English

• Azulene has emerged as a promising candidate for constructing advanced organic optoelectronic materials due to its unique optoelectronic properties [1-6]. In recent years, azulene-based materials have been extensively investigated in organic field-effect transistors (OFETs), solar cells, and other related applications [7-14]. As illustrated in Figs. 1a and b, the asymmetric frontier molecular orbitals (FMO) of azulene reduce electron repulsion between unpaired electrons, resulting in a narrow energy gap between its ground state (S₀) and first excited state (S₁). This reduced energy gap leads to a visible-range absorption band (S₀ → S₁ transition), endowing azulene with its characteristic blue color [15-17]. Furthermore, the significant energy difference between S₁ and S₂ (∆E(S₂-S₁) > 10,000 cm⁻¹) coupled with orbital asymmetry slows the non-radiative S₂ → S₁ transition while enhancing the radiative S₂ → S₀ pathway. This gives rise to the anti-Kasha fluorescence behavior observed in azulene [18,19]. However, this unique photophysical property also confines the fluorescence of azulene and its derivatives to the short-wavelength region with inherently weak emission intensities [20-25]. For example, the reported azulene-based BN-heteroaromatics exhibit photoluminescence quantum yield (PLQY) of less than 0.5% (Fig. S1a in Supporting information) [24].

  Figure 1

  

  Figure 1.  (a) Chemical structures and schematic diagrams of radiation transitions for azulene and 1-azaazulene. (b) Frontier molecular orbitals and their energetics of azulene and 1-azaazulene. (c) Chemical structures, emission peaks, and photoluminescence quantum yields of the 1-azaazulene-based BF₂ complex.

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  As illustrated in Fig. 1a, replacement of the CH moiety at the 1-position of azulene with a N atom yields its heteroanalog, 1-azaazulene. Density functional theory (DFT) calculations demonstrate that N substitution profoundly alters the electronic structure and FMO energetics (Fig. 1b). Compared to pristine azulene (HOMO/LUMO = −5.20/−1.82 eV, E_gap = 3.38 eV), 1-azaazulene exhibits stabilized HOMO (−5.93 eV) and LUMO (−2.16 eV) levels, with the bandgap widening to 3.77 eV due to a more pronounced stabilization of the HOMO level. Time-dependent DFT (TD-DFT) calculations reveal that while 1-azaazulene retains asymmetric frontier orbitals, the S₀-S₁ energy gap becomes substantially wider than that of the azulene. Notably, the reduced S₂-S₁ energy separation accelerates the non-radiative S₂ → S₁ conversion compared to azulene, effectively suppressing the anti-Kasha S₂ → S₀ radiative transition. Such changes in electronic structure and FMO energetics render 1-azaazulene a promising scaffold for designing Kasha-compliant fluorescent materials with red-shifted emission profiles compared to its quinoline isomer (Fig. S2 in Supporting information) [26-29].

  Boron difluoride (BF₂) complexes represent a prominent class of luminescent materials [30-35]. The lone pair electrons on the N atom of 1-azaazulene enable effective coordination, making it an ideal ligand for constructing BF₂ complexes [36-40]. In this study, four asymmetric 1-azaazulene-based BF₂ complexes (Ph-NN, Ph-ON, Ca-NN, and Py-NN, Fig. 1c) were designed, synthesized, and systematically investigated for their photophysical properties. The luminescence wavelength and efficiency of these complexes were modulated by structural variations in the ancillary coordination groups. In contrast to the anti-Kasha fluorescence observed in azulene derivatives, all four 1-azaazulene constructs display S₁ → S₀ emission fluorescence. Ph-NN exhibits an emission peak at 705 nm, while Py-NN achieves a PLQY of 19.3%. Furthermore, the organic light-emitting diode (OLED) fabricated with Py-NN as the emitter via a sensitization strategy delivers a maximum external quantum efficiency (EQE_max) of 3%.

