Unraveling the Mechanisms of the Excited-State Intermolecular Proton Transfer (ESPT) for a D-π-A Molecular Architecture

Precise revealing the mechanisms of excited-state intermolecular proton transfer (ESPT) and the corresponding geometrical relaxation upon photoexcitation and photoionization remains a formidable challenge. In this work, the compound (E)-4-(((4H-1,2,4-triazol-4-yl)imino)methyl)-2,6-dimethoxyphenol (TIMDP) adopting a D-π-A molecular architecture featuring a significant intramolecular charge transfer (ICT) effect has been designed. With the presence of perchloric acid (35 %), TIMDP can be dissolved through the formation of a HClO₄–H₂O–OH(TIMDP)–N(TIMDP) hydrogen-bonding bridge. At the ground state, the ICT effect is dominant, giving birth to crystals of TIMDP. Upon external stimuli (e.g., UV light irradiation, electro field), the excited state is achieved, which weakens the ICT effect, and significantly promotes the ESPT effect along the hydrogen-bonding bridge, resulting in crystals of [HTIMDP]⁺ ⋅ [H₂O] ⋅ [ClO₄]⁻. As a consequence, the mechanisms of the ESPT can be investigated, which distorted the D-π-A molecular architecture, tuned the emission color with the largest Stokes shift of 242 nm, and finally, high photoluminescence quantum yields (12 %) and long fluorescence lifetimes (8.6 μs) have achieved. These results not only provide new insight into ESPT mechanisms, but also open a new avenue for the design of efficient ESPT emitters.     

Insights into the Control of Optoelectronic Properties in Mixed-Stacking Charge-Transfer Complexes

Although cocrystallization has provided a promising platform to develop new organic optoelectronic materials, it is still a big challenge to purposely design and achieve specific optoelectronic properties. Herein, a series of mixed-stacking cocrystals (TMFA, TMCA, and TMTQ) were designed and synthesized, and the regulatory effects of the acceptors on the co-assembly behavior, charge-transfer nature, energy-level structures, and optoelectronic characteristics were systematically investigated. The results demonstrate that it is feasible to achieve effective charge-transport tuning and photoresponse switching by carefully regulating the intermolecular charge transfer and energy orbitals. The inherent mechanisms underlying the change in these optoelectronic behaviors were analyzed in depth and elucidated to provide clear guidelines for future development of new optoelectronic materials. In addition, due to the excellent photoresponsive characteristics of TMCA, TMCA-based phototransistors were investigated with varying light wavelength and optical power, and TMCA shows the best performance among all reported cocrystals under UV illumination.     

Dual Emission from Precious Metal-Free Luminophores Consisting of C,H, O,Si, and S/P at Room Temperature

Fluorescence–phosphorescence dual-emissive compounds are valuable tools for ratiometric luminescence sensing. Herein, it is reported that 2,5-bis(phenylsulfonyl)- and 2,5-bis[bis(4-methoxyphenyl)phosphinyl]-1,4-disiloxybenzenes exhibit dual emission with emission peaks that were easily identified without performing time-gated measurement. The disiloxybenzenes in powder simultaneously fluoresced and phosphoresced at 358–374 and 457–470 nm, respectively, under vacuum. The intensity ratios of the phosphorescence/fluorescence maxima of the disiloxybenzenes in powder and in a thin film of poly(methyl methacrylate) were sensitive to temperature and molecular oxygen, respectively. The plots of the relative intensity versus temperature or partial pressure of molecular oxygen were well fitted with calibration curves defined by an exponential approximation with excellent correlation coefficients R² (0.9708–0.9921), demonstrating the high potential of the disiloxybenzenes as precious metal-free probes applicable to ratiometric luminescence sensing.     

Versatile coordination chemistry towards multifunctional carbon nanotube nanohybrids

Dispersible single-walled carbon nanotubes grafted with poly(4-vinylpyridine), SWNT-PVP, were tested in coordination assays with zinc tetraphenylporphyrin (ZnP). Kinetic and spectroscopic evidence corroborates the successful formation of a SWNT-PVPZnP nanohybrid. Within this SWNT-PVPZnP nanohybrid, static electron-transfer quenching (2.0+/-0.1) x 10(9) s(-1) converts the photoexcited-ZnP chromophore into a radical-ion-pair state with a microsecond lifetime, namely one-electron oxidized-ZnP and reduced-SWNT.     

