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ABSTRACT Boron-doped acenes have attracted attention due to their unique structures and intriguing luminescent properties. However, the hitherto known boron-doped acenes have only one or two

boron atoms, limiting the chemical space of this unique family of compounds and the capability to tune their optical properties. Herein, we report the synthesis of quadruply boron-doped

acenes, including pentacene, heptacene, and nonacene. The importance of the boron doping level on the luminescent properties of acenes is demonstrated. The title compounds manifest enhanced

Lewis acidity as compared with dihydrodiboraacenes, leading to Lewis-base-responsive emission in the solid state. Moreover, quadruply boron-doped nonacene displays mechanochromic

luminescence in addition to Lewis-base-responsive properties, realizing high-contrast solid-state multicolor emission. This work greatly expands the chemistry of boron-doped acenes and

offers opportunities for developing boron-based luminescent materials. SIMILAR CONTENT BEING VIEWED BY OTHERS AIR- AND PHOTO-STABLE LUMINESCENT CARBODICARBENE-AZABORAACENIUM IONS Article 05

December 2023 AN ELECTROCHEMICALLY RESPONSIVE B–O DYNAMIC BOND TO SWITCH PHOTOLUMINESCENCE OF BORON-NITROGEN-DOPED POLYAROMATICS Article Open access 17 June 2024 EFFICIENT, NARROW-BAND, AND

STABLE ELECTROLUMINESCENCE FROM ORGANOBORON-NITROGEN-CARBONYL EMITTER Article Open access 25 January 2024 INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) consisting of linearly fused

benzene rings, namely acenes (Fig. 1a), have attracted tremendous attention due to their great potential in organic optoelectronics1,2,3,4,5,6,7,8,9,10,11. The introduction of heteroatoms

into the acene backbones toward heteroacenes has proven as a viable strategy for modulating their properties and functions12,13,14,15,16,17. Furthermore, controlling the number of

heteroatoms plays a vital role in precisely manipulating their electronic structures and establishing reliable structure–property relationships18,19,20,21,22,23,24. Among various

heteroatoms, boron possesses a unique vacant p-orbital, thus endowing the π-conjugated system with electron-deficient character25,26,27,28,29,30,31,32,33,34,35,36, Lewis acidity37,38,39,40,

and stimuli-responsive properties41,42,43. Therefore, boron-doped acenes have attracted considerable attention, particularly due to their value as highly luminescent materials44,45,46,47. Up

to now, very few types of boron-doped acenes with only one or two boron atoms have been reported (Fig. 1b, c)48,49,50, whereas those with more than two boron atoms have remained elusive.

Herein, we report the synthesis of quadruply boron-doped acenes (Fig. 1d), including tetrahydrotetraborapentacene (TBP), tetrahydrotetraboraheptacene (TBH), and tetrahydrotetraboranonacenes

(TBN-Hex and TBN-iPr). These boron-doped acenes exhibit stronger Lewis acidity than the previously reported dihydrodiboraacenes, allowing for the modulation of their solid state emission

properties by the formation/disassociation of Lewis acid–base adducts. Moreover, TBN-Hex, with the longest backbone, shows a loose lamella-type packing, which enables further manipulation of

solid state fluorescence by external forces. Variation of the doping level of acenes thus provides a class of tetrahydrotetraboraacenes as multicolor emissive materials. RESULTS SYNTHESIS

AND CHARACTERIZATIONS OF QUADRUPLY BORON-DOPED ACENES The Si/B exchange reaction has been widely used to synthesize different dihydrodiboraacenes via the AA-type homo-annelation of two

bis(trimethylsilyl)-substituted arenes (Fig. 2a)48. In this work, we develop an ABA-type cross-annelation strategy to achieve the synthesis of quadruply boron-doped acenes (Fig. 2b). The

synthetic route is depicted in Fig. 2c. The ABA-type cross-annelation of 1,2,4,5-tetrakis(trimethylsilyl)benzene 1 (one equivalent) and the corresponding bis(trimethylsilyl)-functionalized

