A Simple Approach to Achieve Organic Radicals with Unusual Solid-State Emission and Persistent Stability

Open AccessCCS ChemistryCOMMUNICATION6 Jun 2022A Simple Approach to Achieve Organic Radicals with Unusual Solid-State Emission and Persistent Stability Xueqian Zhao†, Junyi Gong†, Parvej Alam, Chao Ma, Yanpei Wang, Jing Guo, Zebin Zeng, Zikai He, Herman H. Y. Sung, Ian D. Williams, Kam Sing Wong, Sijie Chen, Jacky W. Lam, Zheng Zhao Ben Zhong Tang Zhao† Department of Chemistry, Hong Kong Branch Chinese National Engineering Research Center for Tissue Restoration Reconstruction, Institute Advanced Study Guangdong-Hong Kong-Macro Joint Laboratory Optoelectronic Magnetic Functional Materials, University Science Technology, Clear Water Bay, Kowloon, 999077 †X. J. Gong contributed equally this work.Google Scholar More articles by author , Gong† Alam Google Ma Physics, Wang State Key Chemo/Biosensing Chemometrics, College Chemistry Chemical Engineering, Hunan University, Changsha, Province 410082 Guo Zeng He School Science, Harbin Shenzhen, HIT Campus Town, Guangdong 518055 Sung Williams Wong Chen Ming Wai Lau Centre Reparative Medicine, Karolinska Institutet, Lam *Corresponding authors: E-mail Address: [email protected] Kong, 518172 HKUST-Shenzhen Institute, South Area Hi-Tech Park, Nanshan, 518057 Aggregation-Induced Emission, SCUT-HKUST Luminescent Materials Devices, China Guangzhou, 510640 AIE Guangzhou Development District, Huangpu, 510530 https://doi.org/10.31635/ccschem.021.202101192 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Stable organic radicals are promising materials information storage, molecular magnetism, electronic devices, biological probes. Many have been prepared, but most non- or weakly emissive degrade easily upon photoexcitation. It remains challenging produce stable efficient luminescent because the absence general guidelines their synthesis. Herein, we present a photoactivation approach generate radical from tris(4-chlorophenyl)phosphine (TCPP) red emission in crystal state. The mechanistic study suggests that symmetry breaking causes changes conformation, redox properties, packing facilitates generation stabilization. This design strategy demonstrates straightforward develop will open new doors photoinduced materials. Download figure PowerPoint Introduction doublet emitters next-generation luminophores which originates radiative decay unusual lowest excited state (D1) ground (D0).1–3 Their potential applications in, example, light-emitting diodes (OLEDs),4 light sources,5 chemical sensors explored.6–8 Recently, it has demonstrated can achieve upper limit (100%) internal quantum efficiency OLEDs due nature.9,10 Thus, practical attracted considerable attention last decade brought research field back life. Thanks extensive efforts scientists, several radicals, such as tris-2,4,6-trichlorophenylmethyl,11 perchlorotriphenylmethyl,12 biphenylmethyl,7,13–15 successfully developed luminous cores exploiting steric delocalization effects. In addition, strategies modification,16–18 physical doping,19 even supramolecular assembly20–23 utilized improve stability luminescence yield (QY). spite gratifying progress, species showing strong still relatively rare mainly limited triarylmethyl radicals.8,24–27 On other hand, similar many conventional luminophores, exhibit low at high solution concentrations solid aggregation-caused quenching effect,28 problem must be solved thin films aggregates widely applications. However, on is preliminary stage. Besides, generated time-consuming As result, development methods also exciting meaningful. work, demonstrate crystals ambient conditions. Figure 1a shows schematic diagram process. X-ray crystallographic analysis combined density functional theory (DFT) calculations reveal TCPP UV irradiation results charge separation, serves driving force solid-state radicals. persistent show an half-life over one week when stored Interestingly, quenched only destroying irradiating visible light, suggesting acts protective cage stabilize formed After recrystallization, sample regenerate again exposure. Taking advantage reversible feature generation, photocontrollable anticounterfeiting film was demonstrated. Although there some achievements generating wet chemistry reactions, synthesis any external additives highly desirable. current work may up avenue achieving photoresponsive Results Discussion purchased commercial source purified multiple column chromatography followed recrystallization three times dichloromethane hexane mixture before use. structure confirmed NMR spectroscopies high-resolution mass spectrometry (HRMS) well single-crystal crystallography ( Supporting Information Figures S1–S4). final products appeared colorless both were almost nonemissive S5). UV–vis spectrum exhibited absorption band centered around 250 nm, consistent its appearance (Figure 1b). 