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A novel organic small molecule bis-triphenylamine with spiro(fluorene-9,9′-xanthene) as the conjugated system, named BTPA-4, is successfully synthesized and employed as the hole-selective layer (HSL) in colloidal quantum dots solar cells (CQDSCs). The introduction of BTPA-4 layer can significantly prolong effective carrier lifetime (τeff), increase charge recombination resistance (Rrec), and thus diminish the interfacial charge recombination at the PbS-QDs/Au electrode interface. The effect of BTPA-4 as HSL in the device performance is especially significant for the open-circuit voltage (Voc) and power conversion efficiency (PCE), with a ∼ 10% and 15% enhancement respectively, comparing with those of device without the HSL. Furthermore, the PbS CQDSCs with BTPA-4 possessed a noticeably stable property for over 100 days of storage under ambient atmosphere.

Upon mixing acetylacetonedioxime and copper(ii) nitrate in water, the acetylacetonedioxime is spontaneously nitrosated at the central α-carbon and four of the nitrosated ligand molecules and five Cu ions self-assemble into a pentanuclear metallacrown complex, whose structure has been revealed by single crystal X-ray analysis and magnetic interactions between the Cu ions in the complex have been probed. The lability of the core Cu ion in the complex is suggested.

Coordination chemistry of 2,2′-bipyridine bearing an ortho-substituted phenyl group at the 6-position, i.e., 6-(o-X-phenyl)-2,2′-bipyridine (MeO-L: X = OMe; Me2N-L: X = NMe2) with [Ru(ttpy)Cl3] (ttpy = 4′-(4-tolyl)-2,2′;6′,2″-terpyridine) was investigated. The reaction of MeO-L and [Ru(ttpy)Cl3] in the presence of N-methylmorpholine afforded demethylated, O-coordinated complex [Ru(O-L)(ttpy)]+ (O-L: X = O) as well as the cyclometalated, C-coordinated complex [Ru(MeO-L)(ttpy)]+. On the other hand, reaction of Me2N-L and [Ru(ttpy)Cl3] in the presence of N-methylmorpholine afforded only N-coordinated complex [Ru(Me2N-L)(ttpy)]2+. The crystal structures, spectroscopic and redox properties were examined supplemented by DFT calculations. The spectroscopic and redox properties of RuN are more or less similar to those of [Ru(ttpy)Cl3]. On the other hand, the properties of RuC and RuO are mutually similar but significantly different from those of RuN. The anionic ligand in RuC and RuO raises the HOMO energy as compared to the neutral ligand in RuN, which is manifested in negatively shifted redox potentials, particularly the oxidation potentials, and thus, the red shift in the visible absorption band. Relevance of these complexes to sensitizers for dye-sensitized solar cells is briefly discussed.

Self-assembled structures formed from a pyridine-appended zinc chlorophyll derivative are reported. While the zinc complex forms cyclic oligomers in chloroform solution, as indicated by (1)H NMR studies (including diffusion-ordered spectroscopy), vapor pressure osmometry, and cold-spray ionization mass spectrometry, it forms double-stranded helical coordination polymers in the solid state, as revealed by single-crystal X-ray analysis.

We present large area graphene oxide (GO) thin films as a potential transparent electrode fabricated by using simple route. Atomic force microscopy (AFM) topographies showed a uniform film texture that is wrinkle-free with roughness as low as ∼1.4 nm. Desired optical and electrical properties were achieved by thermal reduction at a temperature as low as 170 °C without any reagent; which is an important factor in practical application field. Microstructural perfection is quite evident from the abrupt descent around specific energy of photons in the transmittance spectrum. In particular, we explore that device-quality GO thin films can be obtained via a low-cost scalable technique in comparison with other previous works. Urbach energy and different electrical parameters are addressed. The nature and extent of the band gap are analyzed. The findings are very significant in view of an optimized use of GO thin films in electrical and photoelectric applications.

We have prepared a novel piperidine-donor-substituted perylene sensitizer, PK0002, and studied the photovoltaic performance in dye-sensitized solar cells (DSSCs). Physical properties and photovoltaic performance of this new perylene derivative PK0002 are reported and compared with those of unsubstituted perylene sensitizer, PK0003. PK0002, when anchored to nanocrystalline TiO2 films, achieves very efficient sensitization across the whole visible range extending up to 800 nm. The incident photon-to-current conversion efficiency (IPCE) spectrum was consistent with the absorption spectrum and resulted in a high short-circuit photocurrent density (Jsc) of 8.8 mA cm-2. PK0002 showed higher IPCE values than PK0003 in the 520–800 nm region. Under standard AM 1.5 irradiation (100 mW cm-2) and using an electrolyte consisting of 0.6 M dimethylpropyl-imidazolium iodide, 0.05 M I2, 0.1 M LiI, and 0.5 M tert-butylpyridine in acetonitrile, a solar cell containing sensitizer PK0002 yielded a short-circuit photocurrent density of 7.7 mA cm-2, an open-circuit photovoltage of 0.57 V, and a fill factor of 0.70, corresponding to an overall conversion efficiency of 3.1%.

Properly designed double- and triple-decker porphyrin and/or phthalocyanine complexes assemble themselves into ordered higher-order structures on substrate surfaces. One of the macrocyclic ligands adsorbs on the surface almost always in a face-on fashion on highly oriented pyrolytic graphite and Au(111) surfaces as revealed by means of scanning tunnelling microscopy. For example, well-ordered oriented monolayer assemblies of single-molecule magnets were fabricated. In some cases, the vertical orientation, that is, which ligand adsorbs on the surface, can be controlled by applied potentials. The rotational libration of the top ligand with respect to the adsorbed bottom ligand and hence to the surface has been visualised for a double-decker porphyrin with a molecular beacon. The electronic, magnetic and dynamic properties of double- and triple-decker complexes bode well for the development of molecular devices.

The self-assembled structures of an oxazole-appended zinc chlorophyll derivative in solution and in a crystal are reported. Cyclic oligomers formed in chloroform, while staircase-like coordination ...

