Flexible molecular crystals for optoelectronic applications.

The cornerstones of the advancement of flexible optoelectronics are the design, preparation, and utilization of novel materials with favorable mechanical and advanced optoelectronic properties. Molecular crystalline materials have emerged as a class of underexplored yet promising materials due to the reduced grain boundaries and defects anticipated to provide enhanced photoelectric characteristics. An inherent drawback that has precluded wider implementation of molecular crystals thus far, however, has been their brittleness, which renders them incapable of ensuring mechanical compliance required for even simple elastic or plastic deformation of the device. It is perplexing that despite a plethora of reports that have in the meantime become available underpinning the flexibility of molecular crystals, the "discovery" of elastically or plastically deformable crystals remains limited to cases of serendipitous and laborious trial-and-error approaches, a situation that calls for a systematic and thorough assessment of these properties and their correlation with the structure. This review provides a comprehensive and concise overview of the current understanding of the origins of crystal flexibility, the working mechanisms of deformations such as plastic and elastic bending behaviors, and insights into the examples of flexible molecular crystals, specifically concerning photoelectronic changes that occur in deformed crystals. We hope this summary will provide a reference for future experimental and computational efforts with flexible molecular crystals aimed towards improving their mechanical behavior and optoelectronic properties, ultimately intending to advance the flexible optoelectronic technology.

Coplanar Conformational Structure of π-Conjugated Polymers for Optoelectronic Applications.

Hierarchical structure of conjugated polymers is critical to dominating their optoelectronic properties and applications. Compared to nonplanar conformational segments, coplanar conformational segments of conjugated polymers (CPs) demonstrate favorable properties for applications as a semiconductor. Herein, recent developments in the coplanar conformational structure of CPs for optoelectronic devices are summarized. First, this review comprehensively summarizes the unique properties of planar conformational structures. Second, the characteristics of the coplanar conformation in terms of optoelectrical properties and other polymer physics characteristics are emphasized. Five primary characterization methods for investigating the complanate backbone structures are illustrated, providing a systematical toolbox for studying this specific conformation. Third, internal and external conditions for inducing the coplanar conformational structure are presented, offering guidelines for designing this conformation. Fourth, the optoelectronic applications of this segment, such as light-emitting diodes, solar cells, and field-effect transistors, are briefly summarized. Finally, a conclusion and outlook for the coplanar conformational segment regarding molecular design and applications are provided.

The closed-loop control method based on dual-port adaptive internal model control for fine image stabilization of space telescopes.

In view of the complex working environment of space astronomical telescopes, the influence of various disturbance sources on the imaging quality cannot be ignored. This paper focuses on compensating for the space telescope line-of-sight (LOS) deviation and suppressing the low-frequency disturbance problem in astronomical observation. A closed-loop control method based on dual-port adaptive internal model control (AIMC) for the fine image stabilization system (FISS) was proposed. To be specific, the fine guidance sensor (FGS) as the high-precision detection unit of the FISS calculates the telescope LOS deviation and sends it to the controller unit in real time. The controller unit drives the large-aperture fast steering mirror (FSM), which performs high-precision two-dimensional rotation to compensate for the telescope LOS deviation, according to the dual-port AIMC control algorithm. Moreover, the dual-port AIMC control method adds an AIMC loop on the basis of the feedback loop and adjusts the filter parameters adaptively according to the target angular velocity of the FSM, achieving higher disturbance suppression capability. The experimental results verify that the control method proposed can effectively compensate for the LOS deviation and suppress the composite frequency disturbance. In the 0-8 Hz frequency band, the power spectral density integral values of the star centroid deviation in the X and Y directions of the FGS are, respectively, suppressed by 97.38% and 98.38%.

Intrinsically Stretchable and Efficient Fully Π-Conjugated Polymer via Internal Plasticization for Flexible Deep-Blue Polymer Light-Emitting Diodes with CIEy = 0.08.

Intrinsically stretchable polymeric semiconductors are essential to flexible polymer light-emitting diodes (PLEDs) owing to their excellent strain tolerance capacity under long-time deformation operation. Obtaining intrinsic stretchability, robust emission properties, and excellent charge-transport behavior simultaneously from fully π-conjugated polymers (FCPs) is difficult, particularly for applications in deep-blue PLEDs. Herein, an internal plasticization strategy is proposed to introduce a phenyl-ester plasticizer into polyfluorenes (PF-MC4, PF-MC6, and PF-MC8) for narrowband deep-blue flexible PLEDs. Compared with controlled poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPFs) (2.5%), the freestanding PF-MC8 thin film shows a fracture strain of >25%. The three stretchable films exhibit stable and efficient deep-blue emission (PLQY > 50%) because of the encapsulation of π-conjugated backbone via pendant phenyl-ester plasticizers. The PF-MC8-based PLEDs show deep-blue emission, which corresponds to CIE and EQE values of (0.16, 0.10) and 1.06%, respectively. Finally, the narrowband deep-blue electroluminescence (FWHM of ≈25 nm; CIE coordinates: (0.15, 0.08)) and performance of the transferred PLEDs based on the PF-MC8 stretchable film are independent of the tensile ratio (up to 45%); however, they show a maximum brightness of 1976 cd m-2 at a ratio of 35%. Therefore, internal plasticization is a promising approach for designing intrinsically stretchable FCPs for flexible electronics.

