Design of mechanical-robust phosphorescence materials through covalent click reaction

Highly flame retardancy, barrier, mechanical and persistent antibacterial polylactic acid film with high-parallel interconnected thousand layered cake architecture

In this work, a bio-based material (CGP) is obtained by combing chitosan, gelatin and polyvinyl alcohol through a simple solution mixing to simultaneously address polylactic acid film (PLA)' flammability and poor barrier, toughness and antibacterial properties by soaking. The results of open fire testing show that modified PLA films can effectively prolong the combustion time, improve the thermal stability and reduce the release of heat in the cone calorimeter test. For the PLA sample after soaking for 5 times (PLA-5) in particular, it can reduce the peak heat release rate (pHRR) and total heat release (THR) values to 85.8 kW/m2 and 1.3 MJ/m2 from the values of 129.5 kW/m2 and 1.8 MJ/m2 for PLA, respectively. Structural analysis suggests that CGP primarily operates in the condensed phase by forming physical barriers. Meanwhile, the modified PLA films can exhibit superior barrier effects, which indicate the oxygen transmission rate value of PLA-5 decreases to 0.9 cm3/(m2·day) from the 392.5 cm3/(m2·day) of raw PLA film. Moreover, the PLA-5 also have excellent toughness (the value increased to 200.5 % from 31.0 %) and persistent antibacterial effects (it still has 100 % sterilization after 500 days).

Achieving Bright and Long-Lived Aqueous Room-Temperature Phosphorescence of Carbon Nitrogen Dots Through In Situ Host-Guest Binding

The development of bright and long-lived aqueous room-temperature phosphorescent (RTP) materials holds paramount importance in broadening the application scope of RTP material system. However, the conventional RTP materials usually exhibit low efficiency and short lifetime in aqueous solution. Herein, an in situ host-guest strategy is proposed to achieve cyanuric acid (CA)-derived phosphorescent carbon nitrogen dots (CNDs) composite (CNDs@CA) that demonstrates a significant enhancement of both quantum yield (QY) and lifetime mediated by water. Detailed investigations reveal that the robust hydrogen bonding networks between CNDs@CA and water effectively stabilize triplet excitons and suppress nonradiative decays, as well as facilitate efficient energy transfer from CA to CNDs, thereby prolonging the lifetime and enhancing the efficiency of RTP. The phosphorescent QY and lifetime of CNDs@CA can be increased to 26.89% (3.9-fold increase) and 951.25 ms (5.5-fold increase), respectively, with the incorporation of 50 wt% water under ambient conditions. Even in fully aqueous environments (with up to 400 wt% water added), CNDs@CA exhibits persistent water-boosted RTP properties, demonstrating exceptional stability. The robust water-boosted RTP property of CNDs@CA in aqueous solutions presents significant potential for high signal-to-noise ratio afterglow bioimaging as well as advanced information encryption.

Computational and Experimental Investigations of Osmium-Rich Borides Hf2MOs5B2 (M = Mn, Fe, Co): From Spin Glass to Room-Temperature Magnetic Behaviors

The metal borides, Hf2MOs5B2 (M = Mn, Fe, Co), which are the first Os-rich quaternary variants of the prolific Ti3Co5B2 structure type, were investigated computationally and experimentally. In their crystal structures, osmium builds a network of prisms, in which the other elements are located. The magnetic M elements are found in face-connected Os8 square prisms leading to M-chains with intra- and interchain distances of about 3.0 and 6.5 Å, respectively. Density functional theory (DFT) showed that magnetic ordering is hugely favored for M = Mn and Fe but only slightly favored for M = Co. Experimental investigations then confirmed and extended the DFT predictions as a metamagnetic behavior was found for the M = Mn and Fe phases, whereby the antiferromagnetic interactions (TN = 19 and 90 K) found at low magnetic fields change to ferromagnetic at higher fields. A very broad transition (TN = 45 K) is found for M = Co, suggesting spin-glass behavior for this phase. For M = Fe, a hard-magnet hysteresis at 5 K is found with a 40 kA/m coercivity, and even at room temperature, a significant hysteresis is found. This study paves the way for the discovery of Os-based magnets in this structure type and other intermetallics.