  The synthetic routes for Ph-NN, Ph-ON, Ca-NN, and Py-NN are illustrated in Scheme 1. First, 2-chloro-1-azaazulene (S1) was synthesized according to the literature procedure [41,42]. Subsequently, Suzuki-Miyaura coupling reactions between S1 and various arylboronic acids S2a-S2d were performed, affording intermediates S3a-S3d in 67%-85% yields. Notably, for reaction of S1 and S2d, treatment with sodium methoxide during workup enabled in situ deprotection of the Boc group, directly affording intermediate S3d. To prevent potential interference of the amino group during BF₂ complex formation, S3a was substituted with an alkyl chain to obtain intermediate S4a. Finally, exposure of intermediates S4a and S3b-d to excess BF₃·Et₂O in toluene, in the presence of TEA/DIPEA, afforded 1-azaazulene-based BF₂ complexes Ph-NN, Ph-ON, Ca-NN, and Py-NN with 50%-62% yields. These compounds were characterized by nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HRMS). The full characterization data can be found in Supporting information.

  Scheme 1

  

  Scheme 1.  Synthesis route for Ph-NN, Ph-ON, Ca-NN, and Py-NN. (ⅰ) Pd(PPh₃)₄, K₂CO₃, THF, H₂O, 80–110 ℃; (ⅱ) C₄H₉Br, n-BuLi, THF, −78~35 ℃; (ⅲ) BF₃·Et₂O, EtN₃/DIPEA, toluene, 35–80 ℃.

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  The structures of Ph-NN, Ph-ON, Ca-NN, and Py-NN were further confirmed through X-ray single crystal analysis (Fig. 2, Tables S1-S4 in Supporting information). The single-crystal structures reveal that all four compounds possess highly planar backbones, with the largest dihedral angles in the fused rings being less than 4.95° (Fig. S3 in Supporting information). The crystal packing diagrams in Fig. 2 and Figs. S4-S7 (Supporting information) demonstrate that in Ph-NN, Ph-ON, Ca-NN, and Py-NN, adjacent molecules are arranged through antiparallel stacking of their conjugated backbones. The stacking distances, ranging from 3.32 Å to 3.47 Å, suggest that all four molecules have strong π-π interactions. These pronounced π-π interactions lead to a decrease in the PLQY of the thin films due to aggregation-caused quenching (ACQ) effects (Table S5 in Supporting information). As shown in Fig. S3, in the four BF₂ complexes, the average bond lengths (1.38–1.42 Å) of the 1-azaazulene and its connected aromatic rings are close to the bond length of aromatic C=C bonds, indicating that the ligand backbones maintain good aromaticity. The NICS(1)_zz values (Fig. S8 in Supporting information) and the anisotropy of the induced current density (AICD) plots (Fig. S9 in Supporting information) further confirm the aromatic characteristics of the 1-azaazulene-based ligand backbones. Notably, the N→B coordination bonds in these four molecules (1.55–1.58 Å) are significantly shorter than those reported in asymmetric BF₂ complexes [43,44]. The short N→B bond lengths reflect strong dative interactions between nitrogen and boron, enhancing the complex’s stability and ensuring the integrity of the fluorescent materials under various conditions.

  Figure 2

  

  Figure 2.  Crystal structures and packing diagrams of (a) Ph-NN, (b) Ph-ON, (c) Ca-NN, and (d) Py-NN.

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  To investigate the photophysical properties of Ph-NN, Ph-ON, Ca-NN, and Py-NN, we performed absorption spectroscopy, steady-state, and time-resolved emission spectroscopy under oxygen-free conditions at a concentration of 1 × 10⁻⁵ mol/L (Table 1). As shown in Fig. 3a, all four molecules exhibit intense absorption bands in the 300–400 nm range, primarily attributed to S₀ → S₂ transitions of 1-azaazulene units. However, they exhibit distinct absorption differences in the long-wavelength region. Ph-ON and Py-NN display maximum absorption peaks at 487 and 501 nm, respectively, with pronounced shoulder peaks, indicating dominant localized excitations. In contrast, Ph-NN and Ca-NN show significantly red-shifted absorption at 597 and 555 nm, accompanied by broader absorption bands lacking distinct shoulders, which suggests excitations with pronounced charge-transfer (CT) characteristics. Notably, these absorption bands display significant redshifts compared to analogous quinoline derivatives [43,45,46], which may originate from the asymmetric electron distribution and narrower FMO energy gaps of the 1-azaazulene core. Remarkably, the molar absorption coefficients for the S₀ → S₁ transitions of these compounds (ε > 10⁴ L mol⁻¹ cm⁻¹) are substantially higher than those of typical azulene-based molecules (ε < 10⁴ L mol⁻¹ cm⁻¹).

  Table 1

  

  Table 1.  Summarized key photophysical properties of compounds Ph-NN, Ph-ON, Ca-NN, and Py-NN.