365-nm few seconds, gradually turned orange. Two peaks 496 520 nm suggestive narrow gaps. triphenylphosphine derivatives electron-rich, they lose electrons readily during oxidation process oxidized oxides, homocoupling products. These often redder than neutral counterparts.29–31 To verify origin photogenerated species, high-performance liquid (HPLC) 31P carried out. signals retention time 2.3 min shift 27.2 good agreement those oxide S6). pure found rather speculated orange color hypothesis, electron paramagnetic resonance (EPR) spectroscopy out indicated i-TCPP (irradiated TCPP) signal g value 2.0035. pristine silent 1c). We protect inside core not surface. Hence, trace amount reaction oxygen. Therefore, these indicate photoirradiation core. three-dimensional image reconstruction crystalline confocal microscopy existence S7). showed bright 620 QY 4.6%, great contrast characteristic (QY < 0.1%) toluene 1d). typical behavior luminogens aggregation-induced emission,32–34 aggregate weak no S8). photoluminescence (PL) lifetime measured 3.9 ns, fluorescent nature 1e). elucidate emission, further detailed investigation photophysical property conducted. Because impurity amounts exert influence property,35,36 purity HPLC elemental (EA). difference between obtained EA theoretical <0.3% molecule S6a). Different batches samples different sources through same procedure. Despite fact varied all identical optical properties demonstrative excellent data reproducibility reliability S9). now clear red-emitting under photoirradiation. after 0.1%), formation. Notably, along EPR disappears grinding S10). observation supports significance where lattice water atmospheric 1 | (a) Schematic (b) spectra, (c) (d) PL spectra exposure seconds room temperature, ?ex = 365 nm. insets photographs changes, yield. (e) Time-resolved curves ?max 400 understand mechanism analyzed TCPP’s stacking. Single-crystal 2a Table S1) indicates adopts D2h commonly observed C3 analogs like S2). dihedral angles phenyl rings identical. particular, (87.6°) pair (R2–R2?) much larger others (66.4° 50.8°). Another structural ring (R1) parallel lone phosphorus atom. optimized gas phase equal. leads conformation state, first noticed described “abnormal” Bin Shawkataly et al. 1996.37 donor–acceptor structure, DFT based point group distinct separation highest occupied orbital (HOMO) located phosphorous atom plane. unoccupied (LUMO) two vertical No HOMO LUMO 2b). worth noting molecules transfer (PET) transient, sensitive, quickly react oxygen lowers contrary, conditions, correlated asymmetric conformations structures. Further adopt alternate intermolecular arrangement closest distance about 3.29 Å, beneficial exciton stabilization hopping 2c). consideration within caused unique breaking, propose PET 2d).22,38–40 2 Molecular using BLYP/def2-SVP (top) (bottom) thermal ellipsoids 50% probability. Hydrogen atoms omitted clarity. Electron cloud distributions states calculated TD-DFT M062X/def2-TZVP, ORCA 4.1 program. Crystal diagrams TCPP. Proposed single-electron confirm rationality our calculation high-precision double-hybrid PWPB95 def2-TZVP basis set. free energy dimer (cations anions) 3a). cations anions lower formation thermodynamically favorable. configuration anion crystal, belong 3b S3). mentioning despite very crowded stacked interaction, CH···? exists structure. responsible radicals.41,42 spin distribution 3c). For cation, unpaired distributed benzene ring, principal anion, Such suggest heterogenous instead homogenous, complex hyperfine splitting pattern spectrum. simulated time-dependent (TD)-DFT (Figures 3d 3e). superimposed cation 457 482 correlate experimental results. Furthermore, in-depth arise HOMO–9?singly (SOMO) transition SOMO?LUMO+7 respectively 3d). level wave functions frontier orbitals shown S11. structures M062X/def2-TZVP bands 549 667 oscillator strengths 0.021 (SOMO, LUMO+7) 0.105 (HOMO-4, SOMO), S4 S12). cations, excitation S13). 3 profile PWPB95/def2-TZVP. BLYP/def2-SVP. single (SP) M062X/def2-TZVP. (d–e) Absorption PBE0/def2-TZVP phase. enables serve material reporter evaluate visualization method measuring change time. 4a, placed conditions without protection, machine intervals survive more re-photoirradiation “on–off” repeated technically feasible 4b). 4 Plots relative intensity condition (365 nm) (520 irradiation. TCPP-loaded filter paper pressure responsiveness makes possible utilize smart responsive photopatterning 5a 5b). By immersing TCPP, prepared. stamping freshly soaked seal character “?” then patterned area while rest autofluorescence. could erased green lamp nm). Since speculate exerting induce microcrystals paper. 5 Preparation (Tang). fluorescence images acquired (254 (using 520-nm infrared semiconductor laser). Scale bar: 0.5 cm. Conclusion reported. A reveals crystals, ascribed cation. Theoretical integrated photoredox facilitating PET. protects endow possibility in-situ assistance window producing being explored. Footnote CCDC 2080878 contains supplementary TCPP.37 Cambridge Crystallographic Data (see www.ccdc.cam.ac.uk). available includes methods, characterizations, calculations, data, imaging data. Conflicts Interest There conflicts declare. Funding project financially supported Natural Foundation (grant no. 21788102), nos. 2019B121205002 2019B030301003), Grants Council 16305618, 16305518, C6014-20W, C6009-17G, AoE/P-02/12), Program 2018YFE0190200), Innovation Technology Commission ITC-CNERC14SC01), Plan Shenzhen JCYJ20180306174910791, JCYJ20170818113530705, JCYJ20170818113538482, JCYJ20160229205601482). Preprint Acknowledgment presented article posted preprint server prior publication CCS Chemistry. corresponding here: DOI: 10.26434/chemrxiv.12479321.v1 Acknowledgments gratefully acknowledge contributions Lili Du PHILLIPS, David Lee (HKU), Zhijiao Congwu Ge Xike Gao Shanghai (SIOC) Academy Sciences (CAS), Qiang Wei Ningbo Industrial (CNITECH), Xing Feng Ruoyao Zhang measurements. 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