Visible-light-excited robust room-temperature phosphorescence of dimeric single-component luminophores in the amorphous state

Organic room temperature phosphorescence (RTP) has significant potential in various applications of information storage, anti-counterfeiting, and bio-imaging. However, achieving robust organic RTP emission of the single-component system is challenging to overcome the restriction of the crystalline state or other rigid environments with cautious treatment. Herein, we report a single-component system with robust persistent RTP emission in various aggregated forms, such as crystal, fine powder, and even amorphous states. Our experimental data reveal that the vigorous RTP emissions rely on their tight dimers based on strong and large-overlap π-π interactions between polycyclic aromatic hydrocarbon (PAH) groups. The dimer structure can offer not only excitons in low energy levels for visible-light excited red long-lived RTP but also suppression of the nonradiative decays even in an amorphous state for good resistance of RTP to heat (up to 70 °C) or water. Furthermore, we demonstrate the water-dispersible nanoparticle with persistent RTP over 600 nm and a lifetime of 0.22 s for visible-light excited cellular and in-vivo imaging, prepared through the common microemulsion approach without overcaution for nanocrystal formation.

Management of triplet excitons transition: fine regulation of Förster and dexter energy transfer simultaneously

Understanding and management of triplet excitons transition in the same molecule remain a great challenge. Hence, for the first time, by host engineering, manageable transitions of triplet excitons in a naphthalimide derivative NDOH were achieved, and monitored through the intensity ratio (ITADF/IRTP) between thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP). Energy differences between lowest triplet excited states of host and guest were changed from 0.03 to 0.17 eV, and ITADF/IRTP of NDOH decreased by 200 times, thus red shifting the afterglow color. It was proposed that shorter conjugation length led to larger band gaps of host materials, thus contributing to efficient Dexter and inefficient Förster energy transfer. Interestingly, no transition to singlet state and only strongest RTP with quantum yield of 13.9% could be observed, when PBNC with loosest stacking and largest band gap acted as host. This work provides novel insight for the management and prediction of triplet exciton transitions and the development of smart afterglow materials.

Chaperone Mimetic Strategy for Achieving Organic Room-Temperature Phosphorescence based on Confined Supramolecular Assembly

The development of organic materials that deliver room-temperature phosphorescence (RTP) is highly interesting for potential applications such as anticounterfeiting, optoelectronic devices, and bioimaging. Herein, a molecular chaperone strategy for controlling isolated chromophores to achieve high-performance RTP is demonstrated. Systematic experiments coupled with theoretical evidence reveal that the host plays a similar role as a molecular chaperone that anchors the chromophores for limited nonradiative decay and directs the proper conformation of guests for enhanced intersystem crossing through noncovalent interactions. For deduction of structure-property relationships, various structure-related descriptors that correlate with the RTP performance are identified, thus offering the possibility to quantitatively design and predict the phosphorescent behaviors of these systems. Furthermore, application in thermal printing is well realized for these RTP materials. The present work discloses an effective strategy for efficient construction of organic RTP materials, delivering a modular model which is expected to help expand the diversity of desirable RTP systems.

Facile Preparation of Full-Color Tunable Room Temperature Phosphorescence Cellulose via Click Chemistry

Sustainable long-lived room temperature phosphorescence (RTP) materials with color-tunable afterglows are attractive but rarely reported. Here, cellulose is reconstructed by directed redox to afford ample active hydroxyl groups and water-solubility; arylboronic acids with various π conjugations can be facilely anchored to reconstructed cellulose via click chemistry within 1 min in pure water, resulting in full-color tunable RTP cellulose. The rigid environment provided by the B─O covalent bonds and hydrogen bonds can stabilize the triplet excitons, thus the target cellulose displays outstanding RTP performances with the lifetime of 2.67 s, phosphorescence quantum yield of 9.37%, and absolute afterglow luminance of 348 mcd m-2 . Furthermore, due to the formation of various emissive species, the smart RTP cellulose shows excitation- and time-dependent afterglows. Taking advantages of sustainability, ultralong lifetime, and full-color tunable afterglows, et al, the environmentally friendly RTP cellulose is successfully used for nontoxic afterglow inks, delay lighting, and afterglow display.