Clar's Aromatic π-Sextet Rule for the Construction of Red Multiple Resonance Emitter.

Despite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π-sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π-sextets). Theoretical studies indicate that the quantity of π-sextets ultimately determines the optical bandgap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94% and horizontal dipole ratio of ~90%, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light-emitting diode shows a high external quantum efficiency of 27.3%, with only a slight decrease of 3.7% at an elevated luminance level of 100,000 cd/m2.

Cascade Effect of a Dimerized Thermally Activated Delayed Fluorescence Dendrimer.

Thermally activated delayed fluorescence (TADF) emitters with a high horizontal orientation are highly essential for improving the external quantum efficiency (EQE) of organic light-emitting diodes; however, pivotal molecular design strategies to improve the horizontal orientation of solution processable TADF emitters are still scarce and challenging. Herein, a phenyl bridge is adopted to connect the double TADF units, and a dimerized TADF dendrimer, D4CzBNPh-SF, is successfully constructed. Compared to counterpart with single TADF unit, the proof-of-the-concept molecule not only exhibits an improved horizontal dipole ratio (78%) due to the π-delocalization-induced extended molecular conjugation, but also displays a faster reversed intersystem crossing rate constant (6.08×106 s-1) and a high photoluminescence quantum yield of 95% in neat film. Consequently, the non-doped solution-processed device with D4CzBNPh-SF as the emitter, achieves an ultra-high maximum EQE of 32.6%, which remains at 26.6% under a luminance of 1000 cd/m2. Furthermore, using D4CzBNPh-SF as a sensitizer, the TADF-sensitized fluorescence device exhibits a high maximum EQE of 30.7% at a luminance of 575 cd/m2 and a full width at half maximum of 36 nm.

Single Wavelength Laser Excitation Ratiometric NIR-II Fluorescent Probe for Molecule Imaging in Vivo.

Fluorescence (FL) imaging in the second near-infrared window (NIR-II, 1000-1700 nm) has emerged as a promising bioimaging modality that enables noninvasive visualization of deep tissue with an unprecedented resolution. However, there is a paucity of studies on high-quality responsive NIR-II FL molecules. Herein we report a novel activated NIR-II FL molecule, 4,7-bis(5-(4-(diphenylamine)phenyl)-2-thiophene) [1,2,5]selenadiazolo[3,4-f]benzo[c][1,2,5]thiadiazole (SeTT), which exhibits fast and specific responsive capability to hypochlorous acid (HClO). To obtain the NIR-II ratiometric nanoprobe, SeTT was encapsulated on the surface of Er3+-doped down-conversion nanoparticles (DCNP), achieving the DCNP@SeTT nanoprobe. With a single 980 nm laser excitation, the ratiometric FL signal of SeTT at 1150 nm and DCNP at 1550 nm (I1150 nm/I1550 nm) was linearly correlated with the concentration of HClO with a detection limit of 0.4 µM. The ratiometric nanoprobe was successfully investigated for variations in HClO concentration in the tumor progression, visualization of anatomical structures of the peritoneal cavity in the mice model with inflammation, and quantitative detection of the HClO concentration in a rabbit model of osteoarthritis, achieving a fast response and high selectivity for the detection of HClO. The NIR-II-responsive nanoprobe can serve as a promising and effective tool for highly sensitive monitoring and imaging of HClO in living systems.

Dye-Modified Metal-Organic Framework as a Recyclable Luminescent Sensor for Nicotine Determination in Urine Solution and Living Cell.

A water-stable and pH-independent sensor for qualitative and quantitative detection of nicotine in urine solution and living cell was successfully developed. This material, named MB@UiO-66-NH2, can be synthesized by encapsulating methylene blue (MB) with a well-known metal-organic framework (MOF) UiO-66-NH2 through a simple impregnation method. The fluorescence intensity of the system was significantly enhanced when a certain amount of nicotine was added. In the meanwhile, MB is reduced by reductive nicotine to form leucomethylene blue (LB). The proposed sensor displayed excellent selectivity and sensitivity toward nicotine with limit of detection (LOD) of 0.98 µM, which is comparable or even better than that of the electrochemistry detecting methods for nicotine. The obvious enhancement and blue shift of the emission arise from the photoinduced electron transfer (PET) from LB to the UiO-66-NH2. The photophysical properties and the sensing applications of MB@UiO-66-NH2 suggest that this composite can be acted as a sensitive, selective, recyclable, and fluorogenic sensor for nicotine determination in urine solution and living cell.