Figure 4 The mechanism investigation of the photooxidation stability of SFDBA crystal. The images of SFDBA crystal exposed to sunlight for different time intervals: a) 0 h under optical microscope; b) 2 h, c) 4 h, and d) 8h under fluorescence microscope. e) The possible oxidation intermediates and products during the self-sensitization process. f) Schematic illustration of the encapsulation strategy.
4e demonstrates that the sunlight-sensitive naphthylamines are under the protection of closely packed fluorenyl groups as a sterically hindered “armor”, so that the oxygen molecules cannot invade into the largest (100) plane but to attack the narrow lateral face. Further, the calculated Fukui electrophilic functions of the SFDBA molecule and its octamer indicate that the photooxidation active site is located on the acridine ring of the SFDBA molecule and is protected by the “armor” on the other side when the molecule aggregates (Figure S6 & S7). The low-dimensional morphology restricts the entrance of oxygen molecules, further minimizing the detrimental effect of photooxidation.
Conclusions
In conclusion, a self-encapsulation strategy is displayed by utilizing the ordered arranged stable part of the molecule to form an “armor” for the effective protection of active fragments away from oxygen. The molecular structure design, the molecular packing mode, and the low-dimensional crystal morphology are mutually connected and work together to promote the ultimate oxidative stability of SFDBA materials.
Experimental
Experimental Section. All of chemicals were purchased from J&K Scientific Co. Ltd., and were used without further purification unless otherwise stated.
Preparation of SFDBA micro/nano-crystals. The microcrystals of SFDBA were fabricated through reprecipitation method. Typically, 0.5 mg target compounds dissolved in 1 mL THF solution was injected into a 5 mL vigorously stirred water for 5 min, the sample was aging for about 24 h to stabilize the nanostructures. Subsequently, the microcrystals underwent centrifugation and were washed with pure water four times.
Preparation of SFDBA single crystals. Single crystals of SFDBA were obtained by the solvent diffusion methods, the growth conditions are manifested in Table S1. Crystallographic information is summarized in Table S2 (these data can also be obtained free of charge from the Cambridge Crystallographic Data Centre: 794132 (SFDBA).
Preparation of SFDBA dilute solution. A certain mass of SFDBA powder was added into 1 mL tetrahydrofuran solution to prepare a solution with a concentration of 10-3 mol/L, and then injected 30 μL the above solution into 3 mL tetrahydrofuran solution to obtain a dilute solution with a concentration of 10-5mol/L.
Preparation of SFDBA amorphous film. A quartz sheet with a size of 1.5*1.5 cm as the substrate was placed on the spin coater. The tetrahydrofuran solution of the SFDBA with a concentration of 5 mg/mL was dropped to the substrate. The spinning coating speed was 1200 rpm for 30 s, and the acceleration was 400 rpm/s.
Characterization Details. 1H NMR spectra were measured on a Varian Mercury Plus 400 spectrometer with tetramethylsilane as the internal standard. For scanning electron microscopic (SEM) studies, a drop of 15 μL target samples was precipitated on the silicon substrates with the solvent completely evaporated, and then the samples were examined with a field emission SEM (Hitachi S-4800) at an accelerating voltage of 5 kV. The transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) studies were performed in a JEM 2010F JEOL and operated at an accelerating voltage of 100kV. The single crystal data collection was performed at around 100 or 298 K on a Bruker 2000 CCD area detector using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). All structures were solved by direct methods using SHELXS-2015 and refined against F2 using SHELXL-2015. X-ray diffraction (XRD) patterns were performed on a Bruker D8 X-ray diffractometer with Cu KR radiation (λ = 1.54050 Å). The operating 2θ angle ranges from 5 to 30˚, with the step length of 0.025˚. Photoluminescence (PL) emission spectra was measured using a PerkinElmer LS55 spectrophotometer. Photoluminescence quantum efficiency (PLQY) and fluorescence decay curves were measured using a steady/transient fluorescence spectrometer (FLS 920). Fourier transform infrared (FT-IR) spectra was obtained by a PerkinElmer Spectrum Two FTIR spectrometer. The luminescence imaging was taken by Olympus IX71 inverted fluorescence microscope. All the theoretical calculations were performed by using the B3LYP functional with the 6-31G(d) basis set based on their crystallographic data.
Supporting Information
The supporting information for this article is available on the WWW under https://doi.org/10.1002/cjoc.2023xxxxx.
Acknowledgement
This work was supported by the Funded by Natural Science Foundation of Nanjing University of Posts and Telecommunications (NY222157, NY221085), State Key Laboratory of Organic Electronics and Information Display (GZR2022010008),Key Laboratory of Low-dimensional Materials Chemistry of Jiangsu Province (JSKC20022), General Program of China Postdoctoral Science Foundation (2022M711684), General Program of Basic Science (Natural Science) of Colleges and Universities of Jiangsu Province (22KJB430036), National Overseas Study Fund (202008320051), National Key Laboratory (2009DS690095), and the National Natural Science Foundation of China (62288102).
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