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  Comp.	λabs (nm)a	λem (nm)a	ΦPL (%)a	τ (ns)a	kr (107 s−1)b	knr (109 s−1)c
  Ph-NN	597	705	0.3	0.18	1.67	5.54
  Ph-ON	487	552	2.9	0.84	3.45	1.16
  Ca-NN	555	653	2.1	0.59	3.56	1.66
  Py-NN	501	560	19.3	2.03	9.51	0.40
  a Meassured in oxygen-free toluene solution (1 × 10−5 mol/L) at room temperature; b Radiative rate constant is calculated as kr =ΦPL/τ; c Non-radiative rate constant is calculated as knr = (1 − ΦPL)/τ.

  Figure 3

  

  Figure 3.  (a) UV–vis absorption and (b) emission of compounds Ph-NN, Ph-ON, Ca-NN, and Py-NN (10⁻⁵ mol/L in oxygen-free toluene) with pictures inserted.

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  As depicted in Fig. 3b, Ph-NN exhibits an S₁ → S₀ emission peak at 705 nm, a rare feature among small-molecule BF₂ complexes, with a Stokes shift (S) of 108 nm. However, its PLQY is only 0.3%, likely due to ultrafast nonradiative decay. Time-resolved emission spectroscopy (Fig. S10a in Supporting information) reveals an exceptionally short luminescence lifetime (τ) of 0.18 ns for Ph-NN, yielding a radiative transition rate (k_r) of 1.67 × 10⁷ s⁻¹ and a nonradiative rate (k_nr) of 5.54 × 10⁹ s⁻¹ (Table 1). In contrast, Ph-ON and Ca-NN display blue-shifted emission peaks at 552 nm (S = 74 nm) and 653 nm (S = 98 nm), with improved PLQYs of 2.9% and 2.1%, respectively. Their luminescence lifetimes increase to 0.84 ns (Ph-ON) and 0.59 ns (Ca-NN), corresponding to k_r/k_nr values of 3.45 × 10⁷ s⁻¹/1.16 × 10⁹ s⁻¹ and 3.56 × 10⁷ s⁻¹/1.66 × 10⁹ s⁻¹ (Figs. S10b and c in Supporting information). Their enhanced PLQYs arise from both increased k_r and reduced k_nr. Significantly, Py-NN demonstrates the highest luminescence efficiency among the four 1-azaazulene-based BF₂ complexes, exhibiting an emission peak at 560 nm (S = 59 nm) with a PLQY of 19.3%. The relatively small Stokes shift and high emission efficiency suggest dominant localized-state emission in Py-NN. Time-resolved photoluminescence spectrum (Fig. S10d in Supporting information) confirms a prolonged luminescence lifetime of 2.03 ns, corresponding to k_r = 9.51 × 10⁷ s⁻¹ and k_nr = 0.40 × 10⁹ s⁻¹. These results indicate that by altering the structure of the groups attached to the 1-azaazulene, it is possible to tune the photophysical properties including absorption spectrum, emission spectrum, and emission efficiency of 1-azaazulene-based BF₂ complexes.

  DFT calculations at the B3LYP/6–31G+(d,p) level were employed to investigate the electronic properties of the four 1-azaazulene-based BF₂ complexes, with the calculated data summarized in Table S6 (Supporting information). As illustrated in Fig. 4, the FMO of Ph-NN, Ph-ON, Ca-NN, and Py-NN exhibit significantly uneven electron density distributions, a notable contrast to most BF₂ complexes [47-49]. Specifically, the LUMO electron density is primarily distributed over the 1-azaazulene unit, while the HOMO electron density is mainly localized on the aniline, phenol, carbazole, and pyrrole moieties. For Ph-ON and Py-NN, especially the latter, the HOMO electron density also has a small distribution on the 1-azaazulene. This pronounced asymmetry in molecular orbital distribution suggests a propensity for charge-transfer (CT) transition absorption in these compounds, while Ph-ON and Py-NN may also exhibit localized transition absorption. As shown in Fig. 4, the calculations indicate that by altering the structure of the group connected to the 1-azaazulene, the FMO energetics and band gap of the 1-azaazulene-based BF₂ complexes can be effectively modulated, thereby tuning the absorption and emission wavelengths of the molecules.

  Figure 4

  

  Figure 4.  Frontier molecular orbitals, and their energetics of compounds Ph-NN, Ph-ON, Ca-NN, and Py-NN, obtained by DFT and TD-DFT calculations.