We describe the control of the higher-order structures of supramolecular coordination polymers of zinc chlorophyll derivatives by rational design of molecular structure; positional isomers differing in the location of the coordination site lead to staircase-like or helical structures as revealed by X-ray crystallography.

Porphyrins are promising components to be used in molecular electronics due to their rich electronic/photonic properties. Preparation of supramolecular architectures of porphyrins on solid surfaces would constitute a basis for further development toward molecular circuitry or other constructs for molecular electronics applications. Assemblies on surfaces can be probed with scanning tunneling microscopy (STM) at submolecular resolutions to reveal the arrangements and conformations of molecules on an individual molecule basis. The electronic characteristics within a single porphyrin molecule can also be probed by means of the same technique. This review summarizes the status quo of STM studies on porphyrins on surfaces with regard to their assemblies, structures, and electronic properties at the single molecule level.

Photosynthetic antenna arrays found in nature funnel photoexcited energy into the reaction center. Attempts have been made to mimic the antenna function by using artificial chromophores, porphyrins in particular, not only to better understand the energy-transfer processes but also to create light-harvesting devices. This review covers non-covalent porphyrin assemblies, for which intra-ensemble energy-transfer processes were characterized. The essence of the mechanisms of energy transfer is summarized and specific examples are reviewed with an emphasis put on the rate and mechanism of singlet-singlet energy transfer. As these examples demonstrate, non-covalent intra-ensemble energy-transfer processes have been ascribed to the Förster-type through-space mechanism in almost all cases. The exception is porphyrin dyad and pentad from our group based on amidinium-carboxylate salt bridges. Through-bond superexchange mechanism is proposed to account for the fast excited energy-transfer processes for these unique assemblies. The importance of intermolecular interactions not only in terms of the structural aspects but also in terms of the electronic aspects is highlighted for the design of supramolecular systems in which efficient energy transfer is desired.

A star-shaped Ru/Os tetranuclear complex, in which a central Os unit is linked to three peripheral Ru units by 4,4''-azobis(2,2'-bipyridine) (azobpy) bridging ligands, was prepared to examine the unique photodynamics regulated by its redox state. The Ru/Os tetranuclear complex exhibits Ru-based luminescence at 77 K, whereas the three-electron reduction (one for each azobpy) of the Ru/Os complex results in luminescence from the Os unit. The photoexcited state of the Ru/Os complex rapidly decays into low energy metal-to-ligand charge-transfer states, in which the excited electron is localized in the azobpy ligand in the form of azobpy(.-). Upon the one-electron reduction of the azobpy ligands, the above-mentioned low-energy states become unavailable to the photoexcited complex. As a result, an energy transfer from the Ru-based excited state to the Os-based excited state becomes possible. Ultrafast transient absorption measurements revealed that the energy transfer process consists of two steps; intramolecular electron transfer from the terminal bipyridine ligand (bpy(.-)) to form azobpy(2-) followed by a metal-to-metal electron transfer. Thus, the Ru/Os tetranuclear complex collects light energy into the central Os unit depending on the redox state of the bridging ligands, qualifying as a switchable antenna.

Molecular switches based on metal complexes, in which electron and/or energy transfer processes are switched on and off or significantly modulated by externally applied stimuli, such as electrons (redox reactions), light, and chemical substances (protons, ions, and molecules), are reviewed. Also described are single-molecule transistors, in which conductance through a single metal complex is modulated by applied gate voltages.

The azobis(bipyridine) ligand 6,6″-azobis(2,2′-bipyridine) (6-azobpy) was prepared as a new member of the family of azopolypyridine derivatives. This compound undergoes reversible trans/cis photois...

Iridium(III) fac-tris(2-phenylpyridine) fac-[Ir(ppy) 3 ) complexes equipped with long alkyl chains were prepared to examine their capability to form organized arrays on the surface of highly oriented pyrolytic graphite (HOPG). The molecules form lamellar arrays at the 1-phenyloctane/HOPG interface. From the analysis of the STM images, it was concluded that the molecules align with alkyl chains being interdigitated. Similar lamellar arrays were also obtained at the air/HOPG interface upon drop-casting of toluene solutions. The lamellar structure at the molecular level leads to rectangular two-dimensional crystalline domains a few hundred nanometers long (nanoslips). Infrared external reflection spectroscopy suggested that the adsorbed alkyl chains adopt the trans-zigzag conformation in the nanoslip, although the orientations of the zigzag plane of the alkyl groups are mixed. Cyclic voltammetry indicates fast electron transfer between the adsorbed molecules and the substrate and significant intermolecular electronic interactions. It was found that annealing at high temperatures is an effective method to prepare ordered assemblies more than a few micrometer scale (microslips). The orientations of the nanoslips prepared from the racemic mixture exhibited an apparent 12-fold symmetry, while its optically active enantiomer resulted in more irregular domains with a six-fold symmetry, implying an important role of chirality on packing at the molecular level and on the orientation of the domains at larger scales. When drop-cast from more concentrated solutions than a few hundreds of micromolar, multilayers were obtained, in which the alkyl chains in the molecules are more or less perpendicular to the surface. This structure can be transformed into the nanoslips upon standing.

Neat reaction between HgI2 and 1-methyl-2-(phenylazo)imidazole (Pai-Me) under microwave irradiation has isolated a novel compound whose structure shows intercalated HgI2 in the layers of Pai-Me. They exist independently in interpenetrated arrays. In a solution phase study, the same reaction has synthesized an iodo-bridged azoimidazole-Hg(II) complex, [Hg(RaaiR')(mu-I)(I)]2 (RaaiR' = 1-alkyl-2-(arylazo)imidazole). The structures have been characterized by X-ray diffraction studies. Chloro-bridged Hg(II) complexes of azoimidazoles, [Hg(RaaiR')(mu-Cl)(Cl)]2, are also known. These complexes upon irradiation with UV light show trans-to-cis isomerization. The reverse transformation, cis-to-trans isomerization, is very slow with visible light irradiation. Quantum yields (phi t--c) of trans-to-cis isomerization are calculated, and the free ligand shows higher phi than their Hg(II) complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by controlled temperature reaction. The Ea's of free ligands are much higher than that of halo-bridged Hg(II)-azoimidazole complexes. Chloro-bridged Hg(II) complexes show lower Ea's than those of iodo-bridged complexes. DFT calculation has been adopted to rationalize the experimental results.

