Hiroaki Imoto

Role of Solvent Dielectric Properties on Charge Transfer from PbS Nanocrystals to Molecules

Transfer of photoexcited charge from PbS nanocrystals to ligand molecules is investigated in different solvents. We find that the charge transfer rate increases dramatically with solvent dielectric constant. This trend is accounted for by a modified Marcus theory that incorporates only static dielectric effects. The choice of solvent allows significant control of the charge transfer process. As an important example, we find that PbS nanocrystals dispersed in water exhibit charge transfer rates 1000 times higher than the same nanocrystals in organic solvent. Rapid charge extraction will be important to efficient nanocrystal-based photovoltaic and photodetector devices.

para-Bisvinylhexaisobutyl-substituted T8 caged monomer: synthesis and hydrosilylation polymerization

The selective introduction of functional groups at the para-position in mono-functionalized T8-caged silsesquioxanes would enable us to design new organic inorganic hybrid polymers. Here, a para-substituted bisvinylhexaisobutyl-T8 caged monomer was successfully synthesized via a selective corner-opening reaction of the vinylheptaisobutyl-T8 cage followed by a subsequent corner-capping reaction.

Color Tuning of the Aggregation‐Induced Emission of Maleimide Dyes by Molecular Design and Morphology Control

Aggregation-induced emission (AIE)-active maleimide dyes, namely, 2-p-toluidino-N-p-tolylmaleimide, 3-phenyl-2-toluidino-N-p-tolylmaleimide, 2-p-thiocresyl-3-p-toluidino-N-p-tolylmaleimide, and 2,3-dithiocresyl-N-arylmaleimides, were synthesized by facile synthetic procedures. The dyes show intense emission in the solid state, and emission colors were controlled from green (λmax =527 nm) to orange (λmax =609 nm) by varying the substituents at the 2- and 3-positions of the maleimide and the packing structures in the solid state. 2,3-Disubstituted maleimide dyes effectively underwent redshifts of their emission wavelength. Furthermore, some of the dyes exhibited mechanochromism and polymorphism, and their emission properties were dramatically dependent on the morphology of the solid samples. The mechanisms of the emission behaviors were investigated by X-ray diffraction. The substituent of the nitrogen atom of the maleimide ring affected the intermolecular interactions and short contacts, which were observed by single crystal X-ray crystallography, to result in completely different emission properties.

Arsole-Containing π-Conjugated Polymer by the Post-Element-Transformation Technique

A synthetic method to obtain an arsole-containing π-conjugated polymer by the post-transformation of the organotitanium polymer titanacyclopentadiene-2,5-diyl unit with an arsenic-containing building block is described. The UV/Vis absorption maximum and onset of the polymer were observed at 517 nm and 612 nm, respectively. The polymer exhibits orange photoluminescence with an emission maximum (Emax ) of 600 nm and the quantum yield (Φ) of 0.05. The polymer proved to exhibit a quasi-reversible redox behavior in its cyclic voltammetric (CV) analysis. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated to be -5.43 and -3.24 eV, respectively, from the onsets for oxidation and reduction signals in the CV analysis. Further chemical modification of the arsole unit in the π-conjugated polymer by complexation of gold(I) chloride occurred smoothly resulting in the bathochromic shift of the UV/Vis absorption and lowering of the LUMO energy level.

Practical Synthesis and Properties of 2,5-Diarylarsoles

2,5-Diarylarsoles were easily synthesized from nonvolatile arsenic precursors. Diiodoarsine was generated in situ and reacted with titanacyclopentadienes to give 2,5-diarylarsoles. The structures and optical properties were studied in comparison with those of 2,5-diarylphosphole. It was found that the arsoles were much more stable in the air than the phosphole. Single crystal X-ray diffraction revealed the arsenic atoms adopted a trigonal pyramidal structure, reflecting on the s-character of the lone pair. The obtained 2,5-diarylarsoles and 2,5-diarylphosphole showed intense emission in solutions and solid state. In addition, the optical properties were controlled by transition-metal coordination.

Stereospecific Construction of a trans-1,4-Diphosphacyclohexane Skeleton

trans-1,4-Diphosphacyclohexanes were successfully synthesized by the stereospecific intramolecular coupling reaction of the optically active bisphosphine. This is a new route for the construction of the trans-1,4-diphosphacyclohexane skeleton. A cis isomer was also prepared along with the trans isomer from a mixture of rac- and meso-bisphosphines. The coordinated boranes were easily removed to afford the corresponding 1,4-diphosphacyclohexanes.

Effect of alkyl groups on emission properties of aggregation induced emission active N-alkyl arylaminomaleimide dyes

Aggregation induced emission (AIE) active N-alkyl aminomaleimide dyes with various kinds of N-alkyl groups were synthesized in a one pot process. The synthesized dyes exhibited different emission behaviors depending on the chemical structure of the N-alkyl group, although they had no direct contribution to the π-conjugated system. Chain length, hydroxyl group and branching structure were important in the emission properties such as quantum yield and emission wavelength. Furthermore, it was found that one of the dyes showed mechanochromism; the green emission of crystal samples turned to blue emission after grinding. Single crystal X-ray diffraction analysis revealed that the surrounding around the luminophore was dominant in the emission behaviors.

Synthesis and Properties of Oligophenylene-Layered Polymers

We report syntheses of phenylene-, biphenylene-, and terphenylene-layered polymers with a xanthene scaffold by the modified Suzuki-Miyaura coupling reaction. Their optical properties were studied in detail. The polymer end-capped by nitrobenzene units, which act as fluorescence quenchers, exhibited the photo-excited energy transfer from the layered oligophenylenes to the terminal units.

Synthesis of enantiomerically pure P-stereogenic diphosphacrowns and their palladium complexes.

A practical synthetic route for enantiomerically pure P-stereogenic diphosphacrowns was developed by using a P-stereogenic bisphosphine as a chiral building block. Their molecular structures were confirmed by NMR spectroscopy and X-ray crystallography. Complexation of the diphosphacrowns with palladium was carried out, and the corresponding palladium complexes were obtained. The P-stereogenic diphosphacrowns were applicable to the chiral ligand for the asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated ketone catalyzed by palladium. This reaction proceeded smoothly to afford the corresponding 1,4-addition products in high yield with good enantioselectivities.

Synthesis of Optically Active Polymer with P-Stereogenic Phosphine Units

Optically active polymer containing P-stereogenic bisphosphine as a repeating unit in the main was successfully synthesized. A coordinated borane on the phosphorus atom could be completely removed by an organic base under mild condition, and the successive reaction with Pd afforded the corresponding polymer complex. The chirality of P-stereogenic centers was transferred to the m-phenylene-ethynylene linkers by complexation because of the prohibition of the rotary motion of the bisphosphine-Pd unit.