Aarzoo

We report the synthesis, characterization, and catalytic activity of two new palladium­(II) complexes featuring benzo­[d]­oxazol-2-yl-based pincer ligands, namely, [Pd­(NNN^mor)­Cl] (C1) [Pd­(NNN^pic)­Cl] (C2), and (where NNN^mor = N-(2-(benzo­[d]­oxazol-2-yl)­phenyl)-2-morpholinoacetamide) NNN^pic = N-(2-(benzo­[d]­oxazol-2-yl)­phenyl) picolinamide. Structures of the ligands and the complexes were confirmed by FTIR, NMR and high-resolution mass spectrometry (HRMS). Further, the molecular structure of C2 in the solid state was confirmed by single-crystal X-ray diffraction. The complex showed pincer coordination mode with a distorted square planar geometry. The catalytic activity of these Pd­(II) complexes in the direct arylation of indazoles and other heteroarenes with aryl bromides has been explored, with complex C2 exhibiting better reactivity compared to complex C1. Mechanistic investigations revealed that the catalytic pathway involves a Pd^II–Pd^IV-Pd^II cycle. The results are supported by DFT calculations.

Aggregation-induced emission (AIE) has emerged as a groundbreaking advancement in the field of photoluminescence behavior. A thorough understanding of the AIE mechanism is essential for the rational design of innovative molecules exhibiting these exceptional properties. In this study, we report a quantum mechanical (QM) investigation through spin-flip time dependent density functional theory (SF-TDDFT) using optimally tuned range-separated hybrid (OT-RSH) functional to explore the cause of fluorescence quenching of the ethylene derivatives such as TPE-9CB, TPE-3CB, and tetraphenylethene-triphenylamine in tetrahydrofuran (THF) solution. The fluorescence enhancement in the crystalline state of an ethylene derivative TPE-9CB is studied by adopting a QM:MM based approach using the SF-TDDFT method and RSH functional. It is observed that the OT-RSH functional delivers impressive results regarding photophysical properties. The twisting of the central C=C bond has been identified as the phenomenon that quenches the photoexcited state of the ethylene derivatives in THF solution. Notably, the minimum-gap point (MGP) along the α-torsional coordinate of the S1 state in solution lies ∼0.1 eV below the Frank–Condon (FC) point for all the derivatives. Interestingly, all examined monomers exhibited nearly zero oscillator strength (f values) near the point of minimum-gap, indicating minimal radiative transitions in the solution state. Conversely, the excited state deactivation channels, which involve the twisting of the central C=C bond in the solution phase, are effectively restricted in the solid state by steric hindrance and electrostatic repulsion from the neighboring molecules. In the solid state, the MGP is 0.48 eV above the FC point, demanding high energy to prevent photoinduced rotary relaxation. This effectively blocks nonradiative deactivation pathways, resulting in a significant enhancement of the emission response. Our findings underscore the potential of AIE phenomena in advancing material design and applications.

This study explores the mechanism of aggregation‐induced emission (AIE) in the tetrabenzoheptafulvalene derivative, 10,10′,11,11′‐tetrahydro‐5,5′‐bidibenzo[a,d][7]annulenylidene (abbreviated as THBDBA) in tetrahydrofuran (THF) solution. THBDBA is AIE‐active because in THF solution, it emits significantly less emission (or almost non‐emissive) and the fluorescence quantum yield increases by 230 times in aggregate state. We adopted spin‐flip time‐dependent density functional theory (SF‐TDDFT), widely acknowledged for its ability to locate the conical intersection (CI) in medium to large‐sized molecules (due to its balanced and reliable description of both ground and excited states and ability to capture double excitation and multireference characters at low computational cost). The functional used is long‐range corrected ωPBEh (i. e., LRC‐ωPBEh). The strategies used are the excited state deactivation processes by taking into account the S₁/S₀ surface crossing, referred to as the ‘minimum energy conical intersection’ (MECI). Reduction of oscillator strength near the minimum energy gap (MEG) structure or CI is also another parameter used to study fluorescence quenching. For the monomer (i. e., in solution), our findings reveal a significant reduction in oscillator strength (f) for de‐excitation near the MEG structure and CI, which led us to conclude that in solution, the flapping motion of the phenyl rings plays a vital role to reach the CI. In a smaller scale, a dimer system was chosen to represent the aggregate state. The higher energy gap as well as higher f‐value at MEG structure with just the model dimer system indicates that in the actual aggregate (or the crystal) the MECI might be absent. This is because in the aggregate the flapping motion of the phenyl rings will be highly restricted (because of the steric and electrostatic confinements by a large number of monomers from all sides), thereby favoring radiative transitions for energy dissipation. This study consequently elucidates the AIE mechanism of the chosen tetrabenzoheptafulvalene derivative, shedding light on its photophysical properties.