Comparison between SiMe2 and CMe2 Spacers as σ-Bridges for Photoinduced Charge Transfer

Discovery of Apararenone (MT-3995) as a Highly Selective, Potent, and Novel Nonsteroidal Mineralocorticoid Receptor Antagonist

Overactivation of the mineralocorticoid receptor (MR) is involved in many diseases, such as hypertension, kidney disease, and heart failure. Thus, MR antagonists (MRAs) are expected to be beneficial to patients with these diseases. In order to identify novel nonsteroidal MRAs that overcome the issues of already marketed steroidal MRAs, we searched for new compounds guided by our hypothesis that T-shaped compounds with a hydrophobic core structure, two polar functional groups at both extremities able to interact with MR, and a bulky substituent that can interfere with the folding of the C-terminal helix 12 may exhibit antagonist activity toward MR. We discovered that the novel 1,4-benzoxazin-3-one derivative 19 (apararenone: MT-3995) acted as a highly selective and potent nonsteroidal MRA. Apararenone exhibited a more potent antihypertensive and organ-protective activity than steroidal MRA eplerenone in a primary aldosteronism rat model obtained by infusing aldosterone in uninephrectomized rats.

C-N Bond Rotation Controls Photoinduced Electron Transfer in an Aminostyrene-Stilbene Donor-Acceptor System

We investigate energy transfer and electron transfer in a dimethylsilylene-spaced aminostyrene-stilbene donor-acceptor dimer using time-dependent density functional theory calculations. Our results confirm that the vertical S₃, S₂, and S₁ excited states are, respectively, a local excitation on the aminostyrene, local excitation on the stilbene, and the charge-transferred (CT) excited state with electron transfer from aminostyrene to stilbene. In addition, an energy minimum with the C-N bond of the amino group twisted at about 90° is also identified on the S₁ potential energy surface. This S₁ state exhibits a twisted intramolecular charge transfer (TICT) character. A potential energy scan along the C-N bond torsional angle reveals a conical intersection between the S₂ stilbene local excitation and the S₁ CT/TICT state at a torsional angle of ∼60°. We thus propose that the conical intersection dominates the electron transfer dynamics in the donor-acceptor dimer and copolymers alike, and the energy barrier along the C-N bond rotation controls the efficiency of such a process. Moreover, we show that despite the zero oscillator strength of the S₁ excited states in the CT and TICT minima, an emissive S₁ state with a V-shaped conformational structure can be located. The energy of this V-shape CT structure is thermally accessible; therefore, it is expected to be responsible for the CT emission band of the dimer observed in polar solvents. Our data provide a clear explanation of the complex solvent-dependent dual emission and photoinduced electron transfer properties observed experimentally in the dimer and copolymer systems. More importantly, the identifications of the conical intersection and energy barrier along the C-N bond rotation provide a novel synthetic route for controlling emissive properties and electron transfer dynamics in similar systems, which might be useful in the design of novel organic optoelectronic materials.

Donor-σ-Acceptor Motifs: Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion

A family of organic emitters with a donor-σ-acceptor (D-σ-A) motif is presented. Owing to the weakly coupled D-σ-A intramolecular charge-transfer state, a transition from the localized excited triplet state (³ LE) and charge-transfer triplet state (³ CT) to the charge-transfer singlet state (¹ CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200-400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D-σ-A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes.

Electron transfer in silicon-bridged adjacent chromophores: the source for blue-green emission

Electron transfer between adjacent chromophores (N-isopropylcarbazole and divinylbenzene) through a silylene bridge is the source for blue-green emission.

Unusual emission properties of the selected organosilicon compounds containing a styryl-carbazole chromophore: inversion of the singlet excited states

The presence of the silicon atom in a trimethylsilyl-styryl-carbazole derivative induced the inversion of the lowest excited states in polar solvents.

Metal Ion Enhanced Charge Transfer in a Terpyridine-bis-Pyrene System

The synthesis, electrochemical and photophysical properties of a branched molecule 3,5-bis(pyrene-1-yl)-4'-phenyl-2,2':6',2″-terpyridine are reported. Spectroscopy in different solvents reveals that an optical electron transfer from the pyrene donor to the terpyridyl electron acceptor can occur in polar media, as the system displays both charge transfer (CT) absorption and CT emission. Furthermore, the study of the zinc complex as well as the bis-protonated form shows an enhancement of the electron transfer character of the system, by an increase of the acceptor strength. This is accompanied by a large increase of the non-radiative processes. With sub-nanosecond transient absorption spectroscopy, the CT state, consisting of the pyrene radical cation and the terpyridine radical anion, has been detected. At room temperature, the study of the nanosecond transient absorption spectra reveals the formation of a low-lying triplet excited state that we attribute to the pyrene moiety through which the CT state decays. At 77K, the absence of the terpyridine triplet emission also suggests the population of a low-lying triplet state of the pyrene unit.

