Organic long‐persistent luminescence (OLPL) materials have attracted wide attention on account of their fascinating luminescence properties, presenting application prospects in the fields of bioimaging, information security, displays, anti‐counterfeiting, and so on. Some effective strategies have been developed to promote the intersystem crossing (ISC) of the excited singlet state to triplet state and limit nonradiative transition, and thus OLPL materials with long lifetime (more than 1s) and high quantum yield have been explored. However, OLPL materials with dynamic and excitation‐dependent characteristics are rarely reported. In this work, two novel polyphosphazene derivatives containing carbazolyl units are designed and synthesized successfully, and then they are doped into poly(vinyl alcohol) (PVA) films to achieve polymeric long‐persistent luminescence (PLPL). Unexpectedly, excitation‐dependent PLPL (ED‐PLPL) is obtained under ambient conditions (in air at room temperature), and the persistent luminescence color can be changed from blue to green upon varying the excitation wavelength. At the same time, a dynamic cycle of ED‐PLPL is realized based on the formation and destruction of hydrogen bonding interactions between the PVA chains and polyphosphazene phosphor. This work provides a new strategy for the design of color‐tunable polymeric luminescent materials under ambient conditions.

Room temperature phosphorescence (RTP) has drawn extensive attention in recent years. Efficient stimulus-responsive phosphorescent organic materials are attractive, but are extremely rare because of unclear design principles and intrinsically spin-forbidden intersystem crossing. Herein, we present a feasible and facile strategy to achieve ultraviolet irradiation-responsive ultralong RTP (IRRTP) of some simple organic phosphors by doping into amorphous poly(vinyl alcohol) matrix. In addition to the observed green and yellow afterglow emission with distinct irradiation-enhanced phosphorescence, the phosphorescence lifetime can be tuned by varying the irradiation period of 254 nm light. Significantly, the dynamic phosphorescence lifetime could be increased 14.3 folds from 58.03 ms to 828.81 ms in one of the obtained hybrid films after irradiation for 45 min under ambient conditions. As such, the application in polychromatic screen printing and multilevel information encryption is demonstrated. The extraordinary IRRTP in the amorphous state endows these systems with a highly promising potential for smart flexible luminescent materials and sensors with dynamically controlled phosphorescence.

Flexible hydrogen-bonded organic frameworks (FHOFs) are quite rare but promising for applications in separation, sensing and host-guest chemistry. They are difficult to stabilize, making their constructions a major challenge. Here, a flexible HOF (named 8PN) with permanent porosity has been successfully constructed. Nine single crystals of 8PN with different pore structures are obtained, achieving a large-scale void regulation from 4.4% to 33.2% of total cell volume. In response to external stimuli, multimode reversible structural transformations of 8PN accompanied by changes in luminescence properties have been realized. Furthermore, a series of high-quality co-crystals containing guests of varying shapes, sizes, aggregation states and even amounts are obtained, showing that 8PN can adapt to different guests by regulating the molecular conformations and assembling forms of its building blocks. The unexpected flexibility of 8PN makes it a promising material for enriching the applications of existing porous materials.

A bulk dielectric polymer film with an intrinsic ultralow k value of 1.52 at 10 kHz has been successfully synthesized based on a novel polyimide FPTTPI. More importantly, such outstanding dielectric properties remain stable up to 280°C. The excellent ultralow dielectric properties are mainly because of the larger free volume (subnanoscale), which intrinsically exists in the amorphous region of polymeric materials. Meanwhile, FPTTPI also shows excellent thermal stability and mechanical properties, with a glass-transition temperature (T g ) of 280°C, 5 wt % loss temperature of 530°C, and a residual of 63% at 800°C under N 2 . It was soluble in common solvents, which made it possible to undergo simple spin-on or efficient, low-cost, and continuous roll-to-roll processes. ■ INTRODUCTIONWith the development of ultralarge-scale integration (ULSI) to high speed and high integration in the semiconductor industry, and with the continuing miniaturization in the dimensions of electronic devices utilized in ULSI circuits, an urgent need exists for high-performance low-k and ultralow-k dielectric materials (low-k: k ≤ 2.5; ultralow-k: k ≤ 2.0) has arisen. 1−4 Such dielectrics materials would reduce the capacitance between the metal interconnects, the resistance-capacitance delay, the line-to-line crosstalk noise, and the power dissipation; 5−7 these materials also have important application prospects in the fields of interlayer dielectric, semiconductor packaging (chips modules, etc.), and high-frequency, low-loss boards etc. So far, research of low-dielectric materials as an alternative to the workhorse dielectrics silicon dioxide (k = 3.9−4.3) are continually being pursued today, which mainly including organosilicates and organic polymers. 8−13 Compared with inorganic dielectric materials, organic polymer materials often have a lower dielectric constant, because of the lower materials density and lower individual bond polarizability. Moreover, they show distinct advantages, in terms of easy chemical and geometric structural design. 14−18 Thus, they have attracted much interest. Generally, by decreasing the dipole strength or the number of dipoles or a combination of both, the dielectric constant of full dense polymer materials can be lowered to 2.2−2.6. 5,19−22 The most common way is fluorination of dielectric materials or increasing the free volume by rearranging the material structure. 23−27 However, it seems that no true dielectric generational extendibility to the ultralow-k region can be achieved without embracing the concept of porosity, either for organosilicates or organic polymers. 28−32 The k-value of these porous materials can be less than 1.5, 33−39 but the method itself is complicated, difficult to control, and expensive. Moreover, the pore structure, the size, and the distribution would greatly affect the homogeneity of the materials, which makes this technique difficult for large-area applications. In addition, the porosity tends to dramatically reduce the mechanical strength and increase the permeability o...

Long-lived organic room-temperature phosphorescence (RTP) has sparked intense explorations, owing to the outstanding optical performance and exceptional applications. Because triplet excitons in organic RTP experience multifarious relaxation processes resulting from their high sensitivity, spin multiplicity, inevitable nonradiative decay, and external quenchers, boosting RTP performance by the modulated triplet-exciton behavior is challenging. Herein, we report that cross-linked polyphosphazene nanospheres can effectively promote long-lived organic RTP. Through molecular engineering, multiple carbonyl groups (CO), heteroatoms (N and P), and heavy atoms (Cl) are introduced into the polyphosphazene nanospheres, largely strengthening the spin−orbit coupling constant by recalibrating the electronic configurations between singlet (S n ) and triplet (T n ) excitons. In order to further suppress nonradiative decay and avoid quenching under ambient conditions, polyphosphazene nanospheres are encapsulated with poly(vinyl alcohol) matrix, thus synchronously prompting phosphorescence lifetime (173 ms longer), phosphorescence efficiency (∼12-fold higher), afterglow duration time (more than 20 s), and afterglow absolute luminance (∼19-fold higher) as compared with the 2,3,6,7,10,11hexahydroxytriphenylene precursor. By measuring the emission intensity of the phosphorescence, an effective probe based on the nanospheres is developed for visible, quantitative, and expeditious detection of volatile organic compounds. More significantly, the obtained films show high selectivity and robustness for anisole detection (7.1 × 10 −4 mol L −1 ). This work not only demonstrates a way toward boosting the efficiency of RTP materials but also provides a new avenue to apply RTP materials in feasible detection applications.