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Water-soluble λ-carrageenan–benzophenone complexes retained their properties of crystallization-induced phosphorescence of benzophenones at room temperature in aqueous solutions.

Red phosphorescence emissions in the longer-wavelength region can be produced by introducing methoxy groups and bromine atoms into the electron-accepting benzothiadiazole dye.

The regulation of multicolor fluorescence changes in mechanochromic fluorescence (MCF) remains a challenging task. Herein, we report the regulation of MCF using a donor-acceptor structure. Two crystal polymorphs, BTD-pCHO(O) and BTD-pCHO(R) produced by the introduction of formyl groups to an MCF dye, respond to a mechanical stimulus, allowing a three-color fluorescence change. Specifically, the orange-colored fluorescence of the metastable BTD-pCHO(O) polymorph changed to a deep-red color in the amorphous-like state to finally give a red color in the stable BTD-pCHO(R) polymorph. This change occurred by mechanical grinding followed by vapor fuming. The two different crystal packing patterns were selectively regulated by the electronic effect of the introduced functional groups. The two types of selectively formed crystals in BTD(F)-pCHO bearing fluorine atoms, and BTD(OMe)-pCHO bearing methoxy groups, respond to mechanical grinding, allowing for the regulation of multicolor MCL from a three-color change to two different types of two-color changes.

Organic porous fluorescent materials created by supramolecular noncovalent synthesis can be developed for fluorescent sensing applications. In this study, we report a noncovalent synthesis of a near-infrared porous fluorescent crystal and its solvent vapor-responsive fluorescence change. The donor–acceptor type phenothiazine–thiadiazolopyridine dye emits near-infrared fluorescence at 727 nm in the as-prepared state. The near-infrared emission band is shifted to 792 nm upon application of mechanical grinding and subsequent chloroform vapor-fuming. The resulting fumed sample has a porous crystal structure with a pore size larger than 5.75 A. The electron-donating phenothiazine and electron-accepting thiadiazolopyridine moieties are closely one-dimensionally stacked through multiple noncovalent interactions, and the created one-dimensional architectures are two-dimensionally organized through an alternative arrangement of the phenyl groups on the phenothiazine rings, resulting in a three-dimensional porous structure. This near-infrared porous fluorescent crystal responds to the polarity difference of solvent vapors (from nonpolar hexane to polar methanol) incorporated inside the pore site, providing fluorescence wavelength and intensity changes.

During the self-assembly of π-conjugated molecules, linkers and substituents can potentially add supportive noncovalent intermolecular interactions to π-stacking interactions. Here, we report the self-assembly behavior of thienopyrrole-fused thiadiazole (TPT) fluorescent dyes that possess ester or ether linkers and dodecyloxy side chains in solution and the condensed phase. A comparison of the self-association behavior of the ester- and ether-bridged compounds in solution using detailed UV-vis, fluorescence, and NMR spectroscopic studies revealed that the subtle replacement of the ether linkers by ester linkers leads to a distinct increase in the association constant (ca. 3-4 fold) and the enthalpic contribution (ca. 3 kcal mol

Fluorescence change systems that can respond to biological objects have attracted attention for use as biological probes and sensors. In this study, we report emission enhancement in a fluorescent aggregate composed of amphiphilic donor-acceptor dye molecules. The emission efficiency of the aggregate was reduced upon introducing a hydrophilic galactopyranose moiety, because of the decrease in the aggregate stability, which in turn was due to disruption of the hydrophilicity-hydrophobicity balance. In contrast, emission enhancement could be achieved by treatment with β-galactosidase, as a result of the removal of the galactopyranose moiety. The change in aggregate stabilization based on the hydrophilicity-hydrophobicity balance leads to the emission enhancement into detectable β-galactosidase activity.

Mechanical stimuli-responsive fluorescence changes, a phenomenon referred to as mechanochromic fluorescence (MCF), have attracted much interest in novel materials and biological applications. Herein, we report MCF based on a donor–acceptor structure bearing nonplanar donor moieties that allows the tuning of emission color and regulation of emission change direction. The MCF is demonstrated using a series of triphenylamine-based donor–acceptor dyes. The fluorescence wavelength can be tuned by the strength of the donor–acceptor conjugation, yielding blue to deep-red fluorescence. The twisted conformation as well as the continuous internal space created by the steric demand of the donor moieties enables rearrangement of the crystal packing upon mechanical grinding, leading to fluorescence changes. The bathochromic and hypsochromic shifts in MCF are regulated by the presence or absence of stacking interactions with the central acceptor moiety.