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  Since the B3LYP functional may underestimate the energy of charge-transfer electronic states [50], the long-range corrected M062X functional was employed to study the excited states of 1-azaazulene-based BF₂ complexes using the 6–31G(d) basis set. TD-DFT calculations show that the oscillator strengths (f) for the S₀ → S₁ transition of Ph-NN, Ph-ON, Ca-NN, and Py-NN are 0.3299, 0.3009, 0.3458, and 0.4973, respectively. The increased f could originate from the superior hole-electron overlap of S₁ state of Py-NN compared with the other three molecules. This indicates that Py-NN likely exhibits accelerated radiative decay rate (k_r). In addition, Py-NN demonstrated a relatively large energy gap (ΔE = 2.75 eV) and smallest reorganization energy (λ_M = 3942 cm⁻¹), which is conducive to decelerating nonradiative decay rate (see Supporting information for details). Accordingly, Py-NN with large k_r and small k_nr likely exhibits high PLQY, which agrees well with the experimental results. In the electron-hole overlap maps of the S₁ excited state and atomic transition density matrix (TDM) heat maps for the S₀ → S₁ transition (Fig. S10e in Supporting information), Ph-ON and Py-NN show substantial electron-hole overlap, primarily localized on the 1-azaazulene unit. This localization is favorable for the formation of localized excited states (LE). Additionally, the maps demonstrate that the electronic excitation process is chiefly focused on electron transfer among the atoms within the 1-azaazulene unit.

  Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) tests were performed on Ph-NN, Ph-ON, Ca-NN, and Py-NN, as shown in Figs. S11a-d and Table S8 (Supporting information). Electrochemical calculations determined the HOMO/LUMO levels of Ph-NN, Ph-ON, Ca-NN, and Py-NN to be −5.39/−3.61 eV, −6.39/−3.57 eV, −5.42/−3.70 eV, and −5.73/−3.63 eV, respectively. Overall, the FMO energy levels obtained from electrochemical measurements, particularly the HOMO levels, were consistent with the theoretical computational trends. Additionally, thermogravimetric analysis (TGA) was conducted and the results indicated that the thermal decomposition temperatures (T_d) for Ph-NN, Ph-ON, Ca-NN, and Py-NN were 273, 246, 371, and 428 ℃ (Fig. S12 in Supporting information), respectively, demonstrating good thermal stability across all compounds.

  Owing to the moderate PLQY and superior thermal stability of Py-NN, OLED devices were fabricated to evaluate the electroluminescent performance of 1-azaazulene-based BF₂ complexes with multilayer configurations of ITO/HATCN (5 nm, hole injection layer)/NPB (40 nm, hole-transport layer)/TCTA (10 nm, exciton-blocking layer)/TPBi: 20 wt% thermally activated delayed fluorescence sensitizer 4CZIPN and 1 wt% Py-NN (30 nm, emissive layer)/TPBi (25 nm, electron-transport layer)/LiF (1 nm, electron-injection layer)/Al (150 nm) (Fig. 5a and Fig. S12). As shown in Fig. 5b, the device exhibits strong orange emission with the corresponding electroluminescence peak value (λ_em) located at 565 nm, which is close to the photoluminescnece peak of Py-NN. And the OLED exhibited an EQE_max of 3.0% and a turn-on voltage of 5.2 V.

  Figure 5

  

  Figure 5.  (a) OLED device architecture. (b) Electroluminescent emission spectrum at 6 V. (c) The J–V–L (current density–voltage–luminance) characteristics. (d) The EQE–J (external quantum efficiency–current density) relationship.

