the (1)O(2) generation quantum yield and photosensitizing durability of the complexes. The reactions allowed a successful kinetic study to provide the pseudo-first-order rate constants and the initial rates of DHN consumption, which in turn led to the (1)O(2) generation quantum yields. The results revealed that cationic Ir complexes [Ir(ppy)(2)(phen)(+) (4) and Ir(ppy)(2)(bpy)(+) (5), where ppy = 2-phenylpyridine, phen = 1,10-phenanthroline, bpy = 2,2'-bipyridyl] have high (1)O(2) generation quantum yields (Φ(Δ) = 0.93, 0.97). On the other hand, neutral complexes with lower oxidation potentials were considered to have a more efficient charge-transfer (CT) interaction with molecular oxygen, which decreased the efficiency of singlet oxygen formation. Additionally, a steric factor of the ligands was reflected in (1)O(2) generation quantum yield. High yields of the oxidized product for the photoreactions using the cationic complexes indicated their excellent photosensitizing durability, originating from the high photochemical stability upon irradiation.

2-(p-Methoxyphenyl)-1,3-dimethylbenzimidazoline (ADMBI) and 2-(o-hydroxyphenyl)-1,3-dimethylbenzimidazoline (HPDMBI) are used as reducing reagents in 1,8-dimethoxypyrene (1,8-DMP) sensitized, photoinduced electron transfer (PET) reactions. This system was effectively used for PET induced, reductive transformations of various organic substrates, including α,β-epoxy ketones, the olefin tethered 2-bromomethyl-1-tetralone, and o-allyloxy-iodobenzene, as well as for the deprotection reactions of dodecyl-2-benzoylbenzoate and N-sulfonylindole. The results of studies show that 1,8-DMP is a more effective sensitizer than the previously used 9-methylcarbazole for deprotection of N-methyl-4-picolinium ester.

Tris(trimethylsilyl)silane (TTMSS) promoted free radical reaction in benzotrifluoride (BTF) was investigated. Compared to same reaction using environmentally less desirable tri-n-butyltin hydride (TBTH) in benzene, less quantity of BTF than that of benzene can be used because of slower hydrogen atom transfer from TTMSS than that from TBTH toward primary alkyl radicals. Also, electron-transfer reactions promoted by tris(p-bromophenyl)aminium hexachloroantimonate (TBPA) and FeCl3 were conducted in BTF. Then, TBPA was found to be effective in BTF comparably to that in methylene chloride. In addition, an interesting observation that FeCl3 promoted reaction was accelerated by the addition of imidazolium salt was made. All the results suggest that BTF is a tolerable solvent for free radical reaction with TTMSS and electron-transfer reactions using TBPA as well as FeCl3.

2-Aryl-1,3-dimethylbenzimidazolines (DMBIHs) have been applied to photoinduced electron-transfer reductions of various organic substrates. Either direct or indirect electron transfer between the substrates and DMBIHs is utilized to promote the desired transformations. Photoexcitation of the substrates using light above 280 nm was carried out in the former protocol whereas a photosensitization method using materials such as substituted pyrenes, ruthenium and iridium complexes that absorb longer-wavelength light was employed in the latter. In these reactions, DMBIHs undergo initial electron transfer and subsequent proton or hydrogen atom transfer.

Photoinduced electron transfer reaction of 2-bromomethyl-2-(3-butenyl)benzocyclic-1-alkanones with amines afforded 5-exo radical cyclization products while electron transfer reaction with samarium diiodide produced cyclopropanols.

We have developed new blue-phosphorescent iridium complexes based on 2-phenylpyridine derivatives with pertinent substituents and an ancillary ligand to accomplish selective tuning of the HOMO and ...