The synthesis as well as the structural and photophysical characterization of two isoleptic bis-cyclometalated Pt(II) and Pd(II) complexes, namely [PtL] and [PdL], bearing a tailored dianionic tetradentate ligand (L2-) are reported. The isostructural character and intermolecular interactions of [PtL] and [PdL] were assessed by NMR spectroscopy and X-ray diffraction analysis. Both complexes show fully ligand-controlled aggregation, demonstrating that a judicious molecular design can tune the photophysical properties. In fact, by introduction of fluorine atoms on defined positions and methoxy groups on complementary sites, metal-metal interactions can be forced by a head-to-tail stacking. Hence, [PtL] shows luminescence from metal-perturbed ligand-centered or from metal-metal-to-ligand charge-transfer triplet states in diluted solutions, in frozen glasses and in crystals, with high photoluminescence quantum yields and long lifetimes in the microsecond range. At room temperature (RT) in concentrated fluid solutions, the palladium analogue [PdL] surprisingly emits luminescence from aggregated species involving supramolecular interactions. Time-resolved photoluminescence and transient absorption spectroscopies demonstrated that ultrafast intersystem crossing occurs for both metals, which outruns any competitive relaxation pathway from the photoexcited singlet state. Furthermore, we demonstrate that the radiationless deactivation can be suppressed in frozen glassy matrices at 77 K and by intermolecular interactions in fluid solutions at RT. In both cases and as indicated by density functional theory calculations, the lowest emissive state acts as an energy trap from which the thermal population of dissociative states with formal occupation of an antibonding Pd-centered 4dx2-y2 orbital is suppressed. This occurs as the energy gap between the emissive and the dark states surpasses kT.

Room-Temperature Phosphorescence from Pd(II) and Pt(II) Complexes as Supramolecular Luminophores: The Role of Self-Assembly, Metal-Metal Interactions, Spin-Orbit Coupling, and Ligand-Field Splitting.

A new ABW-type luminescent metal–organic framework (MOF) namely (H3O)[Zn2L(H2O)]·3NMP·6H2O (1), constructed with eco-friendly Zn2+ and the multicarboxylate intraligand (LH5) was designed, synthesized and fully characterized by X-ray single-crystal diffraction, steady-state absorption and emission spectroscopy, and SEM observations. The MOF-based suspension sensor 1 (NMP) demonstrated high sensitivity to low-concentration pesticides of chlorothalonil (CTL), nitrofen (NF), trifluralin (TFL), and 2,6-dichloro-4-nitroaniline (DCN), which was assigned to the synergistic effect of the photoinduced electron transfer and the fluorescence resonance energy transfer. With the highest luminescent detection efficiency (KSV up to 11.194 μmol−1 and LOD down to 2.93 ppm) to DCN, 1 (NMP) was successfully applied for the selective sensing of DCN. The MOF-based film sensor 1 (film) illustrated the selective visualization sensing of trace amounts of DCN. In addition, based on the high saturated vapor pressure of TFL and the unique bathochromic shift effect to the emission maxima of 1, the MOF-based luminescent vapor sensing device 1 (LED) successfully exhibited operability for sensing of TFL vapor. The results illustrated a feasible approach to construct new MOF-based luminescent sensors for selective sensing and visualization of pesticides.

/pdf/selective-sensing-and-visualization-of-pesticides-by-abw-4l6yh494j7.pdf

Selective sensing and visualization of pesticides by ABW-type metal─organic framework based luminescent sensors

Preparation of AIEgens with excellent photostability is of vital importance to acquire the optimal performance of aggregation-induced emission (AIE) and remains challenging. In this paper, a handy structural design strategy based on iridium(III) complexes for the creation of photostable AIEgens is reported. The synergistic effect of phenyl and carbazole improves the rotational activity of substituents, then activates the AIE property of iridium(III) complexes with considerably improved photostability. In addition, prompt and high-resolution imaging of latent fingerprints on tinfoil, glass, plastic, and steel is presented by immersion in an aqueous solution of IrCzPh for 60 s. With the aid of photostable AIE, legible and intact fingerprint images demonstrate ultrahigh definition, which can display down to level 3 of fingerprint details and accurately authenticate individual characteristics. Meanwhile, outstanding anti-aging performance of fingerprint images is emerged with no contrast attenuation under 365 nm irradiation for 60 min or aged in natural light for 7 days. Noteworthily, ultrahigh-contrast dynamic imaging of local fingerprint details is achieved. 