The two-photon excitation technique has several advantages such as reduced autofluorescence and deeper penetration in tissues, less photodamage and photobleaching, and higher three-dimensional resolution, which cannot be achieved by linear one-photon excitation. Because of these advantages, two-photon absorption (TPA) of organic molecules has been developed in biological and materials science fields. In particular, fluorescent TPA dyes have attracted the attention of chemists as well as biologists because of their application in biological imaging. At present, various types of fluorescent TPA dyes that have large TPA cross sections as well as good fluorescence quantum yields are accessible. However, the fluorescent color has mostly been restricted to the shorter wavelength region of blue and green light, which competes with the autofluorescence from intrinsic biomolecules. To achieve efficient two-photon imaging, the longer wavelength emission of red and near-IR light is required for two-photon excitation because this light lies in the biological optical window. In this chapter, we focus first on fluorescent TPA dyes that have red and near-IR light-emitting properties. Then, we summarize the recent advances made in the development of these dyes for applications in biological systems. In the last section, the unique features of two-photon absorption in aggregate systems are summarized.

A metal-free organic carbazole-pyrimidine dye exhibiting phosphorescence-fluorescence dual emission was developed into a white-light emission-switching system. The two crystal polymorphs obtained by breaking the molecular symmetry responded to the external stimuli of heating, vapor-fuming, and mechanical grinding, resulting in a tricolor switching system that includes white-light emission.

Micelle formation and red-light fluorescence emission of benzothiadiazole (acceptor)−triphenylamine (donor) amphiphilic molecules in water/methanol solutions explored with synchrotron small-angle X-ray scattering.

Turn-on-type emission enhancement and ratiometric emission color change in star-shaped donor–acceptor dyes in an aqueous medium are reported. In a THF/water medium, the hexaazatriphenylene dye, bearing six triphenylamine moieties 2, indicated that the emission was significantly quenched in low water volumes, but was recovered and enhanced in high water volumes. This turn-on-type emission enhancement is attributed to aggregate formation, which restricts emission quenching. In addition to emission enhancement, an emission color change was observed in another donor–acceptor dye 1 bearing an additional benzene spacer between the hexaazatriphenylene and triphenylamine moieties. The initial orange light emission at 0% water fraction changed to a green light emission at 40–90%, with the quenching of a red light emission at 10–30%. This unusual double emission change was attributed to the combination effect of aggregation and twisted intramolecular charge-transfer. In contrast, both turn-on-type and ratiometric emission changes were not found in dyes 3 and 4, which lacked triphenylamine donor moieties.

A pixel in an uncooled microbolometer terahertz (THz) focal plane array (FPA) has a suspended structure above read-out integrated circuit (ROIC) substrate. An optical cavity structure is formed between a thin metallic layer deposited on the suspended structure and a thick metallic layer deposited on the ROIC surface. The geometrical optical cavity length for our previous pixel structure, 3–4 μm, is extended three times, so that responsivity can be increased in the sub-THz region. This modification is carried out by depositing a thick SiN layer on the thick metallic layer. The modified pixel structure is applied to 640 × 480 and 320 × 240 THz-FPAs with 23.5 μm pixel pitch. Minimum detectable powers per pixel (MDP) are evaluated for these FPAs at 4.3, 2.5, 0.6, and 0.5 THz, and the MDP values are found to be improved by a factor of ten at 0.6 and 0.5 THz. The MDP values of the THz-FPAs developed in this work are compared with those of other THz detectors, such as uncooled antenna-coupled CMOS (complimentary metal-oxide semiconductor) THz-FPAs and cooled bolometer arrays. It is found that our THz-FPAs are more sensitive in the sub-THz region than the CMOS THz-FPAs, while they are much less sensitive than the cooled bolometer arrays. These THz-FPAs are incorporated into a 640 × 480 THz camera and 320 × 240 THz camera, and imaging equipment is developed. The equipment consists of a linearly polarized sub-THz source, a collimator lens, a beam homogenizer, two wire grids, a quarter-wave plate, and two THz cameras, and sub-THz images are demonstrated. It should be mentioned for the equipment that imaging of transmission and reflection is realized by moving only the quarter-wave plate, and the reflection image is taken along a direction normal to a sample surface so that the reflection image is hardly deformed.