A coupled light-harvesting antenna-charge-separation system, consisting of self-assembled zinc chlorophyll derivatives that incorporate an electron-accepting unit, is reported. The cyclic tetramers that incorporated an electron acceptor were constructed by the co-assembly of a pyridine-appended zinc chlorophyll derivative, ZnPy, and a zinc chlorophyll derivative further decorated with a fullerene unit, ZnPyC60 . Comprehensive steady-state and time-resolved spectroscopic studies were conducted for the individual tetramers of ZnPy and ZnPyC60 as well as their co-tetramers. Intra-assembly singlet energy transfer was confirmed by singlet-singlet annihilation in the ZnPy tetramer. Electron transfer from the singlet chlorin unit to the fullerene unit was clearly demonstrated by the transient absorption of the fullerene radical anion in the ZnPyC60 tetramer. Finally, with the co-tetramer, a coupled light-harvesting and charge-separation system with practically 100 % quantum efficiency was demonstrated.

Cu substitution raises the degree of (001) crystal orientation perpendicular to the film surface for FeCuPt prepared by Rapid Thermal Annealing (RTA). To increase areal packing density of FeCuPt grains, a SiO2 Substrate having self-organized nano-pores was used as a nano-template. The highly ordered structure of the mesophase thin film is formed by the ordering of self-assembled triblock copolymer micelles, and after annealing at about 600 °C, 8 nm nano-pore arrays formed where there had been micells. Ar-etched SiO2 substrate with self organized nano-pores is effective in increasing the areal packing density and decreasing the size of FeCuPt grains prepared by RTA. An average grain diameter, standard deviation of diameter and areal packing density of FeCuPt grains were 5.9 nm, 1.3 nm and 0.57 (about 3 times the non Cu substituted case), respectively. We observed (001) peak and almost no peak at (111) by x-ray diffraction, where the degree of (001) crystal orientation I(001) / I(111) > 3 means a high rate of ordering orientation, which gives us reliable evidence of ordered FeCuPt grains.

We investigated the dependence of the surface-enhanced Raman scattering (SERS) activity of densely arranged two-dimensional assemblies of spherical Au(core)-Ag(shell) nanoparticles (Au/AgNSs) on the nanoparticle diameter. The size-controlled Au/AgNSs were synthesized using the Au nanosphere seed-mediated growth method without any bulky stabilizers. The diameters of the Au/AgNSs were 38, 53, and 90 nm and the ratio of the total diameter to the Au core diameter was adjusted to ca. 2.0. Extinction spectra of the colloidal solutions of these nanoparticles exhibited the prominent peak of the localized surface plasmon resonance (LSPR) of Ag and therefore the Au/AgNSs exhibited LSPR properties almost the same as Ag nanospheres. It was confirmed from SEM observation that the organic solvent-mediated liquid-liquid interface assembly technique easily generated densely arranged two-dimensional assemblies of the nanospheres. The extinction spectra of all the assemblies exhibited a prominent broad peak ranging from 500 nm to the near-infrared region, which is assigned to the longitudinal LSPR mode of the coupling nanospheres. The extinction intensity increased with increasing nanosphere diameter. The SERS activities of these assemblies were investigated using p-aminothiophenol as a probe molecule. The result revealed that the enhancement factor (EF) of the Raman signal dramatically increased upon increasing the particle diameter. The maximum EF obtained with a laser excitation wavelength of 785 nm was 1.90 × 10(6) for a nanosphere diameter of 90 nm. This renders the two-dimensional assemblies of the plasmonic Au/AgNSs promising for the development of highly sensitive SERS sensor platforms due to their strong electromagnetic effect.

Monolayer arrays of a series of meso-tetra-substituted porphyrins containing octadecyloxy and carboxyl (or pyridyl) groups were prepared on the highly oriented pyrolytic graphite surface at the liquid/solid interface. It was found by means of scanning tunneling microscopy that some porphyrins from this family assemble into various patterns. Specifically, slightly undulated rows are obtained from 5,10,15-tris(4-octadecyloxyphenyl)-20-(4-pyridyl)porphyrin. Meanwhile, rows with more pronounced kinks result from 5-(4-carboxyphenyl)-10,15,20-tris(4-octadecyloxyphenyl)porphyrin. The occurrence of the kinks is dependent on the arrangement of surrounding porphyrin molecules and is determined by intricate interplay between directional hydrogen-bonding interactions and packing forces, including molecule-molecule and molecule-substrate interactions. A double-layer structure is obtained from 5,10-bis(4-carboxyphenyl)-15,20-bis(4-octadecyloxyphenyl)porphyrin, probably through cyclic hydrogen bond formation. This work proves the concept that programmed surface patterning is possible by using porphyrins incorporating directional intermolecular interaction sites.

The effects of substituents at the bay positions for push–pull-type perylenedicarboxylic anhydride dyes on the performance of dye-sensitized solar cells were investigated. The substituents fine-tun...

