Heterogeneous catalysis often involves molecular adsorptions to charged catalyst site and reactions triggered by catalyst charges. Here we use first-principles simulations to design oxygen reduction reaction (ORR) catalyst based on double transition metal (TM) atoms stably supported by 2D crystal C2N. It not only holds characters of low cost and high durability but also effectively accumulates surface polarization charges on TMs and later deliveries to adsorbed O2 molecule. The Co-Co, Ni-Ni, and Cu-Cu catalysts exhibit high adsorption energies and extremely low dissociation barriers for O2, as compared with their single-atom counterparts. Co-Co on C2N presents less than half the value of the reaction barrier of bulk Pt catalysts in the ORR rate-determining steps. These catalytic improvements are well explained by the dependences of charge polarization on various systems, which opens up a new strategy for optimizing TM catalytic performance with the least metal atoms on porous low-dimensional materials.

Based on DFT calculations, we propose a TM@CN hybrid structure, in which the single-atom transition metal (TM = Pt, Pd, Co, Ni, Cu) is supported by graphitic carbon nitride (g-CN), as a promising high-performance OER catalyst. Our work reveals the importance of local TM coordination in catalysts for the OER, which would lead to a new class of low-cost, durable and efficient OER catalysts.

We report the synthesis, photophysics, and reverse saturable absorption together with time-dependent density functional theory modeling of seven cationic iridium(III) complexes bearing one 2,2′-bipyridine ligand and two cyclometalating ligands (C^N ligand) with varied degrees of π-conjugation (HC^N = benzo[H]quinoline in 1, 1-phenylisoquinoline in 2, 1-(2-pyridyl)naphthalene in 3, 2-(2-pyridyl)naphthalene in 4, 1-(2-pyridyl)pyrene in 5, 1,2-diphenyl-pyreno[4,5-d]imidazole in 6, and 3-(2-pyridyl)perylene in 7). All complexes possess ligand-localized 1π,π* transitions as the major absorption bands and lower-energy 1MLCT (metal-to-ligand charge transfer)/1LLCT (ligand-to-ligand charge transfer) transitions in their ultraviolet–visible absorption spectra. The extended π-conjugation in the cyclometalating ligands of complexes 5–7 causes a significant red-shift of the major absorption bands with increased molar extinction coefficients with respect to those of complexes 1–4 that contain less conjugated C^N ligands. All complexes are emissive in solutions at room temperature and in glassy matrix at 77 K. The emitting states are assigned to 3π,π* (C^N ligand localized) /3MLCT for 1, 3π,π*/3MLCT/3LMCT (ligand-to-metal charge transfer) for 2–4, pure 3π,π* transitions for 5 and 6, and 3π,π*/3MLCT/3LMCT/3LLCT for 7. Complex 5 possesses the lowest emission energy because the larger conjugation and the most delocalized character of the 3π,π* transition within the C^N ligand in this complex. Complexes 1, 4, and 7 possess larger contribution of charge transfer characters in their lowest triplet excited states. Therefore, the transient absorption of these three complexes is broad but short-lived (90–300 ns). In contrast, complexes 2, 3, 5, and 6 all give long-lived (2.0–19.5 μs) triplet transient absorption in the visible spectral region of ca. 450–700 nm, which can be regarded as emanating predominantly from the C^N ligand-centered 3π,π* state. The reverse saturable absorption (RSA) of these complexes was evaluated at 532 nm for nanosecond laser pulses. The results demonstrate that these complexes, except for 7, all exhibit strong RSA for nanosecond laser pulses at 532 nm, with a trend of 7 < 1 < 4 < 6 < 5 ≈ 2 ≈ 3.

Thermodynamic conditions governing the charge transfer direction in CdSe quantum dots (QD) functionalized by either Ru(II)-trisbipyridine or black dye are studied using density functional theory (DFT) and time-dependent DFT (TDDFT). Compared to the energy offsets of the isolated QD and the dye, QD-dye interactions strongly stabilize dye orbitals with respect to the QD states, while the surface chemistry of the QD has a minor effect on the energy offsets. In all considered QD/dye composites, the dyes always introduce unoccupied states close to the edge of the conduction band and control the electron transfer. Negatively charged ligands and less polar solvents significantly destabilize the dye's occupied orbitals shifting them toward the very edge of the valence band, thus, providing favorite conditions for the hole transfer. Overall, variations in the dye's ligands and solvent polarity can progressively adjust the electronic structure of QD/dye composites to modify conditions for the directed charge transfer.

A critical issue in photodynamic therapy (PDT) is inadequate reactive oxygen species (ROS) generation in tumors, causing inevitable survival of tumor cells that usually results in tumor recurrence and metastasis. Existing photosensitizers frequently suffer from relatively low light‐to‐ROS conversion efficiency with far‐red/near‐infrared (NIR) light excitation due to low‐lying excited states that lead to rapid non‐radiative decays. Here, a neutral Ir(III) complex bearing distyryl boron dipyrromethene (BODIPY‐Ir) is reported to efficiently produce both ROS and hyperthermia upon far‐red light activation for potentiating in vivo tumor suppression through micellization of BODIPY‐Ir to form “Micelle‐Ir”. BODIPY‐Ir absorbs strongly at 550–750 nm with a band maximum at 685 nm, and possesses a long‐lived triplet excited state with sufficient non‐radiative decays. Upon micellization, BODIPY‐Ir forms J‐type aggregates within Micelle‐Ir, which boosts both singlet oxygen generation and the photothermal effect through the high molar extinction coefficient and amplification of light‐to‐ROS/heat conversion, causing severe cell apoptosis. Bifunctional Micelle‐Ir that accumulates in tumors completely destroys orthotopic 4T1 breast tumors via synergistic PDT/photothermal therapy (PTT) damage under light irradiation, and enables remarkable suppression of metastatic nodules in the lungs, together without significant dark cytotoxicity. The present study offers an emerging approach to develop far‐red/NIR photosensitizers toward potent cancer therapy.

