Four new heteroleptic cationic Ir(III) complexes bearing benzothiazolylfluorene motif on the bipyridine (N∧N) (1 and 2) and phenylpyridine (C∧N) (3 and 4) ligands are synthesized and characterized. The influence of the position of the substituent and the extent of π-conjugation on the photophysics of these complexes is systematically investigated by spectroscopic methods and simulated by time-dependent density functional theory (TDDFT). The complexes exhibit ligand-centered (1)π,π* transitions with admixtures of (1)ILCT (π(benzothiazolylfluorene) → π*(bpy)) and (1)MLCT (metal-to-ligand charge transfer) characters below 475 nm, and very weak (1,3)MLCT and (1,3)LLCT (ligand-to-ligand charge transfer) transitions above 475 nm. The emission of these complexes at room temperature in CH2Cl2 solutions is ascribed to be predominantly from the (3)MLCT/(3)LLCT states for 1 and from the (3)π,π* state for 2, while the emitting state of 3 and 4 are assigned to be an admixture of (3)MLCT, (3)LLCT, and (3)π,π* characters. The variations of the photophysical properties of 1-4 are attributed to different degrees of π-conjugation in the bipyridine and phenylpyridine ligands induced by different positions of the benzothiazolylfluorenyl substituents on the bipyridine ligand and different extents of π-conjugation in the phenylpyridine ligands, which alters the energy and lifetime of the lowest singlet and triplet excited states. 1-4 all possess broadband transient absorption (TA) upon nanosecond laser excitation, which extends from the visible to the NIR region. Therefore, 1-4 all exhibit strong reverse saturable absorption (RSA) at 532 nm for ns laser pulses. However, the TA of complexes 1, 2, and 3 are much stronger than that of 4. This feature, combined with the difference in ground-state absorption and triplet excited-state quantum yield, result in the difference in RSA strength, which follows this trend: 1 ≈ 2 ≈ 3 > 4. Therefore, complexes 1-3 are strong reverse saturable absorbers at 532 nm and could potentially be used as broadband nonlinear absorbing materials.

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Single- and few-layer α-M2X3 nanosheets exhibit out-of-plane SHG and piezoelectric properties, which can be tuned by switching spontaneous polarizations.

We report the superconductivity of CaSn3 single crystals with a AuCu3-type structure, namely cubic space group Pm3̄m.

(e.g., lower laser damage thresholds or two-photon absorption) that limit its applications. Therefore, it is important to develop new IR materials with large nonlinear susceptibility and high laser damage threshold, which impelled the recent exploration of many potential IR NLO chalcogenides, [ 5 ] halogenides, [6] and iodates. [7] However, these two parameters are usually correlated and contradictory: the wider the bandgap is, the higher the laser damage threshold, and the smaller the nonlinear susceptibility. This makes the discovery of effective NLO materials great diffi cult.We focus on the design and exploration of NLO materials, especially the propertyoriented design synthesis and the adjustment of property via crystal structure control. [ 8,9 ] Previously, we found ACd 4 In 5 Se 12 (A = Rb, Cs) with strong SHG in IR region (40 and 35 times that of benchmark AgGaS 2 with comparable transparency region 0.89-25 µm). [ 9 ] These sphalerite type compounds also show several signifi cances in that: 1) metals with different valence states, i.e., divalent M 2+ and trivalent M 3+ , can jointly share the center-site of each MSe 4 tetrahedron, [ 9 ] such as Cd 2+ /Ga 3+ , Cd 2+ /In 3+ , Mn 2+ /In 3+ ; that 2) the occupancy of the divalent metal can vary considerably, such as: Cd 2+ : 28%-58%, Mn 2+ , 31%-56%; and that 3) the cooperation of the divalent metal not only enhances the IR NLO property, but also introduces the coexistence of the other property, such as thermochromic property by Cd 2+ ; and magnetic property by Mn 2+ . We have concluded these as the "functionalization based on the substitutional fl exibility". [ 9,10 ] Our previous work also reveal that instead of transition metal tetrahedron, main group metal tetrahedron, as the primary building unit, can construct a supertetrahedral framework Ba 3 CsGa 5 Se 10 Cl 2 showing very strong SHG that is about 100 times that of the benchmark AgGaS 2 in the particle size of 30-46 µm. [ 11 ] The 3D covalent framework is built by supertetrahedral Ga 4 Se 10 clusters (T2, a group of four apex-shared GaSe 4 tetrahedra) and single GaSe 4 tetrahedron (T1, as node). Interestingly, such a supertetrahedral framework exhibits not only very strong IR SHG, but also photoluminescence. Yet, the poor crystallinity and the low laser damage threshold prevent its application as a useful NLO material. We are therefore eager to further improve the performance and functionalize such a supertetrahedral framework via introducing transition metal (M) ions. However, the simple "Ga-to-M substitution" will be