Several 2- and 3-(phenylazo)pyridine derivatives were prepared. Most of their trans isomers have a large absorption band (∼2 x 10 4 M - 1 cm - 1 (1 M = 1 mol dm - 3 )) around 320 nm and a small absorption band (∼400 M - 1 cm - 1 ) around 450 nm. All of these compounds photoisomerize upon irradiation of the shorter (trans-to-cis) and longer (cis-to-trans) wavelength absorption bands. trans Isomers of 3-(phenylazo)pyridines axially coordinate more strongly to Zn-porphyrins than cis isomers, while the opposite is the case for 2-(phenylazo)pyridines, due to steric reasons. These phenylazopyridines quench the fluorescence of Zn-porphyrin upon coordination. These properties were exploited for the light-triggered fluorescence modulation of Zn-porphyrins. Light was irradiated to a mixed solution of phenylazopyridine and Zn-porphyrin to induce photoisomerization of the phenylazopyridine, which underwent association with, or dissociation from, the Zn-porphyrin, resulting in a decrease or increase of Zn-porphyrin fluorescence. For example, the fluorescence intensity of Zn-tetraphenylporphyrin reversibly changed by up to 50%, when 4-methoxy-2-(phenylazo)pyridine was employed.

A tetranuclear Ru complex linked by 4,4″-azobis(2,2′-bipyridine) (azobpy), [Ru{(azobpy)Ru(bpy)2}3][PF6]8 (bpy = 2,2′-bipyridine) has been prepared and fully characterized. Cyclic and differential pulse voltammetries show that two kinds of oxidation occur, the one at the less positive potential being assigned to the oxidation of the three peripheral Ru ions, while the other to that of the central Ru ion. On a cathodic scan, a pair of three-electron (one electron on each azobpy) reductions of azobpy ligands appear at less negative potentials than terminal bpy ligands. A low-energy metal-to-ligand charge transfer (MLCT) absorption band involving the π*-orbitals of azobpy ligands is observed in addition to the usual MLCT band involving terminal bpy ligands. These results indicate the presence of a low-lying π* level of azobpy. A selective reduction of azobpy ligands renders the non-luminescent complex into a moderately luminescent species. This light switch is reversible, implying the utility of this branched...

Two new ditopic ligands, 5,5"-azobis(2,2'-bipyridine) (5,5"-azo) and 5,5"-azoxybis(2,2'-bipyridine) (5,5"-azoxy), were prepared by the reduction of nitro precursors. Mononuclear and dinuclear Ru(II) complexes having one of these bridging ligands and 2,2'-bipyridine terminal ligands were also prepared, and their properties were compared with previously reported Ru(II) complexes having 4,4"-azobis(2,2'-bipyridine) (4,4"-azo). The X-ray crystal structure showed that 5,5"-azo adopts the trans conformation and a planar rodlike shape. The X-ray crystal structure of [(bpy)(2)Ru(5,5"-azo)Ru(bpy)(2)](PF(6))(4) (Ru(5,5"-azo)Ru) showed that the bridging ligand is in the trans conformation and nearly planar also in the complex and the metal-to-metal distance is 10.0 A. The azo or azoxy ligand in these complexes exhibits reduction processes at less negative potentials than the terminal bpy's due to the low-lying pi level. The electronic absorption spectra for the complexes having 5,5"-azo or 5,5"-azoxy exhibit an extended low-energy metal-to-ligand charge-transfer absorption. The ligands, 5,5"-azo and 5,5"-azoxy, and the mononuclear complex, [(bpy)(2)Ru(5,5"-azo)](2+), isomerize reversibly upon light irradiation. The low-energy MLCT state sensitizes the isomerization of the azo moiety in this complex. While [(bpy)(2)Ru(4,4"-azo)Ru(bpy)(2)](PF(6))(4) exhibits light switch properties, namely, significant electrochromism and a large luminescence enhancement, upon reduction, Ru(5,5"-azo)Ru does not show these properties. The radical anion formation upon reduction of these complexes has been confirmed by ESR spectroscopy.

A new dyad and two triad chromophore compounds containing coumarin, Ru(II) and Os(II) terpyridine-type complexes were synthesized. The dyad is composed of coumarin and Os(II) units, while the triads are composed of coumarin, Ru(II) and Os(II) units. One of the triads has a phenylene spacer to connect the Ru(II) unit and the Os(II) unit, while the other has an azo moiety. Energy transfer in these multichromophoric systems has been probed by electronic absorption and luminescence spectroscopy. The switching behavior of photo-induced energy transfer by redox stimuli in the latter triad has been examined. Photophysical and electrochemical analysis indicates that the contribution of the energy transfer from the coumarin chromophores and the Ru(II) center to the Os(II)-centered emission in the ‘switch-on state’ is estimated to be about 70%. This contribution is larger than that in the previously reported Ru(II)/Os(II) dyad system, which was evaluated to be 40%. Thus, it is concluded that an improved switching of directional energy transfer has been achieved from the coumarin moiety to the Os(II) center in this new triad chromophore system.

A Ru(II) complex containing the 4,4′-diphenyl-2,2′-bipyridine (Ph2bpy) and 7-amino-dipyrido[3,2-a:2′,3′-c]phenazine (dppz-NH2) ligands was synthesized and found to be an excellent switchable photosensitizing unit suitable for photo-induced energy transfer, which has large light absorptivity, superior excited state properties and an amino functional unit for connecting acceptor units. [Os(tpy)2]2+ (tpy = 2,2′:6′,2″-terpyridine) unit was connected to the amino group of this photosensitizing unit by an amide bond to construct a heterodinuclear Ru(II)/Os(II) photo-induced energy transfer system. This system showed stronger Os(II) centered emission compared to the similar heterodinuclear Ru(II)/Os(II) complex containing 2,2′-bipy (bpy) instead of Ph2bpy. Analysis of the photophysical processes of these complexes indicated that the stronger Os(II) emission was ascribed not only to the higher absorptivity but also to the increased energy transfer efficiency from the Ru(II) to the Os(II) center. It also demonstrated that photosensitization by energy transfer to the Os(II) center was switched on and off reversibly by protonation/deprotonation of the dppz moiety.