Synthesis and Spectroscopic Studies of Arylethynylsilanes

A variety of arylethynylsilanes (Ar-C[triple bond]C-C6H4-C[triple bond]C)(n)SiMe(4-n) were prepared successfully by reaction of the corresponding chlorosilanes Me(4-n)SiCl(n) with Ar-C[triple bond]C-C6H4-C[triple bond]CM (M = Li, MgBr), which was prepared by treatment of ethynyl(diarylethyne)s Ar-C[triple bond]C-C6H4-C[triple bond]CH with BuLi or MeMgBr. The ethynyl(diarylethyne)s were readily prepared in good yields by the double-elimination method: addition of lithium hexamethyldisilazide to a mixture of ArCH2SO2Ph, TMS-C[triple bond]C-C6H4-CHO, and ClP(O)(OEt)2, followed by desilylation. In the tetrakis(arylethynyl)silanes (Ar-C[triple bond]C-C6H4-C[triple bond]C)4Si thus prepared, through-space conjugation of four triple bonds on the silicon atom emerges as a result of participation of the silicon orbitals in the acetylenic pi orbitals. This participation enhances the emissive quantum yields of arylethynylsilanes with an increase in the number of arylethynyl moieties on silicon: quantum yields of emission (phiF) of 0.72 for (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C)4Si, 0.53 for (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C)2SiMe2, and 0.47 for MeO-C6H4-C[triple bond]C-C6H4-C[triple bond]CSiMe3 were obtained. Although this enhancement effect was also observed in the phenylethynylarylsilane (MeOC6H4-C[triple bond]C-C6H4)2SiMe2, the bis(arylethynyl)disilane (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C-SiMe2)2 exhibited non-enhanced emission.

Push-pull bithienyl chromophore with an unusual transverse path of conjugation

The synthesis, structure, and electronic properties of a novel cross-conjugated 10H-bisthienodithiocin-10-dicyanoethylene are reported. The X-ray single-crystal structure of the compound reveals a nonplanar conformation. The FT-IR and FT-Raman spectra of the compound show a great resemblance, which is a spectroscopic observation common to many push-pull systems. The UV-vis spectrum in CHCl3 displays a strong absorption at 370 nm accompanied by a shoulder at 430 nm so that the optical gap is 2.88 eV. On the other hand, the electrochemical gap amounts to 2.38 V. DFT and TDDFT quantum chemical calculations, at the B3LYP/6-31G** level, have been also performed to (i) determine the minimum-energy molecular structure, (ii) gain knowledge about the equilibrium atomic charges distribution, the topologies, and absolute energies of the frontier molecular orbitals around the gap and about the molecular vibrations which give rise to the most outstanding Raman bands experimentally evidenced, and (iii) to analyze the nature of the vertical one-electron excitations associated to the strongest UV-vis absorptions.

Alternating divinylarene–silylene copolymers

A summary of recent advances on the chemistry and photophysics of silylene-spaced divinylarene copolymers is presented. The silicon moieties have been shown to serve as an insulating spacer in these copolymers. The photophysical studies have provided useful insights into how chromophores in polymers interact intramolecularly. Because different chromophores can be regioregularly introduced into the polymeric chain, these copolymers have been extensively used as models for studying energy transfer, light harvesting as well as chiroptical transfer.

Synthesis, Light-Harvesting and Energy-Transfer Properties of Regioregular Silylene-Spaced Alternating [(Donor-SiMe2-)n=1-3-(Acceptor-SiMe2)] Copolymers

A series of silylene-spaced alternating [(donor-SiMe2)(n=1-3)-(acceptor-SiMe2)] copolymers 4-6 was synthesized by rhodium-catalyzed hydrosilylation of bisalkynes with bissilyl hydrides. Monomeric reference compounds 7-10 with similar chromophore components were prepared for comparison. The ratio of donor to acceptor groups is well-controlled by the precise regiochemistry and nature of the repeat units. The silylene moieties serve as insulating spacers between chromophores. The polymers exhibit light-harvesting abilities, for which the intensity of the emission enhanced with larger donor-to-acceptor ratios. No emission originating from the donors was observed in fluorescence spectra, illustrating that intrachain energy transfer is highly efficient along the polymer chain.

Photoinduced charge separation in a donor–acceptor functionalized 2,3-diphenylbutadiene: charge transport over a doubly bifurcated π-spacer

By studying photoinduced charge transfer processes in 2-(4-cyanophenyl)-3-(4-N,N-dimethylaminophenyl)-1,3-butadiene it is shown that insertion of branching points in a pi-conjugated pathway has a relatively small effect on the donor-acceptor interaction.

Synthesis of phenylnitroxides bridged by an sp(3)-linkage

Silicon- and carbon-bridged phenylnitroxides were synthesized. They exhibited similar ESR profiles independent of the nature of the sp(3) bridge and the substitution mode of the phenylene units. The spectra revealed a quintet signal at room temperature, which became a broad triplet by lowering the temperature. Accumulated ESR measurements at 77 K led to the successful observation of a signal at Deltam(s) = 2, indicating that the triplet state was involved in this system.