Satoshi Takeuchi

ABSTRACT Optically active 2‐azatriptycene 1 bearing a 1‐pyrenyl unit was synthesized. The resolved enantiomers exhibited blue circularly polarized luminescence (CPL) in solution, with dissymmetry factor g _lum on the order of 10 ⁻⁴ –10 ⁻⁵ _. In contrast, the corresponding protonated species 1H ⁺ exhibited green CPL with reversed sign, demonstrating that optically active 2‐azatriptycene functions as an acid‐responsive chiral switching unit.

Vibrational chiroptical spectroscopy is a valuable tool for investigating the three-dimensional structure of various biomolecules, such as proteins and nucleic acids, in the solution phase. Since the functions of these biomolecules are closely related to their dynamic behavior, the extension of vibrational chiroptical spectroscopy to time-resolved measurements is a promising approach for elucidating the mechanisms responsible for biological functions. However, the implementation of vibrational chiroptical spectroscopy with an ultrashort pulsed laser source—a crucial step toward time-resolved chiroptical spectroscopy—presents significant technical challenges due to its inherently low signal intensity and the difficulty of precise polarization control. Here, we report a sensitive and effective method to measure vibrational Raman optical activity (ROA) spectra using sub-10-fs pulses, which we call time-domain Raman optical activity (TD-ROA) spectroscopy. Specifically, ROA spectra were obtained by measuring a time-dependent change in circular birefringence accompanied by coherent nuclear wavepacket motion. We performed proof-of-principle TD-ROA measurements with (+)- and (−)- β -pinene in the spectral range from 400 to 1200cm ⁻¹ , which shows the capability of the method to discriminate enantiomers. Our approach paves the way for tracking chiral nuclear motion that is correlated to the activation of various biomolecular functions.

A series of organic crystalline solids is prepared by Lewis pairing the pyridyl derivatives of benzothienobenzothiophene (BTBT) and tris(pentafluorophenyl)borane (TPFB). The Lewis pair series shows structural variations in the arrangements of the BTBT moiety: 1D π‐stacked columns covered by TPFB, slipped columns, and cofacial dimers. Quantum chemical calculations are performed to quantify the intermolecular electronic coupling and bandgaps, which reveal that the 1D columns are electronically fragmented at the dimer or tetramer level. In response to the degree of electronic aggregations, the Lewis pairs exhibit red‐shifted fluorescence, reaching 5810 cm⁻¹ from the emission maximum of the non‐substituted BTBT (397 nm) to that of one crystal form (516 nm). Scanning tunneling microscopy reveals that one Lewis pair is loosely gathered on the Ag(111) surface without any ordered arrangement of the adsorbates, differing from that in the solid phase. Furthermore, vibrational fingerprinting of the Lewis pair is achieved using tip‐enhanced Raman scattering techniques at the single‐molecule level, including the B–N and C–S stretching characteristics. These results provide insight into modulating the molecular arrangements of small‐molecule semiconducting units to alter the emission properties, as well as fabricating molecular devices adsorbed on surfaces via post‐modification.

Abstract Organic chromophores have been recognized for their ability to participate in photoinduced electron transfer processes and have attracted considerable attention as organic photoredox catalysts. Design of absorption band and redox potentials in organic photoredox catalysts is critical for providing the visible light-mediated transformation. Here, we disclose photochemical properties and reactivities of 2,7-diazapyrene boron complexes and their use as organic photoredox catalysts.