Solid-State Photoluminescence of Diphenylnaphthalenes Studied by Photophysical Measurements and Crystallographic Analysis.

Thanks to recent developments in spectrophotometric instruments, the spectra, quantum yields (Φ), and lifetimes () of photoluminescence from organic and inorganic compounds can be readily determined not only in solution but also in the solid state. It is known that naphthalene emits fluorescence in solution, but not in the solid state. In a previous paper, we reported that solid-state emission can be seen from biaryl compounds comprised of chromophores that show no emission in the solid state.

Asymmetric synthesis of spiro[oxindole-3,2'-pyrrolidine]s through organocatalytic 1,3-dipolar cycloaddition cycloreversion of precursor isatinimine homodimers.

The chiral amine catalyzed diastereo- and enantioselective [3 + 2] cycloaddition between isatin-derived azomethine ylides and α,β-unsaturated aldehydes was successfully carried out to afford spiro[oxindole-3,2'-pyrrolidine]s. It was anticipated that the formation of azomethine ylides occurred the cycloreversion of dispirooxindole-imidazolidines, which are precursor imine homodimers, in aqueous solvents.

Photoinduced Crystal-to-Liquid Transition of Acylhydrazone-Based Photoswitching Molecules.

A photoinduced crystal-to-liquid transition (PCLT) behavior of new acylhydrazone derivatives (NCs) is reported. The photoswitching of the NCs was identified as a negative photochromism with a high -to- conversion yield (>98%). A kinetic analysis shows a half-life of almost one month.

Spectroscopic Tracking of Salicylideneaniline Photocolored Crystals: An Attempt to Quantify Polymorph-Dependent Features toward Precise Structure-Function Correlation Analysis.

Three polymorphs of salicylideneaniline (SA) were prepared, and their photochromic behavior was examined using a recently developed single-crystal microscopic UV-vis spectroscopy approach. This system enabled us to acquire absorption data during the bleaching process as a function of temperature and visible light intensity. First, we demonstrated that, in contrast to the generally accepted assumption, the bleaching curves were notably influenced by the degree of photosaturation at the initial stage.

Ratchet-like mechanism in a long-life photoproduct of salicylideneaniline enclathrated in a pillared-layer guanidinium disulfonate structure.

Salicylideneaniline (SA) was found to exhibit extraordinary long-life photochromism upon being included in a cavity of guanidinium organosulfonate and exhibited a lifetime of ∼30 times that of a pure SA crystal. Crystal structure analysis suggested that the sulfonate molecule in the apo-host provided a flexible cavity space that kinetically trapped SA in its photo-isomerized form, as if it was locked by a ratchet-like mechanism.

Cold Crystallization and the Molecular Structure of Imidazolium-Based Ionic Liquid Crystals with a -Nitroazobenzene Moiety.

The cold crystallization mechanism of 1-{[4'-(4″-nitrophenylazo)phenyloxy]}hexyl-3-methyl-1-imidazol-3-ium tetrafluoroborate ionic liquid crystal was investigated based on thermal analysis, structural analysis, infrared spectroscopy, and quantum chemical calculations. By conducting thorough structural characterization, we found that the prerequisite for cold crystallization is the irreversible molecular conformational alteration induced by the initial heating of the as-grown crystal into a smectic liquid crystal. The originally linear cation molecule bends and forms a step-stair conformation that persists throughout the subsequent heating and cooling processes as phase transition occurs from the crystal phase to the liquid crystal phase and then to the isotropic liquid phase.

A superelastochromic crystal.

Chromism-color changes by external stimuli-has been intensively studied to develop smart materials because of easily detectability of the stimuli by eye or common spectroscopy as color changes. Luminescent chromism has particularly attracted research interest because of its high sensitivity. The color changes typically proceed in a one-way, two-state cycle, i.

Development of Imidazo[1,2- a]pyridine Derivatives with an Intramolecular Hydrogen-Bonded Seven-Membered Ring Exhibiting Bright ESIPT Luminescence in the Solid State.