A new ditopic spacer, N-propylisonicotinamidine, has been developed to assemble a ternary supramolecular complex, zinc-tetraphenylporphyrin (ZnTPP)-spacer-acceptor (3,4-dinitrobenzoic acid), via an axial coordination of the spacer to ZnTPP and a salt bridge interaction between the spacer and acceptor. Formation of this ternary complex was probed by 1 H HMR and UV-vis spectroscopy. The ternary complex is formed with an overall association constant of 1.9 x 10 8 M - 2 in dichloromethane. The fluorescence is nearly completely quenched by the electron acceptor in the ternary complex as confirmed by the steady-state fluorescence measurements. The triplet excited state of ZnTPP is also quenched by the electron acceptor in the ternary complex. The ternary complex is also formed in acetonitrile, where fluorescence quenching is observed with an intracomplex quenching rate constant of 1.9 x 10 9 s - 1 . Photoinduced intracomplex electron transfer is invoked as a likely mechanism of the fluorescence quenching and triplet bleaching.

Three low-cost triphenylamine-based hole-transport materials (HTMs) with spiro[fluorene-9,9-xanthene] (SFX) skeleton are synthesized through a facile three-step procedure. The effect of the chemical structure of the HTMs on the optical property, energy levels, H2O/HTM interface, as well as the perovskite solar cell performance are studied. With the increasing bulkiness of attached groups on the SFX skeleton, the charge recombination resistance at the TiO2/perovskite/HTMs interfaces is gradually increased, leading to increased open-circuit voltages. The device based on the bulkiest HTM (named BTPA-6) exhibits a better solar cell performance (11.57%, area: 1.02 cm2) than those with BTPA-4 and BTPA-5 in the forward scan. BTPA-6 also exhibits a power conversion efficiency of 14.4% (area: 0.375 cm2) which nearly matches spiro-OMeTAD (15.0%) in the reverse scan. Furthermore, all the three cost-effective (∼1/3 of that of spiro-OMeTAD) HTMs exhibit better long-term stabilities than spiro-OMeTAD.

We provide evidence that a heteroleptic double-decker complex of Ce with phthalocyanine and porphyrin ligands undergoes rotational libration in solution for the first time on the basis of variable-...

The development of robust dyes is a highly important theme for any applications of dyes. Here we present photophysical and electrochemical characterization of a set of robust dyes based on the thienylnaphthalimide unit. The set is comprised of the thienylnaphthalimide derivatives with phenyl- (Ph-), 4-nitrophenyl- (NO2Ph-), and 4-(diphenylamino)phenyl (Ph2NPh-) substituents as exemplars covering electron-withdrawing to electron-donating groups. The fluorescence quantum yields of the Ph-TNI increases as the solvent polarity increases, while that of Ph2NPh-TNI showed the opposite trend. Changes in the rates of nonradiative decay were found to be a major factor for these contrasting behaviors. Cyclic voltammetry showed that the substituent effects were more apparent for the HOMO energies rather than the LUMO energies. Density functional theory calculations showed that the first singlet excited state of these compounds is a (1)π,π* state with a significant charge transfer character. Ph-TNI and Ph2NPh-TNI are much more stable against photodegradation than coumarin and fluorescein dyes.

A sharp response of infrared light detecting capability is observed in reduced graphene oxide based photodetector. The photoresponse increased with increasing solution concentration and annealing duration, at a low percolation. The photocurrent increases considerably before saturation and persists for a maximum time of 26 min. This Letter also reports on superiority of device performance with continuous annealing over annealing with an interval. A maximum photoresponsivity of 0.55 A/W and external quantum efficiency of 57% was achieved at low power light intensity (0.8 mW/cm(2)). This Letter presents an efficient graphene oxide thin film infrared photodetector processed via a modified synthesis protocol. (C) 2014 Elsevier B. V. All rights reserved.

Electronic absorption and emission spectra of 4-(dimethylamino)pyridine (DMAP), 3-methyl-4-(dimethylamino)pyridine (MDMAP), and 3,5-dimethyl-4-(dimethylamino)pyridine (TMAP=tetramethylaminopyridine) were measured in cyclohexane (nonpolar), chloroform (medium polar), and acetonitrile (highly polar) solutions. Intense charge transfer emission of DMAP was observed only in acetonitrile, while that of MDMAP and TMAP was observed in all the three solvents. Dynamics of excited electronic states of these molecules is discussed on the basis of steric hindrance between methyl groups at 3- and 5-positions of pyridine ring and dimethylamino groups.

Phthalimide-fused mono(crown ether)s (1 and 2) and bis(crown ether)s (3 and 4) were prepared. These imide derivatives strongly fluoresce in methanol, and the fluorescence intensity is affected by alkali metal ions due to crown-ion interactions. While fluorescence increases upon complexation involving a single macrocycle, it decreases when the fluorophores take a face-to-face arrangement. This property was used to monitor the process of ion complexation and concomitant conformation changes. With the incremental addition of cesium ions (M) to the bis(crown ether)s (L), a folded sandwich complex (LM) initially formed, which subsequently transformed into a more extended LM2-type complex. This behavior, which was independently confirmed by 1H NMR spectroscopy, is clearly manifested in the fluorescence intensity.

Shuttlecock- and bowl-equipped 4-(phenylazo)pyridine derivatives, which bear substituents that allow the pyridine moiety to protrude in the trans form but hinder it in the cis form, have been designed and synthesized. These molecules show cis/trans photoisomerization despite the presence of bulky substituents. 1 H NMR titration with Zn-porphyrin showed that the trans isomers coordinate to Zn-porphyrin much stronger than the cis isomers.

A series of mononuclear Ru trisbypiridine complexes connected to an anthraquinone unit by a flexible alkyl chain of varying lengths and a bolaamphiphilic dinuclear ruthenium complex bearing an anthraquinone unit in the middle of alkyl chain spacers were synthesized. Their conformational preference in CH3CN and in dihexadecyl phosphate vesicles was probed by utilizing the intramolecular electron-transfer quenching of the metal-to-ligand charge-transfer excited state of the Ru center by the appended quinone moiety. The length of the alkyl chain spacer had little effect on the quenching efficiency in either medium. A marked difference in the quenching behavior was observed only in the case of the dinuclear Ru complex in vesicles. These results indicate that the bolaamphiphilic structure is necessary and effective for the set of immobilized molecules to take a stretched conformation spanning a bilayer membrane.

