Charge Transfer Emission of T‑Shaped π‑Conjugated Molecules: Impact of Quinoid Character on the Excited State Properties

We investigate the impact of quinoid character of a π-conjugation system on the emission properties of T-shaped cross-conjugated molecules. Three π-conjugated systems with different quinoid nature including benzothiophene, 2-phenylthiophene, and 2-phenylthieno­[3,2-<i>b</i>]­thiophene were connected orthogonally to a π-conjugated bis­(phenylethynyl)­arylene with an acid responsive <i>N</i>-methylbenzimidazole junction. The enhancement of quinoid character of a vertical π-system effectively suppressed the twisted intramolecular charge transfer (TICT) emission, leading to a more planar ICT state with enhanced emission intensity as well as a shortened Stokes shift

Photophysical Properties of a Terarylene Photoswitch with a Donor–Acceptor Conjugated Bridging Unit

A terarylene photoswitch composed of an electron-donating thienothiophene unit which is connected to the central bridging imidazole was designed. The electronic and geometrical structures of the central π-conjugation unit was controlled by chemical modifications on the imidazole unit, in which the distribution of frontier molecular orbitals was modulated between the neutral state and its protonated or quaternized cationic forms. These electronic and geometrical changes modulated the mixing of the closely lying excited state potential energy surfaces, resulting in the excitation wavelength dependent photocyclization performance. The chemical modifications on the imidazole ring also had an effect on the fluorescence property in the open-ring forms, which is explained by the formation of different push–pull π-conjugation systems

Circularly Polarized Luminescence in Chiral Aggregates: Dependence of Morphology on Luminescence Dissymmetry

The self-assembly of a chiral perylene bisimide bichromophoric derivative possessing a 1,1′-binaphthalene bridge was investigated by adopting two different methodologies, leading to the formation of aggregates with dissimilar morphologies. The chiral nature of the aggregated structures was optically probed with the help of circular dichroism (CD), vibrational circular dichroism (VCD), and circularly polarized luminescence (CPL). The one-dimensional aggregates formed in methylcyclohexane (MCH) exhibited twice the value of luminescence dissymmetry factor (<i>g</i>_lum) when compared with the spherical aggregates formed in chloroform at higher concentration. The summation of excitonic couplings between the individual chromophoric units in an aggregated system is responsible for the remarkably high luminescence dissymmetry exhibited by the chiral aggregates. The nanostructures could be successfully embedded into polymer films, leading to the fabrication of solid-state materials with high CPL dissymmetry that can find novel applications in chiroptical sensing, memory, and light-emitting devices based on organic nanoparticles

Circularly Polarized Luminescence in Chiral Aggregates: Dependence of Morphology on Luminescence Dissymmetry

The self-assembly of a chiral perylene bisimide bichromophoric derivative possessing a 1,1′-binaphthalene bridge was investigated by adopting two different methodologies, leading to the formation of aggregates with dissimilar morphologies. The chiral nature of the aggregated structures was optically probed with the help of circular dichroism (CD), vibrational circular dichroism (VCD), and circularly polarized luminescence (CPL). The one-dimensional aggregates formed in methylcyclohexane (MCH) exhibited twice the value of luminescence dissymmetry factor (<i>g</i>_lum) when compared with the spherical aggregates formed in chloroform at higher concentration. The summation of excitonic couplings between the individual chromophoric units in an aggregated system is responsible for the remarkably high luminescence dissymmetry exhibited by the chiral aggregates. The nanostructures could be successfully embedded into polymer films, leading to the fabrication of solid-state materials with high CPL dissymmetry that can find novel applications in chiroptical sensing, memory, and light-emitting devices based on organic nanoparticles

Synthesis and Photophysical Properties of a 13,13′-Bibenzo[<i>b</i>]perylenyl Derivative as a π‑Extended 1,1′-Binaphthyl Analog

A 13,13′-bibenzo­[<i>b</i>]­perylenyl derivativean axially chiral π-extended compound in which two perylene subunits fused to 1,1′-binaphthyl scaffoldhas been synthesized from 1,8-dibromo­phenanthrene using an anionic cyclodehydrogenation reaction in the presence of potassium metal as the key step. The pair of enantiomers can be separated by chiral high-performance liquid chromatography (HPLC), which showed a strong circular dichroism (CD) (Δε = 330 M^–1 cm^–1 at 449 nm, |<i>g</i>_CD| = 5.8 × 10^–3 at 453 nm), high fluorescence quantum yield (Φ_f = 64%), and strong circular polarized luminescence (CPL) (|<i>g</i>_CPL| = 5 × 10^–3 at 454 nm) in solution phase

Photocatalytic CO₂ Reduction to Formic Acid Using a Ru(II)–Re(I) Supramolecular Complex in an Aqueous Solution