We report the synthesis and photovoltaic properties of a donor–acceptor polymer, poly(naphthobisthiadiazole-triphenylamine) [poly(NTD-TPA)], which consists of TPA as a donor unit and NTD as a stronger acceptor than benzothiadiazole. This polymer had an absorption edge at wavelengths up to 610 nm. The optimized bulk-heterojunction (BHJ) organic photovoltaic (OPV) cell using poly(NTD-TPA) and [6,6]-phenyl C71 butyric acid methyl ester (PC 70 BM) exhibited a short-circuit current of 6.87 mA cm −2 , an open-circuit voltage V oc of 0.79 V, a fill factor of 0.40, and a power conversion efficiency of 2.15%. The validities of these photovoltaic properties are discussed using the incident-photon-to-current conversion efficiency, film morphology, field-effect hole mobility, and electroluminescence (EL) spectrum from the charge transfer states between the highest occupied molecular orbital of poly(NTD-TPA) and the lowest unoccupied molecular orbital of PC 70 BM. In particular, the V oc estimated from the current density–voltage curve agreed well with that estimated from the peak energy of the EL spectra.

In this paper, we report a systematic study on the light-emitting behavior of a series of triphenylamine-based donor–acceptor-type dyes in the solution and solid states as well as in the aggregated state in polar aqueous media. The emission band shifted bathochromically along with the decrease in the fluorescence quantum yield as the solvent polarity was increased from nonpolar cyclohexane to polar DMF. In a THF/water medium, the emission was quenched in a low water volume, whereas the emission was recovered and increased in a high water volume. In a low water volume, the dye molecules exist in a monomeric form, and the fluorescence quenching increases with increasing water fraction, similar to that observed in the solvent-polarity-dependence study. In contrast, the dye molecules aggregated in a high water volume. This is probably because the inside of aggregates is less polar than the outside, thus preventing nonradiative deactivation and recovering the emission. This unusual emission was achieved by triphenylamine-based dyes containing a relatively strong acceptor moiety such as quinoxaline, benzothiadiazole, and thiadiazolopyridine, providing longer-wavelength red and near-IR emission. In the benzothiadiazole-based dyes, when the phenyl groups in the donor moieties were replaced with methyl groups, the fluorescence quantum yield decreased, indicating that the triphenylamine donor moiety is suitable for emission in the aggregated state. The nonplanar structure of triphenylamine disrupts an ordered packing and produces a less-ordered spherical aggregate, leading to an efficient light emission even in polar aqueous media.

Triphenylamine-naphthobisthiadiazole-based donor-acceptor-donor dyes were prepared and their aggregation and light-emitting behaviors were investigated. Deep-red light was emitted between 650–680 nm in a solution of tetrahydrofuran and dichloromethane with moderate fluorescent quantum yield of 0.36–0.48. However, when the solvent system was changed to THF/water, emission behavior became dependent on the solvent ratio. For lower water concentrations, emission intensity decreased significantly when the ratio of water to THF was increased. The donor-acceptor-donor molecules exist as monomers, and an increase in solvent polarity favors the fluorescence quenching that results from solvation. However, emission intensity recovered and intensified progressively at higher water concentrations. The molecules form aggregates, which provide a less polar hydrophobic space within to restrict solvation and quenching, ultimately allowing emission.

The applicability of a blackbody source to sensitivity measurements and calibration of an uncooled Terahertz (THz) focal plane array (FPA) is discussed, but the combination of a blackbody source and a band-pass filter may not be suitable for these purposes. Two ways to measure the minimum detectable power (MDP) of uncooled THz-FPAs are described and compared when used with strong THz sources such as a quantum cascade laser (QCL). The MDP is defined as the radiant power that produces a signal-to-noise ratio of unity in the output of a THz imager that uses a THz-FPA operating at a TV frame rate. One method (method 1) is based on the hypothesis that the beam pattern of the THz source is close to a Gaussian pattern. In another method (method 2), the signal level of the background in an image that does not contain a THz source is subtracted from the signal of the image. While method 2 is more flexible, how large the signals coming from THz source should be, as compared with the noise level, remains to be defined. Finally, based on issues with the current non-uniformity correction (NUC) technique, specifications are proposed for THz source power and wobbling technique to obtain uniform illumination for an ideal NUC technique.

