Highly Emissive Whole Rainbow Fluorophores Consisting of 1,4-Bis(2-phenylethynyl)benzene Core Skeleton: Design, Synthesis, and Light-Emitting Characteristics.

To create the whole-rainbow-fluorophores (WRF) having the small Δλem (the difference of λem between a given fluorophore and nearest neighboring fluorophore having the same core skeleton) values (<20 nm) in full visible region (λem: 400-650 nm), the high log ε (>4.5), and the high Φf (>0.6), we investigated molecular design, synthesis, and light-emitting characteristics of the π-conjugated molecules (D/A-BPBs) consisting of 1,4-bis(phenylethynyl)benzene (BPB) modified by donor groups (OMe, SMe, NMe2, and NPh2) and an acceptor group (CN).

Meso-disubstituted anthracenes with fluorine-containing groups: synthesis, light-emitting characteristics, and photostability.

Synthesis, photophysical properties, and photostability of 9,10-disubstituted anthracenes with fluorine-containing groups (FCG) are described. The values of phi(f) and lambda(em) greatly go up by the meso-substitution with FCG, and a nice corelationship between phi(f) and A(pi) (magnitude of pi conjugation length in the excited single state) is observed. The C6F5 group at the meso positions exhibits an excellent ability in the photostability as well as in the emission efficiency.

How the pi conjugation length affects the fluorescence emission efficiency.

How the pi conjugation length affects the fluorescence emission efficiency is elucidated by examination of the theoretical and experimental relationship between absolute quantum yield (Phi(f)) and magnitude (Api) of the pi conjugation length in the excited singlet state, which provides a novel concept for molecular design for highly fluorescent organic compounds. As a tool to predict Phi(f) from a structural model, (nu(a) - nu(f))1/2 x a3/2 (nu(a): wavenumber of absorption maximum, nu(f): wavenumber of emission maximum, a: molecular radius) could be used instead of Api. The concept should be valuable for potential applications to (1) examination of an excited singlet state structure (for example, coplanarity of excited-state molecules) and (2) molecular design of novel materials, in which the excited singlet state plays an important role, such as highly efficient fluorophores, electroluminescent materials, photoconducting materials, and nonlinear optical materials.

Photophysical properties of oligophenylene ethynylenes modified by donor and/or acceptor groups.

To create highly fluorescent organic compounds in longer wavelength regions, and to gain physical chemistry insight into the photophysical characteristics, we investigated photophysical properties (Phi(f), lambda(em), tau, lambda(abs), epsilon, k(r), and k(d)) and their controlling factor dependence of the following pi-conjugated molecular rods consisting of p-phenyleneethynylene units modified by donor (OMe) and/or acceptor (CN): (1) side-donor modification systems (SD systems), (2) side-acceptor modification systems (SA systems), and (3) systems consisting of donor block and acceptor block (BL systems). As a result, very high Phi(f) values (>0.95) were obtained for BL systems.

Block modification of rod-shaped pi conjugated carbon frameworks with donor and acceptor groups toward highly fluorescent molecules: synthesis and emission characteristics.

To create organic molecules that are highly fluorescent at a longer wavelength region, we investigated the synthesis (using Pd-catalyzed cross-coupling) and photophysical properties (Phi(f), lambda(em), tau, lambda(abs), and epsilon) of the following pi conjugated molecular rods consisting of p-phenyleneethynylene units modified by donor (OMe) and/or acceptor (CN) groups: (1) side-donor modification systems (SD systems), (2) side-acceptor modification systems (SA systems), and (3) systems consisting of a donor block and an acceptor block (BL systems). As a consequence, very high Phi(f) values (>0.95) were obtained for BL systems.

Rigid molecular architectures that comprise a 1,3,5-trisubstituted benzene core and three oligoaryleneethynylene arms: light-emitting characteristics and pi conjugation between the arms.

In view of increasing interest in light-emitting materials, we have investigated the light-emitting characteristics and occurrence of conjugation between arms of star-shaped rigid molecules that comprise a 1,3,5-triethynylbenzene core and methoxy group-substituted oligo(p-phenylethynylene) arms. Consequently, we achieved the ultimate goal (Phif approximately 1.0, log epsilon > 5) for organic molecules with respect to light-emitting ability by creating very intense violet-blue (8, Phif = 0.

New fluorophores with rod-shaped polycyano pi-conjugated structures: synthesis and photophysical properties.

[reaction: see text] Novel rod-shaped polycyano-oligo(phenyleneethynylene)s were synthesized by Pd cross-coupling reaction. Polycyano groups were found to greatly improve the emission efficiency (Phi(f)) of OPEs. By the end donor modification, we achieved the creation of very intense blue light-emitting fluorophore with the SMe group (Phi(f) = 0.

Light-emitting efficiency tuning of rod-shaped pi conjugated systems by donor and acceptor groups.

In view of the increasing importance of highly efficient light-emitting materials in chemistry, biological science, and materials science, we investigated the light-emitting efficiency tuning of rod-shaped oligo(p-phenylene ethynylene)s (OPEs, trimeric to pentameric systems) by donor and acceptor groups, so that they emit the very intense fluorescence (Phif approximately 1.0, log epsilon approximately 5) at 460 nm as the desired wavelength region. This goal was achieved by side modification by MeO (donor) groups and end modification by a CN-substituted benzene ring or CF3-substituted pyridine ring (acceptor) of tetrameric p-phenylene ethynylene rod-shaped molecules (Phif = 0.

Reducing ability of supramolecular C60 dianion toward C=O, C=C and N-N bonds.

Different from C60 dianion which readily reacts with electrophiles, supramolecular C60 dianion (2) generated from gamma-cyclodextrin-bicapped C60 (1) and NaBH4 (or diborate) in DMSO-H2O (9:1, v/v) is able to reduce N-N+, C=C-EWG and C=O bonds to provide the respective dihydro derivatives; 1-mediated reduction of acetophenone with NaBH4 in the presence of (Me2N)2CH2 and EtONa gives turn over frequency (TOF)/h of 400.

Buckminsterfullerenes: a non-metal system for nitrogen fixation.

In all nitrogen-fixation processes known so far--including the industrial Haber-Bosch process, biological fixation by nitrogenase enzymes and previously described homogeneous synthetic systems--the direct transformation of the stable, inert dinitrogen molecule (N2) into ammonia (NH3) relies on the powerful redox properties of metals. Here we show that nitrogen fixation can also be achieved by using a non-metallic buckminsterfullerene (C60) molecule, in the form of a water-soluble C60:gamma-cyclodextrin (1:2) complex, and light under nitrogen at atmospheric pressure. This metal-free system efficiently fixes nitrogen under mild conditions by making use of the redox properties of the fullerene derivative.

Shape-persistency and molecular function in heteromacrocycles: creation of heteroarenecyclynes and arene-azaarenecyclynes.

On the basis of our concept that the introduction of heteroatoms and shape-persistency into the pi-macrocycles should bring forth striking functions or properties, heteroarenecyclynes (such as oxaarenecyclynes and thiaarenecyclynes) with semi-shape-persistent structure, and arene-azaarenecyclynes with shape-persistent structure have been prepared. Their novel functions and characteristic properties are disclosed. Noteworthy is that heteroarenecyclynes include C(60) to provide a Saturn-type complex with a N(2) binding function.