To reduce cost and improve environmental sustainability, there continues to be an important need for the development of efficient organic light‐emitting diodes (OLEDs) that do not rely on heavy metal‐containing compounds. In particular, the efficiency of fluorescent near‐infrared (NIR) OLEDs continues to lag well‐behind that of their platinum‐containing counterparts. Low efficiencies in this spectral range mainly arise from the low quantum yields of fluorescent NIR emitters due to the energy gap law and inefficient harvesting of triplet excitons. In this paper, a thermally activated delayed fluorescent (TADF) material is used as the assistant dopant to demonstrate pure NIR‐emitting fluorescent OLEDs with an external quantum efficiency of up to 3.8%, with an electroluminescence maximum at 840 nm and a spectral full‐width at half‐maximum of < 40 nm. The efficiency is more than three times higher than that of the best previously reported fluorescent OLEDs in this spectral range and approaches that achievable with the best platinum‐containing phosphorescent emitters.

Search for two-dimensional (2D) water-splitting photocatalysts is crucial to solve energy crises and environmental problems.  In this research, we study the electronic and photocatalytic properties of single-layer Ga2X1X2 (Ga2SeTe, Ga2STe, and Ga2SSe) and newly proposed α-Ga2S3/Ga2SSe-A, α-Ga2S3/Ga2SSe-B, and α-Ga2S3/Ga2SSe-C van der Waals heterojunctions using first-principles calculations. Theoretical results indicate that Ga2X1X2 monolayers present suitable band edges. 2D α-Ga2S3/Ga2SSe-B and α-Ga2S3/Ga2SSe-C belong to type-II heterojunctions and under biaxial strains embody suitable band edges. Comparisons of the valence band maximum charge and electric dipole of α-Ga2S3/Ga2SSe-A and α-Ga2S3/Ga2SSe-B demonstrate that it is possible to achieve suitable band edges for water splitting by switching electric dipoles. Especially, the three Ga2X1X2 monolayers and α-Ga2S3/Ga2SSe-B and α-Ga2S3/Ga2SSe-C heterojunctions absorb a large amount of visible light, thus proving that they are promising photocatalysts for water splitting. More importantly, we find that the optical absorption coefficients of 2D monolayers and heterojunctions in previous calculations are several times underestimated because the effective volume is not taken into consideration. To obtain reliable absorption coefficients, the real and imaginary parts of dielectric function must be renormalized.

Recently researchers have found that the non-resonant second-harmonic generation (SHG) intensity of the GaSe monolayer (ML) is the strongest among all two-dimensional (2D) atomic layered crystals. Here we perform a systematic first-principles study of the SHG coefficient of GaX (X = S, Se, Te) monolayers (MLs) and few-layers. We find that the non-resonant SHG intensity of the GaS ML can be comparable with that of the GaSe ML, while the non-resonant SHG intensity of the GaTe ML is much stronger than that of the GaSe ML. Furthermore, the magnitudes of SHG coefficients of the few-layers exfoliated from bulk ε-GaSe and newly constructed N-GaSe crystals are very close to that of the GaSe ML, showing no dependence on the layer number. The magnitude of the SHG coefficient of the trilayer exfoliated from the bulk β-GaSe crystals is around 1/3 of that of the GaSe ML, decreasing rapidly with the layer number. This study indicates that a strong SHG response can be obtained in a wide range of monolayers and few-layers. Moreover, we point out that one can identify the layer number and the stacking sequence of 2D nanosheets by measuring their elastic constants and SHG coefficients.