Imidazo[1,2- a]pyridine derivatives with different hydroxyaryl units (1-3), which could potentially form an intramolecular hydrogen-bonded seven-membered ring in either a planar or a twisted conformation, were newly developed, and the effect of conformation and steric repulsion on the excited-state intramolecular proton transfer (ESIPT) luminescence was evaluated. Among them, 1 and 2 formed an intramolecular hydrogen-bonded seven-membered ring in the crystalline state and exhibited efficient ESIPT luminescence in the solid state (quantum yield up to 0.45).

Single-crystal UV-vis spectroscopic examination of a striking odd-even effect on structure and chromic behaviour of salicylidene alkylamines.

We have found that a series of N-(5-bromosalicylidene) alkylamines exhibited distinct chromic behaviour depending on the parity of their alkyl chain length. A group with an even number of carbon atoms in the alkyl chain showed photochromism, while another group with odd number showed thermochromism.

Systematic investigations on fused π-system compounds of seven benzene rings prepared by photocyclization of diphenanthrylethenes.

We studied the photoproducts of 1-(n-phenanthryl)-2-(m-phenanthryl)ethenes (nEm; n, m = 1, 3 and 9) for understanding photocyclization patterns based on NMR spectroscopy. The crystal structures of the photoproducts were analyzed by X-ray crystallography, and the photophysical features of the photocyclized molecules were investigated based on emission and transient absorption measurements. Phenanthrene derivatives substituted at the 1- and 3-positions were prepared for synthesizing nEm by photocyclization of stilbene derivatives.

Synthesis and Properties of Salicylaldehydes Fine-Tuned by Modular Assembly using "Plug-and-Socket"-Type Extendibility.

A salicylaldehyde derivative bearing four pyridine arms, 3,5-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-2,4-dihydroxybenzaldehyde (Hbpsal) as a "socket", was prepared and used to derive a series of zinc complexes with various extra anions "plugged" into their vacant site. The crystal structure and H NMR spectra were noticeably influenced by the extra anions, allowing fine-tuning of the properties by "plug-and-socket"-type modification. Similar to unsubstituted salicylaldehyde, the zinc complexes reacted with primary amines to afford Schiff-base compounds.

Spontaneous ligand nitrosation and self-assembly into a pentacopper metallacrown complex.

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.

Spectroscopic tracking of Schiff base compounds' hydrogen bonding reorganization associated with solid-to-solid phase transition.

A series of 2,6-dihydroxynaphthalene-1-methylidene alkylamines whose alkyl chain lengths ranged from 9 to 12 was spectroscopically examined. Transmission ultraviolet-visible absorption microspectroscopy revealed that the spectra of solid thin-films of the crystalline samples showed two distinct profiles depending on polymorphs as well as on alkyl chain length. We concluded that these spectral changes occurred not because of conventional intramolecular proton transfer but because of the molecules' interactions with an external proton source, that is, the intermolecular proton transfer.

Spontaneous helical folding of bis(Ni-salphen) complexes in solution and in the solid state: spectroscopic tracking of the unfolding process induced by Na(+) ions.

Four kinds of bis(Ni-salphen) complexes containing a 2-methylenepropane-1,3-diyl linker were synthesised and characterised. Crystal structural analysis revealed that one of the complexes folded into a helical structure, in which two Ni atoms were at a distance of 3.2 Å from each other.

Mutual interference between intramolecular proton transfer sites through the adjoining π-conjugated system in Schiff bases of double-headed, fused salicylaldehydes.

We synthesized two constitutionally isomeric bis(iminomethyl)-2,6-dihydroxynaphthalenes, namely, α,α-diimines 1 and β,β-diimines 2, which can be formally represented as fused salicylaldimines with resonance-assisted hydrogen-bonding sites. Spectroscopic data show that the OH/OH, NH/OH, and NH/NH forms of 1 were in equilibrium in solution and that the proportion of the NH-bearing tautomers increased as the solvent polarity increased. The UV spectra of thin solid films of 1 with various types of hydrogen-bonding networks differed from one another, and the spectral profiles were markedly temperature dependent, whereas the spectra of 1 in the molten state showed quite similar profiles.

Amphiphilic sulfamide as a low-molecular-mass hydrogelator: A novel mode of 3-D networks formed by hydrogen-bond-directed 2-D sheet assemblies.