Five heteroleptic cationic iridium complexes with a π-expansive cyclometalating 2,3-diphenylbenzo[g]quinoxaline (dpbq) ligand (C^N ligand) and different diimine ligands (N^N ligands) (i.e. 2,2'-bipyridine (bpy, 1), phenanthroline (phen, 2), 2-(2-pyridinyl)quinoline (pqu, 3), 2,2'-bisquinoline (bqu, 4), and 2-(quinolin-2-yl)quinoxaline (quqo, 5)) were synthesized and characterized. The lowest-energy singlet electronic transitions (S states) were mainly dpbq ligand-centred ILCT (intraligand charge transfer)/MLCT (metal to ligand charge transfer) transitions mixed with some π,π* transitions for complexes 1-4 with increased contributions fromLLCT (ligand to ligand charge transfer) in 3 and 4. For complex 5, the S state was switched to the LLCT/MLCT transitions. All five complexes displayed weak near-infrared (NIR) phosphorescence, with maximal emission output spanning 700-1400 nm and quantum yields being on the order of 10. The triplet state absorptions of 1-4 all resembled that of the [Ir(dpbq)Cl] dimer with lifetimes of ca. 400 ns, while the TA spectrum of 5 possessed the characteristics of both the quqo ligand and the [Ir(dpbq)Cl] dimer with a bi-exponential decay of ca. 5 μs and 400 ns. While the photophysics of these complexes differ slightly, their theranostic photodynamic therapy (PDT) effects varied drastically. All of the complexes were biologically active toward melanoma cells. Complexes 2 and 3 were the most cytotoxic, with 230-340 nM activity and selectivity factors for melanoma cells over normal skin fibroblasts of 34 to 40 fold. Complexes 2, 3, and 5 became very potent cytotoxins with light activation, with EC values as low as 12-18 nM. This potent nanomolar light-triggered activity combined with a lower dark toxicity resulted in 5 having a phototherapeutic index (PI) margin of almost 275. The bpy coligand led to the least amount of dark toxicity of 1, while phen and pqu produced cytotoxic but selective complexes 2 and 3. The quqo coligand produced the most potent complex 5 for in vitro PDT, both in terms of photocytotoxicity and PI. All Ir(iii) complexes exhibited very bright NIR phosphorescence in melanoma cells. The wide range of cytotoxicity and photocytotoxicity effects within a relatively small class of complexes highlights the importance of the identity of the coligand in the biological activity of the π-expansive biscyclometalated Ir(iii) complexes, and their bright NIR emission in live cells demonstrates their potential as theranostic PDT agents.

Iridium(iii) complexes bearing the 2-(2-quinolinyl)quinoxaline ligand absorb weakly at 450–750 nm and can be used as broadband reverse saturable absorbers.

We here report an efficient and enhanced fluorescence energy transfer system between confined quantum dots (QDs) by entrapping CdTe into the mesoporous silica shell (CdTe@SiO₂) as donors and gold nanoparticles (AuNPs) as acceptors. At pH 6.50, the CdTe@SiO₂-AuNPs assemblies coalesce to form larger clusters due to charge neutralization, leading to the fluorescence quenching of CdTe@SiO₂ as a result of energy transfer. As compared with the energy transfer system between unconfined CdTe and AuNPs, the maximum fluorescence quenching efficiency of the proposed system is improved by about 27.0%, and the quenching constant, K(sv), is increased by about 2.4-fold. The enhanced quenching effect largely turns off the fluorescence of CdTe@SiO₂ and provides an optimal "off-state" for sensitive "turn-on" assay. In the present study, upon addition of melamine, the weak fluorescence system of CdTe@SiO₂-AuNPs is enhanced due to the strong interactions between the amino group of melamine and the gold nanoparticles via covalent bond, leading to the release of AuNPs from the surfaces of CdTe@SiO₂; thus, its fluorescence is restored. A "turn-on" fluorimetric method for the detection of melamine is proposed based on the restored fluorescence of the system. Under the optimal conditions, the fluorescence enhanced efficiency shows a linear function against the melamine concentrations ranging from 7.5 × 10⁻⁹ to 3.5 × 10⁻⁷ M (i.e., 1.0-44 ppb). The analytical sensitivity is improved by about 50%, and the detection limit is decreased by 5.0-fold, as compared with the analytical results using the CdTe-AuNPs system. Moreover, the proposed method was successfully applied to the determination of melamine in real samples with excellent recoveries in the range from 97.4 to 104.1%. Such a fluorescence energy transfer system between confined QDs and AuNPs may pave a new way for designing chemo/biosensing.