In an aqueous solution, photophysical, photochemical, and photocatalytic abilities of a Ru­(II)–Re­(I) binuclear complex (<b>RuReCl</b>), of which Ru­(II) photosensitizer and Re­(I) catalyst units were connected with a bridging ligand, have been investigated in details. <b>RuReCl</b> could photocatalyze CO₂ reduction using ascorbate as an electron donor, even in an aqueous solution. The main product of the photocatalytic reaction was formic acid in the aqueous solution; this is very different in product distribution from that in a dimethylformamide (DMF) and triethanolamine (TEOA) mixed solution in which the main product was CO. A ¹³CO₂ labeling experiment clearly showed that formic acid was produced from CO₂. The turnover number and selectivity of the formic acid production were 25 and 83%, respectively. The quantum yield of the formic acid formation was 0.2%, which was much lower, compared to that in the DMF–TEOA mixed solution. Detail studies of the photochemical electron-transfer process showed back-electron transfer from the one-electron-reduced species (OERS) of the photosensitizer unit to an oxidized ascorbate efficiently proceeded, and this should be one of the main reasons why the photocatalytic efficiency was lower in the aqueous solution. In the aqueous solution, ligand substitution of the Ru­(II) photosensitizer unit proceeded during the photocatalytic reaction, which was a main deactivation process of the photocatalytic reaction. The product of the ligand substitution was a Ru­(II) bisdiimine complex or complexes with ascorbate as a ligand or ligands

Synthesis and Photophysical Properties of a 13,13′-Bibenzo[<i>b</i>]perylenyl Derivative as a π‑Extended 1,1′-Binaphthyl Analog

A 13,13′-bibenzo­[<i>b</i>]­perylenyl derivativean axially chiral π-extended compound in which two perylene subunits fused to 1,1′-binaphthyl scaffoldhas been synthesized from 1,8-dibromo­phenanthrene using an anionic cyclodehydrogenation reaction in the presence of potassium metal as the key step. The pair of enantiomers can be separated by chiral high-performance liquid chromatography (HPLC), which showed a strong circular dichroism (CD) (Δε = 330 M^–1 cm^–1 at 449 nm, |<i>g</i>_CD| = 5.8 × 10^–3 at 453 nm), high fluorescence quantum yield (Φ_f = 64%), and strong circular polarized luminescence (CPL) (|<i>g</i>_CPL| = 5 × 10^–3 at 454 nm) in solution phase

Impact of Optical Purity on the Light Harvesting Property in Supramolecular Nanofibers

Supramolecular ordering and orientation of chromophores are tremendously accomplished in photosynthetic light harvesting complexes, which are crucial for long-range transfer of collected solar energy. We herein demonstrate the importance of optical purity on the organization of chromophoric chiral molecules for efficient energy migration. Enantiomeric bichromophoric compounds, which self-assemble into nanofibers capable of chiral recognition, were mixed to form supramolecular coassemblies with variable enantiopurity. The chiral molecules self-assembled into extended fibers regardless of enantiopurity, while their morphology was dependent on the enantiomeric excess. The optical purity of assemblies also had an effect on the emission efficiency; the nanofibers with higher enantiomeric excess afforded a larger emission quantum yield. The presence of an opposite enantiomer is considered to deteriorate the chiral molecular packing suitable for directional growth of the nanofiber, efficient exciton migration, and chiral guest recognition

Hierarchical Emergence and Dynamic Control of Chirality in a Photoresponsive Dinuclear Complex

Chiroptical photoswitches are of interest from a viewpoint of applications in advanced information technologies. We report dynamic on–off photoswitching of circularly polarized luminescence (CPL) in a binuclear europium complex system. Two coordination units are arranged closely in a chiral fashion by a photoresponsive ligand with a one-handed helical structure. The chirality in the helical scaffold is hierarchically transferred to the chirality in nine-coordinate complex sites. The chiral close arrangement of complex units induces the enrichment of a specific chiral coordination structure in the nine-coordinate europium sites. The chiral arrangement of complex units is switched in conjunction with the photoinduced helix–nonhelix structural change in the photoresponsive framework, demonstrating on–off switching of CPL with high contrast

Hierarchical Emergence and Dynamic Control of Chirality in a Photoresponsive Dinuclear Complex

Chiroptical photoswitches are of interest from a viewpoint of applications in advanced information technologies. We report dynamic on–off photoswitching of circularly polarized luminescence (CPL) in a binuclear europium complex system. Two coordination units are arranged closely in a chiral fashion by a photoresponsive ligand with a one-handed helical structure. The chirality in the helical scaffold is hierarchically transferred to the chirality in nine-coordinate complex sites. The chiral close arrangement of complex units induces the enrichment of a specific chiral coordination structure in the nine-coordinate europium sites. The chiral arrangement of complex units is switched in conjunction with the photoinduced helix–nonhelix structural change in the photoresponsive framework, demonstrating on–off switching of CPL with high contrast