In this paper, we report the preparation and red-light-emitting behavior of benzothiadiazole–tris(alkyloxy)phenylethene dyes. In solution, we observed an efficient red light emission with high fluorescence quantum yields (up to 0.78). With increase in solvent polarity, the emission bands shifted to longer wavelengths accompanied by a large Stokes shift of up to 152 nm. A moderate fluorescence quantum yield of 0.52 could be achieved even in the polar solvent dimethylformamide. Red light emission with good fluorescence quantum yields (up to 0.50) was also observed in the bulk solid, liquid, and film state.

Cholesterol-appended benzothiadiazole–triphenylamine two-photon absorption dye was prepared and its self-assembling nature was investigated. The dye gave viscous fluid organogels in aliphatic hydrocarbon solutions such as cyclohexane, in which one-dimensional supramolecular aggregates are formed through the van der Waals interactions among the cholesterol moieties and the intermolecular hydrogen-bonding interactions among the carbamate spacer moieties. The supramolecular self-assembling was confirmed by the line-broadening effect in the 1 H NMR spectra, and by the bathochromic shifts of the absorption and emission bands. The bathochromic shift of the absorption band suggested that the benzothiadiazole–triphenylamine moieties take a J -like aggregation mode. Under the self-assembled conditions, the dye showed a negative exciton splitting pattern in the CD spectrum, suggesting the one-dimensional stacking with a left-handed twisting mode. The two-photon absorption nature in the parent benzothiadiazole–triphenylamine chromophore is maintained in the self-assembled system.

This paper reports the self-assembling and two-photon absorption natures of donor–acceptor molecules, tri(phenanthro)hexaazatriphenylene (TPHAT-C) and tri(phenanthrolino)hexaazatriphenylene (TPHAT-N), bearing six electron-donating moieties. In the 1H NMR spectra, a line-broadening effect, arising from self-assembled aggregation was observed. Several hundred nanometer scale aggregates were detected in dynamic light scattering. The one-dimensional aggregation of the TPHAT molecules was indicated by the concentration dependence in UV/vis one-photon absorption and one-photon excited fluorescence spectroscopies. An enhancement of the two-photon absorption cross-section was observed in the self-assembled TPHAT system. The order of the two-photon absorption nature is in agreement with the order of the aggregative nature.

The authors developed terahertz (THz) imager which incorporates 320x240 focal plane array (FPA) with enhanced sensitivity in sub-THz region (ca. 0.5 THz). The imager includes functions such as external-trigger imaging, lock-in imaging, beam profiling and so on. The function of the external-trigger imaging is mainly described in this paper, which was verified in combination of the THz imager with the pulsed THz free electron laser (THz-FEL) developed by Osaka University. The THz-FEL emits THz radiation in a wavelength range of 25 - 150 μm at repetition rates of 2.5, 3.3, 5.0 and 10 pulses per second. The external trigger pulse for the THz imager was generated with a pulse generator, using brightening pulse for THz-FEL. A series of pulses emitted by the THz-FEL at 86 μm were introduced to the THz imager and Joule meter via beam splitter, so that the output signal of THz imager was normalized with the output of the Joule meter and the stability of the THz radiation from FEL was also monitored. The normalized output signals of THz imager (digits/μJ) obtained at the repetition rates mentioned above were found consistent with one another. The timing-relation of the external trigger pulse to the brightening pulse was varied and the influence of the timing-relation on beam pattern is presented. These experimental results verify that the external trigger imaging function operates correctly.

An amorphous polymer, poly(BTD-TPA), which consists of benzothiadiazole and triarylamine units, can be successfully utilized to fabricate bulk heterojunction (BHJ) organic photovoltaics (OPVs), and the OPV performance can be demonstrated to be independent of the casting solvent or thermal annealing temperature. The OPV based on poly(BTD-TPA):PC 70 BM (1:4) that was fabricated using chloroform (boiling point of 61 °C) and annealed at 60 °C for 10 min exhibited a power conversion efficiency (PCE) of 2.81% under simulated solar irradiation through an air mass of 1.5 at 100 mW cm −2 . On the other hand, the OPV fabricated using o -dichlorobenzene (boiling point of 181 °C) and annealed at 110 °C for 10 min exhibited a PCE of 2.65%. Almost the same PCEs and incident photon to current conversion efficiencies (IPCEs) were obtained in both OPVs. The use of an amorphous film of poly(BTD-TPA) in the fabrication of OPVs offers great advantages over the use of a polycrystalline film of regioregular poly(3-hexylthiophene) (P3HT) in terms of high reproducibility of the OPV performance.

