Yumi Nakaike

Synthesis of 4‑Substituted 3,5-Dinitro-1,4-dihydropyridines by the Self-Condensation of β‑Formyl-β-nitroenamine

3,5-Dinitro-1,4-dihydropyridines (DNDHPs) are readily constructed by the acid-promoted self-condensation of β-formyl-β-nitroenamines. In the DNDHPs, one molecule of the nitroenamine serves as a C3N1 building block and the other serves as a C2 block. This synthetic method does not require any special reagents and conditions. When the reaction is conducted in the presence of electron-rich benzene derivatives, arylation at the 4-position of DNDHP is achieved by trapping the 3,5-dinitropyridinium ion intermediate.

Flapping viscosity probe that shows polarity-independent ratiometric fluorescence

A variety of fluorescent molecular viscosity probes have been widely used for mapping the local viscosity in cells and for monitoring the microenvironments in materials. However, their viscosity-sensing structural design still relies strongly on molecular rotors featuring intramolecular rotational dynamics. Here we report flapping molecules (FLAP) as a ratiometric viscosity-sensing fluorophore that shows polarity-independent dual fluorescence. Viscosity-sensing mechanism is based on a unique V-shaped-to-planar conformational change in the singlet excited state (S1), in which the flexible motion of an eight-membered ring plays an important role. Fast conformational dynamics have been studied by time-resolved spectroscopies, and the viscochromic properties have been quantitatively analyzed. Application of FLAP to monitoring the curing process of epoxy resins has also been demonstrated, in which other typical environment-sensitive dyes did not work as a local viscosity probe.

Construction of 3,5-dinitrated 1,4-dihydropyridines modifiable at 1,4-positions by a reaction of β-formyl-β-nitroenamines with aldehydes

A novel and efficient method for the synthesis of 4-substituted 3,5-dinitro-1,4-dihydropyridines by a reaction of β-formyl-β-nitroenamines with aldehydes was developed. The reaction of nitroenamines with aldehydes leading to 1,4-dihydropyridines and the self-condensation of nitroenamines leading to pyridinium salt intermediate proceed competitively. The obtained 3,4,5-trisubstituted-1,4-dihydropyridines readily transformed into the corresponding pyridines in high yields.

Impact of photon recycling on carrier recombination processes in CH 3 NH 3 PbBr 3 single crystals revealed by time-resolved two-photon-excitation microscopy

Recently, lead-halide perovskites CH<inf>3</inf>NH<inf>3</inf>PbX<inf>3</inf> (X = I, Br, and Cl) are attracting considerable attention as a new class of photonic device materials. Especially in case of thin-film solar cells based on perovskite CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf>, the high power conversion efficiency (exceed 22%) has been already achieved and to attain the long-term stability and large-area device fabrication become major research topics to realize practical application for perovskite solar cells. The outstanding properties of CH<inf>3</inf>NH<inf>3</inf>PbX<inf>3</inf> such as large absorption coefficients, long-lived free-carriers, and large carrier diffusion lengths are considered to be the reasons for the high solar-cell efficiencies [1]. In addition, CH<inf>3</inf>NH<inf>3</inf>PbX<inf>3</inf> perovskites show extremely high luminescence efficiencies and unique optical phenomena such as photon recycling (photoemission and reabsorption processes) recently discovered in CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf> [2] and CH<inf>3</inf>NH<inf>3</inf>PbBr<inf>3</inf> [3]. Photon recycling is a very important optical process determining the external quantum efficiencies of solar cells and light-emitting diodes. To achieve further improvements of performance in CH<inf>3</inf>NH<inf>3</inf>PbX<inf>3</inf>-based photonic device, the fundamental optical responses are needed to be clarified.

Free excitons and exciton-phonon coupling in CH 3 NH 3 PbI 3 perovskite single crystals at low temperatures

Hybrid lead halide perovskites, such as methylammonium lead halides CH3NH3PbX3 (MAPbX3, X = I, Br, Cl), are emerging as an excellent class of materials for various optoelectronic applications including solar cells, light-emitting diodes, lasers, and photodetectors [1,2]. As for these perovskite-based devices, deep understanding of transport properties of excitons and charge carriers in perovskite layer is essentially needed in order to achieve a better performance. Although the recombination dynamics in MAPbX3 materials have been investigated extensively [3,4], there are limited works devoted to elucidating the scattering processes of excitons and charge carriers with phonons and impurities. Thus far, the spectral width extracted from conventional photoluminescence (PL) spectroscopy has been used to examine the electron- and exciton-phonon interactions in perovskite polycrystalline thin films [5]. However, polycrystalline thin films consist of grains with various sizes and compositions; these lead to a broad inhomogeneous PL spectral width, and therefore, prevent an appropriate evaluation of the scattering processes. In addition, PL spectrum at low temperatures is composed of multiple emission bands [4,5] and usually dominated by the emission band from the bound excitons due to their giant oscillator strength. A precise extraction of the spectral width of the free-exciton emission band could not be obtained qualitatively based on only PL measurement at low temperatures. Here, we report a study of the free-exciton properties and the exciton-phonon interaction in orthorhombic-phase MAPbI3 single crystals by means of simultaneous temperature-dependent photocurrent (PC) and PL measurements.

Construction of push—pull systems using β-formyl-β-nitroenamine

The review is focused on the application of β-formyl-β-nitroenamines, one of the push—pull alkenes, having the biased electron density as well as an electrophilic formyl group and a nucleophilic amino group in the organic synthesis. Due to the multi-functionality, β-formyl-β-nitroenamines exhibit versatile reactivity to facilitate the synthesis of polyfunctionalized compounds possessing push—pull property. Nitroenamines serve as a synthetic equivalent of unstable nitromalonaldehyde to afford nitropyrazoles, nitropyrimidines, nitrodiazepines, and nitrophenoles upon treatment with dinucleophiles such as hydrazines, amidines, 1,2-diamines, and ketones, respectively. When active methylene compounds allowed reacting with the nitroenamines, polyfunctionalized pyridones and 2-amino-5-nitropyridines are obtained. In addition, nitroenamines undergo [4+2] self-condensation to afford 3,5-dinitropyridinium ion, which is easily trapped by benzene derivatives leading to 4-arylated 1,4-dihydropyridines.