Asymmetrically substituted amphiphilic sulfamide, N-tetradecyl-N'-(6-dimethylaminohexyl)-sulfamide (3c) having a dimethylamino group at one end of the side chain, showed a strong ability to form two-dimensional (2-D) sheet-like assemblies by the 2-D hydrogen-bond networks between sulfamide moieties. Upon protonation of the amino group with acid, the cationic ammonium form of 3c induced effective hydrogelation (minimum gelation concentration: 0.5wt%) to yield a translucent, self-standing hydrogel.

Dry micromanipulation of supramolecular giant vesicles on a silicon substrate: highly stable hydrogen-bond-directed nanosheet membrane.

Guanosine derivative 1 forms hydrogen-bond-directed giant vesicles. On a silicon substrate, the vesicles retain their shape and internal water phase even after removal of external water under vacuum. Dry manipulation of the micrometer-sized vesicles was carried out via AFM-tip-induced partition and fusion of the vesicles.

Hydrogen-bond-directed 2-D sheet assemblies of sulfamide derivatives: formation of giant vesicles with patchwork-like surface pattern.

Sulfamide derivatives showed high ability to form hydrogen-bond-directed two-dimensional (2-D) sheet assemblies of nanometer thickness. Further, fine-tuning of the side chain structures and preparation conditions allowed for the formation of micrometer-sized giant vesicles of 4b in water by the simple injection method. IR and XRD studies indicated that 4b having tetradecyl and oxyethylene-terminated alkyl side chains formed hydrogen-bond-directed 2-D nanosheet pairs.

Hydrogen-bond-directed giant unilamellar vesicles of guanosine derivative: preparation, properties, and fusion.

By mixing a small volume of THF containing guanosine derivative 1 and tetraethylenegrycol dodecyl ether (TEGDE) with water and subsequently removing TEGDE by gel permeation chromatography, micrometer-sized giant unilamellar vesicles (GUV) of 1 were successfully prepared. The vesicle membrane was a 2-D sheet assembly of thickness 2.5 nm, composed of a 2-D inter-guanine hydrogen-bond network.

Blue/red linear dichroic emission from a highly anisotropic crystal of triarylmethane dye conjugated with phenoxo-zinc complexes.

We have developed a novel triphenylmethane-based hexanuclear zinc complex that exhibits peculiar photochemical and photophysical properties. Upon UV irradiation, the compound turned from colorless to reddish purple, while the color of emission turned from blue to red. The color change was attributed to an oxidation of the ligand part.

Induction of micronuclei in germinating onion seed root tip cells irradiated with high energy heavy ions.

Effects of high LET charged particles on a perfect in-vivo system are an essential theme for the study of the biological effects of radiation. Germinating onion seeds are independent complete organisms and the radiation induced micronuclei in the root chip cells can be examined quantitatively and theoretically. We irradiated with three types of high energy accelerated heavy ions germinating onion seeds using a synchrotron and observed micronuclei in the root tip cells.

Hydrogen-bond-directed giant vesicles of guanosine derivatives in water: formation, structure, and stability.

Hydrogen-bond-directed giant supramolecular vesicles (diameter 1.20 +/- 0.30 microm (SD)) of an alkylsilylated deoxyguanosine derivative, 2a, were prepared faciley by mixing a small volume of a 2a/THF solution with water.

Experimental and theoretical studies on constitutional isomers of 2,6-dihydroxynaphthalene carbaldehydes. Effects of resonance-assisted hydrogen bonding on the electronic absorption spectra.

We prepared and characterized a series of mono- and dicarbaldehydes of 2,6-dihydroxynaphthalene that bear potential resonance-assisted hydrogen bonding (RAHB) unit(s). X-ray crystal structures of selected compounds revealed that each salicylaldehyde moiety forms an intramolecular hydrogen bond and that the introduction of formyl groups into either the alpha- or beta-position causes a considerable difference in geometry, which was interpretative from a conventional scheme of resonance hybrids including ionic state. Analyses on NMR chemical shifts suggested that the compounds in solution are present as an equilibrium mixture between closed and open forms with respect to RAHB units.

Switchable antenna: a star-shaped ruthenium/osmium tetranuclear complex with azobis(bipyridine) bridging ligands.

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(.