Photostable aggregation-induced emission of iridium(III) complex realizing robust and high-resolution imaging of latent fingerprints

Three Ir(III) complexes IrC1, IrC2, and IrC3 substituted with 4-(diphenylamino)phenyl (TPA), 4-(9H-carbazol-9-yl)phenyl (Cz1), and 9-phenyl-9H-carbazol-3-yl (Cz2) moieties were prepared and fully characterized as phosphorescent emitters. In comparison with Ir(ppy)3, introduction of TPA, Cz1, and Cz2 moieties strongly improved the oxygen sensitivities of IrC1–IrC3. Short-decayed IrC1 with I0/I100 of 168.6 and KappSV of 202.2 bar−1 in THF exhibited the highest sensitivity for oxygen. TPA and Cz moieties caused remarkable collision radius variations of the Ir(III) complexes with 2.13 ± 0.08 for σIrC1/σIr(ppy)3, 1.24 ± 0.06 for σIrC2/σIr(ppy)3, and 1.54 ± 0.08 for σIrC3/σIr(ppy)3. For demonstrating the dependence of oxygen sensitivity on the molecular structure of the oxygen-sensitive probes (OSPs), the delocalization of spin populations (DSPs) has been applied for the first time to confirm the collision radius variations of Ir(III) complexes. Remarkable DSPs were found on the TPA, Cz1, and Cz2 moieties with the spin population (percentage of the spin population) of 0.23210 (11.61%), 0.08862 (4.43%), and 0.13201 (6.60%), respectively. And strong linear correlations (R2 = 0.997) between the collision radius variations and spin population on TPA and Cz moieties were apparent. The DSPs could be used to describe the dependence of oxygen sensitivity on the molecular structure of the OSPs. For achieving real-time oxygen sensing, the photostability, oxygen sensing performance, and operational stability of IrC1–IrC3 and Ir(ppy)3 immobilized in ethyl cellulose (EC) were investigated. The IrC1-EC film demonstrated outstanding photostability after 60 min of irradiation and excellent operational stability for continuous oxygen monitoring with no attenuation of the original emission intensity in 4000 s. This study quantified and analyzed the dependence of oxygen sensitivity on the molecular structure of Ir(III) complexes for the first time and illustrated a feasible approach to achieve high-efficiency sensors for real-time monitoring of oxygen.

/pdf/the-dependence-of-oxygen-sensitivity-on-the-molecular-g1b521mtaw.pdf

The dependence of oxygen sensitivity on the molecular structures of Ir(iii) complexes and their application for photostable and reversible luminescent oxygen sensing

Study of optical properties of 2,7-dioctyl[1]benzothieno[2,3-b]benzothiophene (C8BTBT) is promising for applications in low-cost and flexible optoelectronic devices. Here, we systematically investigated the thickness dependent structural and photophysical properties of large-area C8BTBT films. The large-area C8BTBT thin films of different thicknesses below 80 nm were prepared by off-centre spin coating method. Grazing incidence X-ray diffraction measurements confirm the highly crystalline nature of the thin films and reveal that crystal coherence length increases with increase of film thickness. The film morphology and its thickness were studied using atomic force microscopy. Further, optical absorption and emission behaviors of the thin films were analyzed. The results show strong ultraviolet (UV) emissions at room temperature. The pphotoluminescence behaviour of higher-thickness films differs from that of lower-thickness films. The thickness dependent UV emission spectra are explained in terms of defects and aggregation behavior of C8BTBT thin films. We determine the impact of thickness and aggregation (J- and H-type) on emission behaviors of the C8BTBT thin films. Our findings open a new avenue for the future optimization and prospective applications in photonics based on two-dimensional organic semiconductors. 

Aggregation Induced Strong Photoluminescence at Room Temperature in Large-Area C8BTBT Thin Films

Three triphenylamine (TPA) substituted cyclometalated Ir(III) complexes IrA1, IrA2, and IrA3 based on Ir(ppy)3 were synthesized and applied as phosphorescent probes for the monitoring of molecular oxygen. The phosphorescence intensity of all the Ir(III) complexes in tetrahydrofuran (THF) was gradually quenched with an increase of oxygen concentration. The increase of TPA substituents on the meta-position of 2-phenylpyridine (IrA1-IrA3) gradually improved the oxygen sensitivity of cyclometalated Ir(III) complexes. IrA3 showed the highest oxygen sensitivity in THF with a KappSV of 204.8 bar−1 and a limit of detection (LOD) of 0.27 mbar. The relationship between molecular structure and the collision radiuses (σ) of all the Ir(III) complexes has been investigated on the basis of the Demas model and the fundamental expression of luminescence quenching systems by oxygen. The ratio of collision radiuses are σIrA1/σIr(ppy)3 = 1.27 ± 0.05, σIrA2/σIr(ppy)3 = 1.72 ± 0.10, and σIrA3/σIr(ppy)3 = 2.13 ± 0.07, respectively. The introduction and increase of TPA substituents can obviously increase the collision radiuses of cyclometalated Ir(III) complexes which leading to potential oxygen sensitivity. And the incremental effect of collision radiuses caused by the introduction of TPA substituents resulted in outstanding oxygen sensitivity of IrA3. The results demonstrate for the first time evidence between molecular structure and oxygen sensitivity of the emitters for optical sensing.

https://pubs.rsc.org/en/content/articlepdf/2018/RA/C8RA07115B

The influence of molecular structure on collision radius for optical sensing of molecular oxygen based on cyclometalated Ir(III) complexes

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The influence of molecular structure on collision radius for optical sensing of molecular oxygen based on cyclometalated Ir(III) complexes