A bis-crown ether derivative of triaminotriazine was synthesized via a phthalic acid derivative of a polyether macrocycle obtained from benzo-18-crown-6. It exists in different conformers distinguishable by 1H NMR at room temperature, in which the macrocyclic side-arms take a closed, half-open, or fully open form, due to the rotational barrier of the C(triazine)–N bond. Large alkali metal ions, such as Rb+ and Cs+, the latter being particularly effective, promote the formation of the closed conformer. A barbiturate derivative also causes a similar equilibrium shift to the closed form by establishing complementary hydrogen bonds. The half-open and fully open conformers are induced by smaller alkali metal ions than Rb+, among which K+ is the most effective.

The Ni(II) complex of 6,6′-bis(hexylbenzoylamino)-2,2′-bipyridine (LH2) in square-planar symmetry underwent a reversible and simultaneous deprotonation of the two amide units. The non-deprotonated complex (NiLH22+) showed high SCN− selectivity by the preferential axial coordination of two SCN− molecules (log KSCN = 8.11 ± 0.03 in CH2Cl2 at 20 °C), while the deprotonated complex showed little affinity toward anions. Deprotonation-induced affinity-switching of the complex by the external aqueous layer mediated an efficient SCN−-selective up-hill transport across a CH2Cl2 liquid membrane by coupling with the symport of protons from pH 4.0 to 6.0 aqueous solutions. Equilibrium at the aqueous/organic interface could be represented by the equation Kapp = ([Ni(LH2)(SCN)2]org)/([NiL]org[H+]2aq[SCN−]2aq), where Kapp is the equilibrium constant (log Kapp = 13.6 at 20 °C). However, the rates of protonation and deprotonation of the complex at the interface were dependent mostly on the concentration of the complex in ...

Properties of ‘sandwich’ charge-transfer (CT) complexes composed of bis-anthracene host compounds, in which two anthracences are connected by an anthraquinone spacer, and various aromatic acceptors have been systematically studied. Complexation stronger than that seen in monomer model compounds was observed in all cases. Thermodynamic analysis revealed that this enhanced binding to acceptors is due to larger enthalpic gain accompanied by a lower entropy loss effected by preorganization of the host. The major factor that determines the association constants is not the strength but the steric features of acceptor. Binding constants for fluorenones with nitro residues in the bay region are smaller because of the bulkiness of the substituents. It has been established that the CT complexes are of the weak bπ–aπ type from the analysis of the CT absorption energy. Complexation-induced chemical shifts in the 1H NMR spectra indicate highly oriented guest inclusion and have revealed some geometrical features of the complexes.

Pyrrole-imidazole polyamides are versatile DNA minor groove binders and attractive therapeutic options against oncological targets, especially upon functionalization with an alkylating agent such as seco-CBI. These molecules also provide an alternative for oncogenes deemed "undruggable" at the protein level, where the absence of solvent-accessible pockets or structural crevices prevent the formation of protein-inhibitor ligands; nevertheless, the genome-wide effect of pyrrole-imidazole polyamide binding remain largely unclear to-date. Here we propose a next-generation sequencing-based workflow combined with whole genome expression arrays to address such issue using a candidate anti-cancer alkylating agent, KR12, against codon 12 mutant KRAS. Biotinylating KR12 enables the means to identify its genome-wide effects in living cells and possible biological implications via a coupled workflow of enrichment-based sequencing and expression microarrays. The subsequent computational pathway and expression analyses allow the identification of its genomic binding sites, as well as a route to explore a polyamide's possible genome-wide effects. Among the 3, 343 KR12 binding sites identified in the human LS180 colorectal cancer genome, the reduction of KR12-bound gene expressions was also observed. Additionally, the coupled microarray-sequencing analysis also revealed some insights about the effect of local chromatin structure on pyrrole-imidazole polyamide, which had not been fully understood to-date. A comparative analysis with KR12 in a different human colorectal cancer genome SW480 also showed agreeable agreements of KR12 binding affecting gene expressions. Combination of these analyses thus suggested the possibility of applying this approach to other pyrrole-imidazole polyamides to reveal further biological details about the effect of polyamide binding in a genome.