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  In summary, this study successfully designed and synthesized four asymmetric 1-azaazulene-based BF₂ complexes (Ph-NN, Ph-ON, Ca-NN, and Py-NN) to explore their optoelectronic properties. By modifying ancillary coordination groups, the FMO energetics and band gaps of these complexes were effectively tuned, allowing adjustments in their absorption and emission properties. All four 1-azaazulene constructs exhibit S₁ → S₀ emission fluorescence, in contrast to azulene derivatives, which typically display anti-Kasha fluorescence and low PLQY. Notably, Py-NN demonstrated superior performance, achieving a PLQY of 19.3% with an emission peak at 560 nm. This enhancement is attributed to improved HOMO-LUMO overlap and suppressed nonradiative decay pathways. OLEDs incorporating Py-NN as an emissive dopant exhibited a maximum EQE of 3%, underscoring its electroluminescent potential. These findings demonstrate that 1-azaazulene serves as a promising scaffold for developing fluorescent materials, overcoming the inherent limitations of traditional azulene derivatives and advancing its potential applications in optoelectronic devices. Moreover, 1-azaazulene constructs possess smaller band gaps compared to traditional fluorescent materials with similar-sized π-conjugated systems. This characteristic facilitates the development of long-wavelength emission fluorescent materials, which are desirable for applications requiring deep-red or near-infrared emission.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Zijian Zhang: Writing – original draft, Formal analysis, Data curation. Fangxin Du: Writing – original draft, Methodology, Formal analysis. Lijia Liu: Formal analysis, Data curation. Yixiang Sun: Formal analysis. Jie Xue: Writing – review & editing, Methodology, Investigation. Hanshen Xin: Writing – review & editing, Writing – original draft, Project administration, Investigation, Funding acquisition, Conceptualization.

  Acknowledgments

  This research was financially supported by the Natural Science Foundation of Shanghai Municipality (No. 25ZR1402168), the National Natural Science Foundation of China (No. 22101170) and Shanghai University. We thank Wen-wen Zhang and Jinheng Pan (Mass Spectrometry & Metabolomics Core Facility of Westlake University) for MS analysis.

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2025.111987.

  
  
• 1. [1]

     A. Ong, T. Tao, Q. Jiang, et al., Angew. Chem. Int. Ed. 61 (2022) e202209286. doi: 10.1002/anie.202209286

  2. [2]

     H. Xin, B. Hou, X. Gao, Acc. Chem. Res. 54 (2021) 1737–1753. doi: 10.1021/acs.accounts.0c00893

  3. [3]

     J. Huang, S. Huang, Y. Zhao, et al., Small Methods 4 (2020) 2000628. doi: 10.1002/smtd.202000628

  4. [4]

     J.X. Dong, H.L. Zhang, Chin. Chem. Lett. 27 (2016) 1097–1104. doi: 10.1016/j.cclet.2016.05.005

  5. [5]

     Y. He, Y. Zhu, M. Luo, H. Xia, Chin. Chem. Lett. 36 (2025) 110463. doi: 10.1016/j.cclet.2024.110463

  6. [6]

     B. Yu, P. Du, J. Guo, H. Xin, J. Zhang, Chin. Chem. Lett. 35 (2024) 109321. doi: 10.1016/j.cclet.2023.109321

  7. [7]

     L. Zhou, F. Qiu, Y. Ding, et al., Angew. Chem. Int. Ed. 63 (2024) e202409750. doi: 10.1002/anie.202409750

  8. [8]

     H. Xin, C. Ge, X. Jiao, et al., Angew. Chem. Int. Ed. 57 (2017) 1322–1326.

  9. [9]

     M. Murai, S. Iba, S. Hamao, et al., Bull. Chem. Soc. Jpn. 96 (2023) 1077–1081. doi: 10.1246/bcsj.20230155

  10. [10]

      J. Wen, F. du, B. Yu, Chem. Sci. 15 (2024) 12589–12597. doi: 10.1039/D4SC02566K

  11. [11]

      H. Nishimura, N. Ishida, A. Shimazaki, et al., J. Am. Chem. Soc. 137 (2015) 15656–15659. doi: 10.1021/jacs.5b11008

  12. [12]

      C. Zhang, Y. Kong, J. Xiang, et al., Chem. Sci. 16 (2025) 1353–1363. doi: 10.1039/D4SC06614F

  13. [13]

      G. Yang, S. Sangtarash, Z. Liu, et al., Chem. Sci. 8 (2017) 7505–7509. doi: 10.1039/C7SC01014A

  14. [14]

      X. Fu, H. Han, D. Zhang, et al., Chem. Sci. 11 (2020) 5565–5571. doi: 10.1039/d0sc00770f

  15. [15]

      M. Beer, H.C. Longuet-Higgins, J. Chem. Phys. 23 (1955) 1390–1391. doi: 10.1063/1.1742314

  16. [16]

      M. Kasha, Discuss. Faraday Soc. 9 (1950) 9–14.

  17. [17]

      J. Michl, E.W. Thulstrup, Tetrahedron 32 (1976) 205–209. doi: 10.1016/0040-4020(76)87002-0

  18. [18]

