This study presents the synthesis, crystallographic data and photophysical properties of a donor-acceptor (D-A) compound, methoxybenzylidene methanone Schiff base (HMPPM). It shows remarkable vapofluorochromism, embodied as turn-on red fluorescence in response to volatile organic compounds (VOCs), with fast response and high signal contrast. HMPPM is further developed into a cellulose sensor via dip-dying method for VOCs detection. We further use RGB and CIELAB color spaces to quantify the vapofluorochromic fluorescence. The limits of detection (LOD) of the sensor reach ppm level. Furthermore, it was fabricated into a wearable VOC sensor, with the introduction of an endogenous/exogenous reference, which conduces to high accuracy and visual identification. The cellulose sensor can be tailored into diversified patterns, with controllable shape and size, which facilitated the encapsulation into various wearables, including shoes, hat and smart band, etc., succeeding in scenario-based VOCs detection. In addition, we built a smartphone-based sensing platform based on HMPPM, which achieves a ppm-level LOD in VOCs monitoring. 

A turn-on type vapofluorochromic methoxybenzylidene methanone Schiff base applied to wearable VOC sensor and smartphone-based detection

This work presents the synthesis and photophysical properties of a vapoluminescent compound, (E)-1-(((4-(dimethylamino)phenyl)imino)methyl)naphthalen-2-ol (DPINO), and further studies its photophysical properties, mainly including twisted intramolecular charge transfer (TICT) and vapoluminescent behaviors. DPINO emits wreak fluorescence deposited on cellulose substrate, but exhibits a turn-on effect in response to various kinds of VOCs, showing fast response and high visual identification. Through spectral analysis, it is found that the physical interaction between DPINO and VOCs is influenced by multiple factors, including volatility, structural similarity and molecular size (steric hindrance), leading to varying degrees of fluorescence response toward different VOCs. Using RGB (red-green-blue) and CIE L*a*b* (CIELAB) color spaces, the output signals are well-quantified, deriving color shift (ΔE*) for sensitivity evaluation. And the limit of detection (LOD) is calculated to be 7.4 mg/m3 (2.22 ppm) and 2.4 mg/m3 (0.72 ppm), based on RGB and CIE L*a*b*, respectively. We further fabricated a bimolecular smart textile by dip-dyeing method, which includes the present DPINO as well as an inert luminogen MMA, i.e., fluorescent reference. The DPINO-MMA bimolecular smart textile can be freely designed in shape and size, and further made into smart clothes labels, e.g., chest card, arm band and wrist band. In scenario-based experiments, the smart textile shows notable turn-on fluorescence in response to VOCs, enabling high visual identification and real-time feedback. 

A vapofluorochromic dimethylaniline naphthol Schiff base used for fabricating smart textiles for VOCs detection

The development of fluorescent stimuli-responsive organic materials has attracted substantial interest due to their increasing optoelectronic applications. This study systematically introduces fluorine atoms on one end of carbazole-based N-salicylidene anilines 5a–5f to elucidate the impact in their solution and solid-state photophysics. The addition of fluorine atoms at one end of the molecule induced significant changes, for example, a reduction in the quantum yield (QY) fluorescence emission in solution, going from QY near unity in compound 5a (QY ∼ 100%) to a negligible emission in 5f (QY < 1%). Similarly, compound 5a showed a very strong aggregation-induced enhancement emission behavior, whereas compounds with a higher fluorine content were almost quenched. Furthermore, the crystalline solid-state photoisomerization in N-salicylidene anilines is not trivial, and only compounds with three (5e) and five fluorine atoms (5f) exhibited reversible solid-state photoisomerization under 405 nm light source irradiation. We propose that the presence of the arene-perfluoroarene interaction in the crystalline array facilitates the latter behavior. Our findings present a comprehensive study of crystal engineering for the obtention of photoswitchable crystalline materials and adjustable photophysics response, paving the way for its implementation in other systems.

Aggregation-Induced Emission Enhancement and Solid-State Photoswitching of Crystalline Carbazole N-Salicylidene Anilines

Excited-state intramolecular proton transfer (ESIPT)-triggered photochromic materials

A Target Recognition Matchin

Grayness correlation is a method with high reliability for target recognition. However, there is a lack of reliable guidelines for matching results. Basing on normalized correlation, this thesis uses the SURF (Speed up Robust Features) algorithm of local features of an image to verify matching results. By fully utilizing the global and local information of the image, this method ensures the reliability of the matching results. Emulation tests how that this method is hardly interfered by outside factors and can greatly save time by using parallel calculations. With a high accuracy of matching results, it is applicable for targets recognition.

A target recognition matching method with high reliability

Target recognition technology has been widely used in different areas around the world. Especially, target recognition technology developed for platforms such as satellite, unmanned reconnaissance plane, aircraft, etc. has been the focus of attention for various countries. Based on the features of image captured by reconnaissance aircraft, this thesis studies the image after-process methods and proposes a quick and effective target searching strategy.

A quick target recognition technology

A photochromic diethylamino methanone Schiff base with its application in color-shift-based binary data recording and information encryption-decryption

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A Target Recognition Matchin

A target recognition matching method with high reliability

A quick target recognition technology

A photochromic diethylamino methanone Schiff base with its application in color-shift-based binary data recording and information encryption-decryption