The metal-enhanced fluorescence (MEF) based on the localized surface plasmon resonance (LSPR) of metal nanoparticles (nanostructures) is one of useful optical phenomenon to achieve the low detection limits of fluorescence-based biosensors. The enhancement mechanism has been suggested to be due to a photoexcitation enhancement and a plamson-exciton coupling effect. However, commonly-used metal nanoparticles in this research field have been composed of only expensive metal, e.g. Au and Ag, because these generate strong local electromagnetic fields within the visible wavelengths, which can significantly enhance the molecular fluorescence. The high material cost is not suitable for the practical application. The Cu metal is suitable for the industrial use because of the low material cost. Furthermore, the LSPR of the Cu nanoparticles is induced within the visible region. Therefore, the use of the Cu nanostructures as a light-harvesting center is worthy of attention. However, the two critical problems should be resolved for the utilization of the Cu LSPR. First, the LSPR of the traditional spherical Cu nanoparticles generate at around 570 nm where the interband transition of Cu from 3d to the Fermi level is occurred. The strong interband transition damps the LSPR excitation. Therefore, the generating wavelength of the Cu LSPR was tuned to the longer wavelength, i.e. above 590 nm, where the interband transition efficiency is very low. Second, the Cu is susceptible to the spontaneous oxidation in air. The resultant Cu2O layers also damp the Cu LSPR. Therefore, the development of the efficient oxidation suppression technique of the Cu surfaces is important. Recently, we succeeded in significantly enhancing the fluorescence of porphyrin immobilized on the periodic Cu structures, which were fabricated using a two-dimensional colloidal crystals of silica particles as a template (denoted as Cu half-shell arrays: CuHSs(d); dis the underlying silica diameter). However, the fluorescence enhancement ability of the plasmonic Cu nanostructures, as compared with the Au nanostructures known as a traditional fluorescence enhancement platform is still not clear. Our goal in this study is to evaluate the enhancement ability of the Cu nanostructures from the comparison with that of Au nanostructures. The silica colloidal crystals on glass plates (25 × 18 mm)were prepared by a previously-reported bottom-up procedure using silica particles with diameter of 226, 346, and 552 nm.1 The Cu with 100 nm in thickness was deposited onto the crystal surfaces by thermal deposition via a modification of mercaptopropyltriethoxysilane. As a reference sample, a planar Cu plate (CuP) was prepared by depositing Cu on a bare glass plate. The Au half-shell arrays (AuHSs(d)) were prepared by depositing Au with the same thickness as Cu in the same manner. Tetracarboxyphenyporphyrin (TCPP) as a fluorescence probe molecule was immobilized on the arrays by a surface sol-gel method viaa modification of the self-assembled monolayer of mercaptohexadecanoic acid (MHA) as a surface oxidation-suppressing ultrathin films (denoted as TCPP/CuHS(AuHS)). In order to calculate the local electromagnetic fields of the arrays, finite difference time domain (FDTD) method were used. The strong local electromagnetic fields were expected to be generated at the spatial gap region between the neighboring silica particles in the CuHS as well as the AuHS. The LSPR generating wavelength was red-shifted to longer wavelengths with increasing the underlying silica diameter for both of the CuHS and the AuHS. (586, 630, and 552 nm for the CuHS(226), CuHS(346), and CuHS(552), respectively and 594, 670, and 890 nm for AuHS(226), AuHS(346), and AuHS(552), respectively). We confirmed from the fluorescence excitation spectra of the TCPP/CuHSs (and AuHSs) at the fluorescence wavelength of 715 nm that the molecular fluorescence was significantly enhanced in all of the samples. Also, the fluorescence signals from the TCPP/CuHS were 10-fold weaker than those from the TCPP/AuHS. On the other hand, quenching efficiency of the fluorescence on the CuP was significantly higher than Au. Therefore, the Cu nanostructures have the combination of fluorescence enhancement and quenching abilities. As a result, we demonstrated that the Cu LSPR was useful for the fluorescence-based switching sensing and device applications. 1. K.Sugawa et al. ACS Nano 2013, 7, 9997 Figure 1

Nano-sized metal particles have been received great attention in the field of bioimaging and therapy, i.e. cancer treatment, because of their unique optical properties resulting from localized surface plasmon resonance (LSPR). Multifunctional nanoparticles have been developed for the precisive diagnosis and noninvasive cancer therapy in place of traditional surgery and chemotherapy, which can be restricted by region, physical strength, and so on. While various metal nanoparticles have been explored, the use of those consisting of Ag has been limited because of their physical instability. In particular, Ag nanoprisms (AgPRs) can be easily degraded by thermal energy generated along with the LSPR excitation because of their high surface energy. However, use of the AgPRs will provide a sufficient possibility for precisive cancer diagnosis due to the generation of significantly-enhanced electromagnetic fields. In this study, we developed AgPRs-based Pt-Ag alloyed nanomaterials (AgPtPRs), which can act as multifunctional therapeutic/diagnostic agents with improved thermal stability and bioimaging capability. The Ag nanoprisms (AgPRs) exhibiting a peak within near-infrared (NIR) wavelengths were synthesized according to the method reported by Mirkin.1) The formation of the AgPRs with an average edge length of 40 nm and thickness of 8nm were confirmed by TEM images. The AgPtPRs were synthesized by galvanic replacement of the as-prepared AgPRs with hexachloroplatinic (IV) acid. After the reaction, while the size as well as the morphology of them were almost maintained, the plasmon extinction peak slightly red-shifted. This result implies that thin Pt layers formed over the AgPRs surfaces. Thermal-durability evaluated by the irradiation of a continuous laser (2 W, 808 nm) for 1 h and heating in waterbath at 95 °C for 1 h. The morphology of the non-alloyed AgPRs were easily degraded by both of the laser irradiation and the exterior heating because of their high vertices energy. The optical properties of the AgPRs were destroyed by the deformation. In contrast, thermal-durability of the AgPtPRs against both of them was appreciably improved by the alloying reaction with Pt atoms. The photothermal conversion efficiency (PCE) obtained by the irradiation of NIR laser (808 nm, 2 W) were calculated to be ca. 65% even after the alloying reaction. The value was quite higher than those of the previous-reported major photothermal nanoparticles, e.g. Au nanorods (22 %) and Au nanoshells (13 %).2) In order to search the source of the higher PCE, the scattering and absorption components consisting of the extinction were calculated using a simulation of boundary element method (BEM). The absorption of the AgPRs modeled as the triangular structures with edge length of 40 nm and the thickness of 8 nm was dominant in the extinction peak. The optical tendency was almost maintained even after covering the AgPRs with Pt thin shells with 0.4 nm in thickness. The factor of large PCE of AgPtPRs and AgPRs was considered to be due to the high absorption coefficient. Next, we evaluated the effect of the photothermal phenomenon of AgPtPRs on the cancer cells. After the Hela cells were incubated with various concentrations of AgPtPRs modified with folic acid-conjugated polyethyleneimine, the cells were washed with phosphate buffered saline (PBS) several times. While the irradiation of the laser with 808 nm (2W) to the cells incubated with the AgPtPRs led to the efficient death of cells, non-incubated cells was not affected by the irradiation. The cell viability with and without the laser irradiation was ca. 12.9 % and 87.3 %, respectively. It was found from these results that the AgPtPRs have sufficient ability as a photothermal therapy nanomaterial with a high biocompatibility. In order to evaluate the imaging ability, surface-enhanced Raman scattering (SERS) properties of 4-mercaptobenzonic acid (4-MBA) immobilized on the nanoprisms were measured with a NIR laser of 785 nm. Those on the AgPRs and AgPtPRs showed Raman peaks characteristic of 4-MBA at 1590 cm-1 (C-C stretching) and 1080 cm-1(ring breathing). These results demonstrated that the strong local fields generated even after covering with the Pt shell led to the enhancement of the Raman signals for the SERS-imaging technique. 1). G. S. Métraux et al., Adv. Mater., 2005, 17, 412. 2). C. M. Hessel et al., Nano Lett., 2011, 11, 2560. Figure 1