      D. Dunlop, L. Ludvíková, A. Banerjee, H. Ottosson, T. Slanina, J. Am. Chem. Soc. 145 (2023) 21569–21575. doi: 10.1021/jacs.3c07625

  19. [19]

      R. Pino-Rios, R. Báez-Grez, D.W. Szczepanik, M. Solá, Phys. Chem. Chem. Phys. 26 (2024) 15386–15392. doi: 10.1039/d4cp01284d

  20. [20]

      N. Tetreault, R.S. Muthyala, R.S.H. Liu, R.P. Steer, J. Phys. Chem. A 103 (1999) 2524–2531. doi: 10.1021/jp984407q

  21. [21]

      H. Yamaguchi, S. Sato, M. Yasunam, T. Sato, M. Yoshinobu, Spectrochim. Acta A 53 (1997) 2471–2473. doi: 10.1016/S1386-1425(97)00151-0

  22. [22]

      O.K. AbouZied, H.K. Sinha, R.P. Steer, J. Mol. Spectrosc. 183 (1996) 42–56.

  23. [23]

      H. Yamaguchi, S. Sato, M. Yasunam, T. Sato, M. Yoshinobu, Spectrochim. Acta A 53 (1997) 2471–2473. doi: 10.1016/S1386-1425(97)00151-0

  24. [24]

      H. Xin, J. Li, X. Yang, X. Gao, J. Org. Chem. 85 (2019) 70–78.

  25. [25]

      J. Zhao, H. Huang, N. Li, et al., Tetrahedron 144 (2023) 133581. doi: 10.1016/j.tet.2023.133581

  26. [26]

      S.H. El-Demerdash, S.A. Halim, A.M. El-Nahas, A.B. El-Meligy, Sci. Rep. 13 (2023) 15626. doi: 10.1038/s41598-023-42450-1

  27. [27]

      S.A. Halim, A.B. El-Meligy, A.M. El-Nahas, S.H. El-Demerdash, Sci. Rep. 14 (2024) 219. doi: 10.1038/s41598-023-50660-w

  28. [28]

      A.B. El-Meligy, S.H. El-Demerdash, M.A. Abdel-Rahman, et al., ACS Omega 7 (2022) 14222–14238. doi: 10.1021/acsomega.2c00866

  29. [29]

      Y.Q. Zhang, C.C. Yang, J.Y. Ma, W.Q. Tian, Chem. Sci. 15 (2024) 2100–2111. doi: 10.1039/d3sc04443b

  30. [30]

      A. Loudet, K. Burgess, Chem. Rev. 107 (2007) 4891–4932. doi: 10.1021/cr078381n

  31. [31]

      D. Wang, X. Wang, S. Zhou, et al., Coord. Chem. Rev. 482 (2023) 215074. doi: 10.1016/j.ccr.2023.215074

  32. [32]

      M. Poddar, R. Misra, Coord. Chem. Rev. 421 (2020) 213462. doi: 10.1016/j.ccr.2020.213462

  33. [33]

      G. Ulrich, R. Ziessel, A. Harriman, Angew. Chem. Int. Ed. 47 (2008) 1184–1201. doi: 10.1002/anie.200702070

  34. [34]

      Z. Shi, X. Han, W. Hu, et al., Chem. Soc. Rev. 49 (2020) 7533–7567. doi: 10.1039/d0cs00234h

  35. [35]

      J. Wang, Q. Gong, L. Jiao, E. Hao, Coord. Chem. Rev. 496 (2023) 215367. doi: 10.1016/j.ccr.2023.215367

  36. [36]

      X. Shao, M. Liu, J. Liu, L. Wang, Angew. Chem. Int. Ed. 61 (2022) e202205893. doi: 10.1002/anie.202205893

  37. [37]

      J. Wakabayashi, M. Gon, K. Tanaka, Y. Chujo, Macromolecules 53 (2020) 4524–4532. doi: 10.1021/acs.macromol.0c00745

  38. [38]

      Y. Cao, C. Zhu, M. Barłóg, et al., J. Org. Chem. 86 (2021) 2100–2106. doi: 10.1021/acs.joc.0c02052

  39. [39]

      M. Zhao, Z. Yuan, Y. Zhou, Org. Lett. 26 (2024) 8837–8841. doi: 10.1021/acs.orglett.4c03270

  40. [40]