Molecular assemblies from imidazolyl-containing haloalkenes and haloalkynes: competition between halogen and hydrogen bonding

The structural characterization of molecular assemblies constructed from imidazolyl-containing haloalkenes and haloalkynes is reported. 1-(3-Iodopropargyl)imidazole (2) and 1-(2,3,3-triiodoallyl)imidazole (5) were synthesized from 1-propargylimidazole (1). In the solid state, these wholly organic modules self-assemble through N...I halogen-bonding interactions, thus giving rise to polymeric chains. The N...I interaction observed in 2 (d(N...I)=2.717 A, angle-spherical C(sp)-I...N=175.8 degrees) is quite strong relative to previously reported data. The N...I interaction in 5 (d(N...I)=2.901 A, angle-spherical C(sp2)-I...N=173.6 degrees) is weaker, in accordance with the order C(sp)-X<--base>C(sp2)-X<--base. Compound 5 was found to give a 1:1 cocrystal 4 with morpholinium iodide (6). In the X-ray crystal studies of 4, N...I halogen-bonding interactions similar to those observed in 5 were shown not to be present, as the arrangement of the molecules is governed by two interwoven hydrogen-bonding networks. The first network involves N-H...O interactions between nearby morpholinium cations, and the second network is based on N-H...N hydrogen bonding between morpholinium cations and imidazolyl groups. Both hydrogen-bonding schemes are charge-assisted. Halogen bonding is not completely wiped out, however, as the triiodoalkene fragment forms a halogen bond with an iodide anion in its vicinity (d(I...I)=3.470 A, angle-spherical C(sp2)-I...I=170.7 degrees). X-ray crystal studies of 6 show a completely different arrangement from that observed in 4, namely, N-H...O interactions are not present. In crystalline 6, morpholinium cations are interconnected through C-H...O bridges (d(H...O)=2.521 and 2.676 A), and the NH2+ groups interact with nearby iodide anions (d(H...I)=2.633 and 2.698 A).     

(4R)-5,5-二甲基-4-苄硫甲基-2-噁唑烷酮的合成

以价廉易得的天然L-半胱氨酸为原料,经巯基保护、酯化、氨基保护、格氏反应及环化等5步反应,合成了一个新的手性助剂(4R)-5,5-二甲基-4-苄硫甲基-2-噁唑烷酮,总收率31%.产物结构经IR,~1H NMR,~(13)C NMR及MS表征.     

Boron Subphthalocyanines and Silicon Phthalocyanines for Use as Active Materials in Organic Photovoltaics

Organic photovoltaics (OPVs) have experienced continued interest over the last 25 years as a viable technology for the generation of power. Phthalocyanines are among the oldest commercial dyes and have been utilized in some of the earliest examples of OPVs. In recent years, the use of boron subphthalocyanines (BsubPcs) and silicon phthalocyanines (SiPcs) has attracted a flurry of interest with some examples of fullerene‐free devices reaching power conversion efficiencies >8 %. Unlike other more common divalent phthalocyanines such as copper or zinc, BsubPcs and SiPcs contain additional axial groups that can easily be functionalized without significantly affecting the optoelectronic properties of the macrocycle. This handle facilitates our ability to tune the solid‐state arrangement and other physical characteristics such as solubility ultimately giving us the ability to improve the thin film processing and final device performance. This review covers recent studies on the development of BsubPcs and SiPcs for use as active materials in organic photovoltaics.     

Kinetic Studies of Donor–Acceptor Cyclopropanes: The Influence of Structural and Electronic Properties on the Reactivity

The kinetics of (3+2) cycloaddition reactions of 18 different donor–acceptor cyclopropanes with the same aldehyde were studied by in situ NMR spectroscopy. Increasing the electron density of the donor residue accelerates the reaction by a factor of up to 50 compared to the standard system (donor group=phenyl), whereas electron‐withdrawing substituents slow down the reaction by a factor up to 660. This behavior is in agreement with the Hammett substituent parameter σ. The obtained rate constants from the (3+2) cycloadditions correlate well with data from additionally studied (3+n) cycloadditions with a nitrone (n=3) and an isobenzofuran (n=4). A comparison of the kinetic data with the bond lengths in the cyclopropane (obtained by X‐ray diffraction and computation), or the ¹H and ¹³C NMR shifts, revealed no correlation. However, the computed relaxed force constants of donor–acceptor cyclopropanes proved to be a good indicator for the reactivity of the three‐membered ring.     

Improved Synthesis of the ORL Antagonist 1-[(3R,4R)-1-Cyclooctylmethyl-3-ethoxycarbonyl-4-piperidinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397)

A practical synthesis of optically pure 1-[(3R,4R)-1-cyclooctylmethyl-3-ethoxycarbonyl-4-piperidinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397) was developed that avoids the use of chiral columns.