A comparative study of the properties of bulk-heterojunction organic photovoltaic cells (OPVs) using a benzothiadiazole (BTD)–triphenylamine (TPA) small molecule and its polymerized molecule (poly(BTD-TPA)) is presented. OPVs using BTD-TPA or poly(BTD-TPA):PC60BM at a 1 : 2 mixing weight ratio were fabricated. The power conversion efficiency (PCE) of the poly(BTD-TPA)-based OPV was twice that of the BTD–TPA-based OPV. The field-effect hole mobility of poly(BTD-TPA) is two orders of magnitude higher than that of BTD–TPA and the absorption peak of poly(BTD-TPA) is at a longer wavelength than that of BTD–TPA. Accordingly, the improved hole mobility and enhanced absorption of AM1.5 solar-simulated light led to a high short-circuit current (Jsc) and PCE in OPVs based on poly(BTD-TPA). Using OPVs with poly(BTD-TPA):PC70BM (1 : 4), the device performance exhibited a Jsc value of 7.45 mA cm−2, an open-circuit voltage of 0.92 V, a PCE of 2.65%, and incident photon to current conversion efficiencies of around 50% at wavelengths ranging from 360 to 560 nm. The experimental results for the OPVs with BTD–TPA-based materials indicate that the polymer is effective for obtaining high-performance OPVs.

This paper reports the self-assembling and electrochemical nature of hexaazatriphenylene-based electron-deficient heteroaromatics with an expanded π-electron system. The tri(phenanthro)hexaazatriphenylenes (TPHAT-Cs) and tri(phenanthrolino)hexaazatriphenylenes (TPHAT-Ns) were prepared by condensation reactions of the corresponding phenanthrenequinones and phenanthrolinediones, respectively, with hexaaminobenzene. Their electron affinity was indicated from cyclic voltammetry measurements, in which the first reduction potentials were evaluated at around -1.7 V (vs Fc/Fc(+)) in dichloromethane. In nonpolar and polar solvents and in the film state, the TPHAT-Cs and TPHAT-Ns formed one-dimensional aggregates with an H-type parallel stacking mode. In the MALDI-TOF mass spectra, significant peaks were seen at several multiples of the parent ion up to tetramer aggregates. The (1)H NMR spectra indicated a line-broadening effect due to the aggregation. The UV-vis and fluorescence spectra showed a concentration dependence, which is attributed to a dynamic exchange between the monomer and aggregate species. The order of the aggregative nature was estimated from the concentration dependence and the fluorescence quantum yield. By replacement of the peripheral aromatic moieties instead of the phenanthrene (TPHAT-Cs) with the phenanthroline (TPHAT-Ns), the aggregative nature was enhanced.

X-ray scattering from an organogel made from discotic triazine triamide was measured at SPring-8 at a quite wide q range of 0.050 nm−1

We studied three different benzothiadiazole-triphenylamine (BTD-TPA) derivatives as donor materials for bulk-heterojunction organic photovoltaics (OPVs), and investigated the resulting OPV performance. We found that the increased concentration of (6,6)-phenyl C61 butyric acid methyl ester (PCBM) as acceptor material and the decreased thickness of active layers led to high-performance OPVs with sufficient percolated pathways for the photogenerated mobile carriers to the respective electrodes. The highest performance was observed for OPVs based on BTD-Th-TPA:PCBM (1:2, w/w) with thickness of 76 nm, yielding a power-conversion efficiency of 1.0% under 100 mW/cm2 of AM 1.5 illumination and incident photon conversion efficiency of 32% at a wavelength of 540 nm.

LSI on-chip optical interconnections are discussed from the viewpoint of a comparison between optical and electrical interconnections. Based on a practical prediction of our optical device development, optical interconnects will have an advantage over electrical interconnects within a chip that has an interconnect length less than about 10mm at the hp32-22nm technology node. Fundamental optical devices and components used in interconnections have also been introduced that are small enough to be placed on top of a Si LSI and that can be fabricated using methods compatible with CMOS processes. A SiON waveguide showed a low propagation loss around 0.3dB/cm at a wavelength of 850nm, and excellent branching characteristics were achieved for MMI (multimode interference) branch structures. A Si nano-photodiode showed highly enhanced speed and efficiency with a surface plasmon antenna. By combining our Si nano-photonic devices with the advanced TIA-less optical clock distribution circuits, clock distribution above 10GHz can be achieved with a small footprint on an LSI chip.