Introduction Plasmonic metal-nanostructured electrodes have been used for the development of high-performance organic photoelectric conversion systems because they can act as superior light-harvesting nanoantennae. Many previous reports have demonstrated that this optical phenomenon led to a substantial enhancement of the photocurrent from porphyrin dyes. The enhancement mechanism has been suggested to be a significant enhancement of the photoexcitation efficiency of the dyes, which were located within the strong local electromagnetic fields generated via a localized surface plasmon resonance (LSPR) of the metal nanostructures. However, all of the plasmonic electrodes reported so far are composed of expensive metallic species (Au and Ag). We believe that the components of the plasmonic electrodes should be inexpensive and that the enhancement of photoelectric conversion efficiency using “inexpensive plasmonic nano-antenna materials” is an important goal because one of the main advantages of the organic photoelectric conversion systems is low cost due to the use of organic dyes. In this study, we fabricated photoelectric conversion systems consisting of hybrids of porphyrin molecules as a dye and a plasmonic Cu arrayed electrode because the Cu material is significantly cheaper than the traditional plasmonic materials. Experimental section The arrayed electrodes were fabricated by thermally-depositing Cu onto the two-dimensional silica colloidal crystals consisting of silica particles with 160, 260, and 330 nm in diameters.1 Effective suppression of the spontaneous oxidation of the Cu electrodes by protecting with the ultrathin layers consisting of mercaptohexadecanoic acid and the ultrathin sol-gel layers of Ti(O) and polyvinyl alcohol has allowed us to accurately evaluate the Cu nanoantenna effect on the porphyrin photocurrent. The porphyrin monolayers were immobilized onto the surface of the colloidal crystals. Results and Discussions The Cu LSPR could be tuned from visible to near-infrared wavelengths by controlling the underlying silica diameter. The resultant LSPR above 600 nm was efficiently excited where the interband transition is comparatively low. Also, the molecular ultrathin films, which covered the Cu surfaces, effectively suppress the spontaneous oxidation in the air and electrolyte aqueous solution. Photocurrent measurements for porphyrin-immobilized Cu arrayed electrodes (working electrode) were carried out in an aqueous 0.1 M NaClO4 solution containing 5 mM methyl viologen dichloride as an electron acceptor, using a three electrode photoelectrochemical cell. Ag|AgCl (sat. KCl aq.) and platinum wire were used as the reference and counter electrodes, respectively. Photocurrents generated by irradiation of the monochromated light from a Xe lamp were detected. As a result, we have succeeded in efficiently enhancing the photocurrent from the porphyrin up to approximately 54 times by tuning the generating wavelength of Cu nanoanntena to the wavelengths above 600 nm, as compared with those generated from the porphyrin-immobilized Cu planar electrode. In a previous study, we reported that the nanoantenna effect from the Au arrayed electrodes enhanced the porphyrin photocurrent up to approximately 15 times.2 Therefore, this study demonstrates that the plasmonic Cu electrodes, which have combined strong light harvesting antenna effect and low material cost, are very useful for improving the performance of organic photoelectric conversion systems. Therefore, this is an important basic research which can accelerate the practical application of highly-efficient plasmonic photoelectric conversion systems. References 1. Sugawa, K.; Tamura, T.; Tahara, H.; Yamaguchi, D.; Akiyama T.; Otsuki J.; Kusaka Y.; Fukuda, N.; Ushijima H., ACS Nano 2013, 7, 9997-10010. 2. Sugawa, K.; Hirono, S.; Akiyama, T.; Yamada, S., Photochem. Photobiol. Sci. 2012, 11, 318.

We synthesized anisotropic Pd nanoplates for use as a novel refractive index (RI) sensing material in the visible region. The nanoplates showed an extinction peak that was attributed to the excitation of the localized surface plasmon resonance at ~620 nm in the visible region. It was found that the peak was red-shifted with increasing the RI of the surrounding medium. The susceptibility was calculated to be 250 nm per RI unit, comparable to some anisotropic Au nanoparticles that are excellent RI sensing materials.

We have prepared a novel sandwich-type double-decker porphyrin complex with cerium, in which one of the porphyrins has long alkyl chains and the other has a pendant free-base porphyrin unit. The preparation of the complex was achieved with a Sonogashira coupling reaction between a preformed double-decker complex bearing an ethynyl moiety and an iodophenyl porphyrin. This complex forms moderately ordered self-assembled monolayers at the interface of 1-phenyloctane and highly oriented pyrolytic graphite. STM images with submolecular resolution revealed that the double-decker complexes form monolayers through adsorption of the alkyl-substituted porphyrin unit, presenting the other porphyrin having the additional porphyrin unit to the solution. All molecules are oriented in the same direction within single ordered domains. The double-decker complex and the corresponding free-base porphyrin form mixed monolayers due to their common adsorbing group and the matching unit cell parameters. The high spots for the double-decker cores are accompanied by lower spots, which can be assigned as the pendant free-base porphyrin units, revealing that the double-decker complexes predominantly take perpendicular orientation, in which the additional porphyrin unit orients perpendicular to the molecular row. Both the double-decker complex and the free-base porphyrin adsorb on the surface initially after the mixture was deposited, but the double-decker complex is gradually replaced by free-base porphyrin toward the thermodynamically stable assembly, in which the free-base porphyrin predominates. This behavior is unique to this particular complex among some analogous complexes with the same adsorbing group, which implies that groups not directly involved in adsorption may have profound effects on the adsorption and assembling properties of the molecule.