      F. Yang, F. Ren, X. Liu, M. Zhao, Y. Zhou, Asian J. Org. Chem. 14 (2025) e202400804. doi: 10.1002/ajoc.202400804

  41. [41]

      T. Nozoe, S. Seto, S. Matsumura, T. Asano, Proc. Jpn. Acad. 32 (1956) 339–343. doi: 10.2183/pjab1945.32.339

  42. [42]

      K. Yukio, K. Masaji, J. Am. Chem. Soc. 79 (1957) 5460–5463. doi: 10.1021/ja01577a035

  43. [43]

      T. Nakano, A. Sumida, K. Naka, J. Org. Chem. 86 (2021) 5690–5701. doi: 10.1021/acs.joc.1c00201

  44. [44]

      M. Zhao, F. Ren, Y. Zhou, Chem. Eur. J. 30 (2024) e202401784. doi: 10.1002/chem.202401784

  45. [45]

      K. Yamamoto, S. Matsui, S.I. Kato, Y. Nakamura, Org. Biomol. Chem. 21 (2023) 5398–5405. doi: 10.1039/d3ob00795b

  46. [46]

      R.Z. Ma, Q.C. Yao, X. Yang, M. Xia, J. Fluorine Chem. 137 (2012) 93–98. doi: 10.1016/j.jfluchem.2012.03.006

  47. [47]

      L. Gai, J. Mack, H. Lu, et al., Chem. Eur. J. 20 (2013) 1091–1102.

  48. [48]

      H. Liu, H. Lu, J. Xu, et al., Chem. Commun. 50 (2014) 1074–1076. doi: 10.1039/C3CC48316A

  49. [49]

      H. Lu, J. Mack, Y. Yang, Z. Shen, Chem. Soc. Rev. 43 (2014) 4778–4823. doi: 10.1039/C4CS00030G

  50. [50]

      J.L. Bredas, Chem. Mater. 29 (2017) 477–478. doi: 10.1021/acs.chemmater.6b04947

• 

  Figure 1  (a) Chemical structures and schematic diagrams of radiation transitions for azulene and 1-azaazulene. (b) Frontier molecular orbitals and their energetics of azulene and 1-azaazulene. (c) Chemical structures, emission peaks, and photoluminescence quantum yields of the 1-azaazulene-based BF₂ complex.

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  Scheme 1  Synthesis route for Ph-NN, Ph-ON, Ca-NN, and Py-NN. (ⅰ) Pd(PPh₃)₄, K₂CO₃, THF, H₂O, 80–110 ℃; (ⅱ) C₄H₉Br, n-BuLi, THF, −78~35 ℃; (ⅲ) BF₃·Et₂O, EtN₃/DIPEA, toluene, 35–80 ℃.

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  Figure 2  Crystal structures and packing diagrams of (a) Ph-NN, (b) Ph-ON, (c) Ca-NN, and (d) Py-NN.

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  Figure 3  (a) UV–vis absorption and (b) emission of compounds Ph-NN, Ph-ON, Ca-NN, and Py-NN (10⁻⁵ mol/L in oxygen-free toluene) with pictures inserted.

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  Figure 4  Frontier molecular orbitals, and their energetics of compounds Ph-NN, Ph-ON, Ca-NN, and Py-NN, obtained by DFT and TD-DFT calculations.

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  Figure 5  (a) OLED device architecture. (b) Electroluminescent emission spectrum at 6 V. (c) The J–V–L (current density–voltage–luminance) characteristics. (d) The EQE–J (external quantum efficiency–current density) relationship.

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  Table 1.  Summarized key photophysical properties of compounds Ph-NN, Ph-ON, Ca-NN, and Py-NN.

  Comp.	λabs (nm)a	λem (nm)a	ΦPL (%)a	τ (ns)a	kr (107 s−1)b	knr (109 s−1)c
  Ph-NN	597	705	0.3	0.18	1.67	5.54
  Ph-ON	487	552	2.9	0.84	3.45	1.16
  Ca-NN	555	653	2.1	0.59	3.56	1.66
  Py-NN	501	560	19.3	2.03	9.51	0.40
  a Meassured in oxygen-free toluene solution (1 × 10−5 mol/L) at room temperature; b Radiative rate constant is calculated as kr =ΦPL/τ; c Non-radiative rate constant is calculated as knr = (1 − ΦPL)/τ.

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