An active terahertz (THz) imaging system that can easily be switched between a transmission and a reflection mode is developed. The system consists of a compact THz source that operates at room temperature, optical system utilizing polarization and two 640×480 pixel uncooled THz cameras. In order to take an image of a large sample, a part of the imaging system is moved at a fixed distance and a series of images taken are combined to one elongated image. Concealed nonmetallic object detection in an envelope is demonstrated.

Both 640×480 and 320×240 terahertz (THz) imagers were developed whose sensitivity were improved in sub-THz region by a factor of 10. The imagers include functions such as external-trigger imaging, lock-in imaging, beam profiling and so forth. The function of the external-trigger imaging was verified, using the pulsed THz free electron laser developed by Osaka University.

Uncooled microbolometer-type 640x480 and 320x240 Terahertz (THz) focal plane arrays (FPAs) with enhanced sensitivity in sub-THz region are developed, and incorporated into 640x480 and 320x240 cameras, respectively. The pixel in the THz-FPA has such a structure that an area sensitive to electromagnetic wave is suspended above read-out integrated circuit (ROIC). A thin metallic layer is formed on the top of the sensitive area, while a thick metallic layer is formed on the surface of ROIC. The structure composed of the thin metallic layer and the thick metallic layer behaves as an optical cavity. The THz-FPAs reported in this paper have a modified pixel structure which has several times longer optical-cavity length than NEC’s previous pixel does, by forming a thick SiN layer on the ROIC. The extended optical-cavity structure is favorable for detecting electromagnetic wave with lower frequency. Consequently, the Minimum Detectable Power per pixel (MDP) is improved ten times in sub-THz region, especially 0.5-0.6 THz. This paper presents spectral frequency dependences of MDP values for THz-FPA with the modified pixel structure and THz-FPA with the previous pixel structure, using THz free electron laser (FEL) developed by Osaka University. The modification of pixel structure extends high sensitivity region to lower frequency region, such as sub-THz region, and the wider spectral coverage of THz camera surely expands its applicability

In this paper we report the self-assembling nature of fluorescent hexaazatriphenylenes (HATs) 6a-d with six alkyl/alkoxy-chain-containing biphenyl groups and their application to light-harvesting antennae. In a nonpolar solvent and the film state, the HAT derivatives form one-dimensional aggregates with an H-type parallel stacking mode, which were analyzed by 1H NMR, UV-vis, and steady-state and time-resolved fluorescence spectroscopy. When HAT derivative 7 with six perylenediimide moieties is incorporated into the one-dimensional aggregates, an efficient energy transfer takes place from the self-assembled HAT moiety as a light-harvesting antenna to the perylenediimide moiety as an energy acceptor. Further, when HAT derivative 8 with six triphenylamino moieties is newly added to the light-harvesting system, an intermolecular electron transfer occurs subsequently between the electron-accepting perylenediimide molecule and the electron-donating triphenylamino molecule.

[reaction: see text] Large disk-shaped aromatic tri(phenanthrolino)hexaazatriphenylenes 5a, 5b, and 5c with six butyl, dodecyl, and 4-octylphenyl groups, respectively, were self-assembled both in solution and film state to form one-dimensional aggregates. Their n-type semiconducting nature was indicated from CV measurement, in which the first reduction potentials were evaluated at around -1.7 V (vs Fc/Fc(+)) in dichloromethane.

A number of fluorescent benzothiadiazole dyes have been synthesised and their optical properties, when dispersed in a liquid crystal host phase, examined. These dyes have five linearly π-conjugated aromatic ring systems (both with and without ethene and 1,3-butadiene spacers). The liquid crystalline host medium, used was the nematic phase of MLC-2039. The emission colours observed ranged from green to red, depending on the unsaturated chains attached at the 4- and 7- positions of the bezo-2,1,3-thiadiazole core. A highly dichroic and efficient fluoresence was observed. The dye 4,7–bis[5-bis(phenylethenyl)thiophen-2-yl]-2,1,3-benzothiadiazole is of particular importance. This is the first example of a dye emitting strong red fluorescence (633 nm). When dispersed in MLC-2039, dichroic ratio values up to 12.3 were obtained.