Photoexcitation dynamics and energy engineering in supramolecular doping of organic conjugated molecules.

Doping and blending strategies are crucial means to precisely control the excited states and energy level in conjugated molecular systems. However, effective models and platforms are rarely proposed to systematically explore the effects of the formation of trapped doped centers on heterogeneous structures, energy level and ultrafast photophysical process. Herein, for deeply understanding the impact of molecular doping in film energy levels and photoexcitation dynamics, we set a supramolecular N-B coordination composed by the conjugated molecules of pyridine functionalized diarylfluorene (host material), named as ODPF-Phpy and ODPF-(Phpy)2, and the molecule of tris(perfluorophenyl)borane (BCF) (guest material). The generation of the molecular-level coordination bond increased the binding energy of N atoms and tuned the band-gap, leading to a new fluorescent emission center with longer excitation wavelength and emission wavelength. The intermolecular Förster resonance energy transfer (FRET) in blending films make it present inconsistent fluorescent behaviors compared to that in solution. The charge transfer (CT) state of N-B coordinated compounds and the changed dielectric constant of blending films resulted in a large PL spectra red-shift with the increased dopant ratio, causing a wide-tunable fluorescent color. The excited state behaviors of two compounds in blending system was further investigated by the transient absorption (TA) spectroscopy. Finally, we found supramolecular coordination blending can effectively improve the films' photoluminescence quantum yield (PLQY) and conductivity. We believe this exploration in the internal coordination mechanisms would deepen the insights about doped semiconductors and is helpful in developing novel high-efficient fluorescent systems.

Unveiling the Effects of Interchain Hydrogen Bonds on Solution Gelation and Mechanical Properties of Diarylfluorene-Based Semiconductor Polymers.

The intrinsically rigid and limited strain of most conjugated polymers has encouraged us to optimize the extensible properties of conjugated polymers. Herein, learning from the hydrogen bonds in glucose, which were facilitated to the toughness enhancement of cellulose, we introduced interchain hydrogen bonds to polydiarylfluorene by amide-containing side chains. Through tuning the copolymerization ratio, we systematically investigated their influence on the hierarchical condensed structures, rheology behavior, tensile performances, and optoelectronic properties of conjugated polymers. Compared to the reference copolymers with a low ratio of amide units, copolymers with 30% and 40% amide units present a feature of the shear-thinning process that resembled the non-Newtonian fluid, which was enabled by the interchain dynamic hydrogen bonds. Besides, we developed a practical and universal method for measuring the intrinsic mechanical properties of conjugated polymers. We demonstrated the significant impact of hydrogen bonds in solution gelation, material crystallization, and thin film stretchability. Impressively, the breaking elongation for P4 was even up to ~30%, which confirmed the partially enhanced film ductility and toughness due to the increased amide groups. Furthermore, polymer light-emitting devices (PLEDs) based on these copolymers presented comparable performances and stable electroluminescence (EL). Thin films of these copolymers also exhibited random laser emission with the threshold as low as 0.52 µJ/cm2, suggesting the wide prospective application in the field of flexible optoelectronic devices.

[Experimental Methods and Result Analysis of a Variety of Spectral Reflectance Properties of the Thin Oil Film].

In order to analysis the oil spill situation based on the obtained data in airborne aerial work, it's needed to get the spectral reflectance characteristics of the oil film of different oils and thickness as support and to select the appropriate operating band. An experiment is set up to measure the reflectance spectroscopy from ultraviolet to near-infrared for the film of five target samples, which means petrol, diesel, lubricating oil, kerosene and fossil, using spectral measurement device. The result is compared with the reflectance spectra of water in the same experimental environment, which shows that the spectral reflection characteristics of the oil film are related to the thickness and the type of the oil film. In case of the same thickness, the spectral reflectance curve of different types of film is far different, and for the same type of film, the spectral reflectance curve changes accordingly with the change of film thickness, therefore in terms of the single film, different film thickness can be distinguished by reflectance curves. It also shows that in terms of the same film thickness, the reflectance of diesel, kerosene, lubricants reaches peak around 380 nm wavelength, obviously different from the reflectance of water, and that the reflectance of crude oil is far less than that of water in more than 340 nm wavelength, and the obtained reflection spectrum can be used to distinguish between different types of oil film to some extent. The experiment covers main types of spilled oil, with data comprehensively covering commonly used detect spectral bands, and quantitative description of the spectral reflectance properties of film. It provides comprehensive theoretical and data support for the selection of airborne oil spill detection working band and the detection and analysis of water-surface oil spill.