In this study, we report a preparation and an aggregate emission behavior of an amphiphilic donor–acceptor dye, which is composed of a triphenylamine–benzothiadiazole donor–acceptor chromophore and two water-soluble hexa(ethylene glycol) chains. The dye is strongly fluorescent in nonpolar solutions such as cyclohexane and toluene, whereas the emission intensity is reduced in aprotic polar solutions such as DMF and acetonitrile. This fluorescence reduction correlates with the increase in polarity, by which the transition from a local excited state to a highly polarized excited state is facilitated, leading to an increased nonradiative deactivation rate. Furthermore, significant fluorescence quenching is observed in protic polar solutions such as ethanol and methanol. Hydrogen-bonding interactions between the dye and the protic solvent molecules further accelerate the deactivation rate. In contrast, in a water solution, red light emission is achieved distinctly at 622 nm with a relatively large fluorescence quantum yield of 0.20. This red emission is related to the aggregation of the dye molecules grown in water. The kinetic analysis from the fluorescence rate constant and nonradiative rate constant indicates that the nonradiative deactivation channel is restricted in water. The formed aggregate, which was indicated by transmittance electron microscopy as a spherical aggregate morphology with a diameter of 3–4 nm, provides a less polar hydrophobic space inside the aggregate structure, by which hydrogen-bonding and the subsequent quenching are restricted, leading to the reduction of the nonradiative deactivation rate.

1,4,5,8,9,12-Hexaazatriphenylenes, 1,4,5,8-tetraazaphenanthrene, and quinoxalines, each with six, four, and two N,N-diphenylaminobiphenyl and N,N-diphenylaminophenyl groups, respectively, were prepared and their absorption and fluorescent spectral behaviors were investigated. These compounds showed strong fluorescent solvatochromism arising from the donor-acceptor nature of the π-electron-deficient aromatic core and π-electron-rich diphenylamino terminal groups.

[reaction: see text]. Six perylene diimide-appended hexaazatriphenylene, HAT-PDI(6), was self-assembled in both solution and film state to form a highly stabilized dimer aggregate, in which an efficient energy transfer occurs from the hexaazatriphenylene core to the perylene-diimide moiety.

This paper reports unique and unusual formations of columnar liquid crystals and organogels by self-assembling discotic molecules, which are composed of an aromatic hexaazatriphenylene (HAT) core and six flexible aromatic side chains. In HAT derivatives 3a, with 4'-(N,N-diphenylamino)biphenyl-4-yl chains, 3b, with 4'-[N-(2-naphthyl)-N-phenylamino]biphenyl-4-yl chains, and 3c, with 4'-phenoxybiphenyl-4-yl chains, the two-dimensional hexagonal packings can be created by their self-assembling in the liquid crystalline phase, which were characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. In certain solvents, HAT molecules 3a-c can form the viscoelastic fluid organogels, in which one-dimensional aggregates composed of the HAT molecules are self-assembled and entangled into three-dimensional network structures. The organogel structures were analyzed by scanning electron microscopy observation, (1)H NMR, UV-vis, and circular dichroism spectroscopy. In contrast to 3a-c, none of the liquid crystalline and organogel phases could be formed from 3d and 3e with short aromatic side chains including a phenylene spacer, and 3f (except a few specific solutions) and 3g without terminal diarylamino and phenoxy groups. In 3a-c, the aromatic side chains with terminal flexible groups make up soft regions that cooperatively stabilize the liquid crystalline and organogel supramolecular structures together with the hard regions of the hexaazatriphenylene core.

The molecular dyad C60-(BTD-TPA) consisting of an electron donor triphenylamine-appended 2,1,3-benzothiadiazole chromophore (BTD-TPA) unit covalently linked to an electron acceptor [60]fullerene has been synthesized. The photoinduced electron transfer in C60-(BTD-TPA) has been studied in polar and nonpolar solvents using time-resolved transient absorption and fluorescence measurements. By fluorescence lifetime measurements in picosecond time regions, the excitation of the C60 moiety leads to the formation of C60•--(BTD-TPA)•+ efficiently via the singlet excited state of the C60 moiety. Excitation of the BTD-TPA moiety leads to initial energy transfer to 1C60*- (BTD-TPA), from which electron transfer occurs to form C60•--(BTD-TPA)•+. In the nanosecond time region, C60•--(BTD-TPA)•+ in which the radical cation (hole) delocalizes in the BTD-TPA moiety is persistent for 690 ns in DMF at room temperature. From the temperature dependence of the charge-recombination rate constants, which gave the Marcus paramete...