arenes 2–5 (two equivalents) in the presence of boron tribromide (BBr3) was carried out to construct the tetrahydrotetraboraacene backbones (6–9). Then, the bulky mesityl (Mes) moieties were

introduced via a nucleophilic substitution, giving TBP, TBH, TBN-Hex, and TBN-iPr in 2.5, 1.7, 13, and 12% yields, respectively. Such relatively low yields were also reported for the

synthesis of dihydrodiboraacenes. Improvements became possible by varying the solvent and reaction time51,52,53. Notably, the AA-type homo-annelation of bis(trimethylsilyl)-functionalized

arenes 2–5 was also observed in this reaction (see Methods), but the multi-boron-doped acenes with six or more boron atoms were not isolated, even by further modulating the ratio of the

precursors. The obtained quadruply boron-doped acenes show good air stability in solutions (Supplementary Fig. 28), and are characterized by 1H and 13C NMR spectroscopies as well as

high-resolution mass spectrometry (HRMS). Single crystals of TBP and TBH suitable for X-ray structural analysis (Fig. 3a, b) were obtained. The growth of high-quality single crystals of

TBN-Hex was difficult, mainly because of the four flexible hexyl chains. Nevertheless, the backbone and the packing structures could be analyzed (Supplementary Fig. 25). In this regard,

TBN-iPr with shorter alkyl chains was employed for crystal growth and proved successful (Fig. 3c), while TBN-Hex was mainly used for further spectroscopic characterizations due to its higher

solubility in common organic solvents. Both TBP and TBH exhibit a planar π-conjugated framework, whereas TBN-iPr displays a bent geometry. In the C4B2 rings, the C–B bond lengths (1.55–1.56

 Å) are slightly shorter than the known C–B single bonds in triphenylborane (1.57–1.59 Å)54, and the C=C bond lengths (1.42–1.45 Å) are longer than the common aromatic C=C bonds (1.41–1.42 

Å), demonstrating the 4π antiaromatic character (Fig. 3d–f). Further theoretical calculations, including the nucleus-independent chemical shift (NICS) values, the isotropic chemical

shielding surface (ICSS) maps, and the anisotropy of the induced current density (ACID) plots demonstrate the gradually decreased antiaromaticity of the C4B2 rings from quadruply boron-doped

pentacene to heptacene and nonacene, which can be attributed to the increased number of aromatic benzene rings reducing the local antiaromaticity by electron delocalization (Fig. 3g–i and

Supplementary Figs. 47,48)55. TBP exhibits a broad optical absorption peaking at _λ_abs = 387 nm, whereas TBH and TBN-Hex show typical vibronic absorption bands with _λ_abs at 440 and 526 

nm, respectively (Fig. 4a–c). Time-dependent density functional theory (TDDFT) calculations reveal that the S0 → S1 transitions of TBP and TBH are forbidden (oscillator strength _f_ = 

0.0000), while the allowed transitions are S0 → S10 (_f_ = 0.2893) for TBP and S0 → S9 (_f_ = 0.3268) for TBH (Supplementary Tables 5–7). By contrast, TBN-Hex shows an allowed S0 → S1

transition with a high oscillator strength of 0.6560, which is in accordance with the large molar extinction coefficient (_ε_) of 51750 M−1 cm−1 (Supplementary Table 4). The emission maxima

(_λ_em) of TBP, TBH, and TBN-Hex are at 512, 466, and 559 nm, and the absolute fluorescence quantum yields (_Φ_F) of these three compounds are determined as 2, 6, and 90%, respectively.

Theoretical calculations of the S1 excited states show that the S1 → S0 transitions of TBP and TBH are forbidden (_f_ = 0.0000), whereas quadruply boron-doped nonacene exhibits an allowed S1

 → S0 transition with a large oscillator strength of 0.7386, which is responsible for its high _Φ_F (Supplementary Tables 8–10). The electrochemical properties of TBP, TBH, and TBN-Hex were

characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements in tetrahydrofuran (Fig. 4d and Supplementary Fig. 27). All compounds exhibit two reversible

reduction waves, with the first half-wave potentials (_E_1/2red) at −1.38 V for TBP, −1.51 V for TBH, and −1.57 V for TBN-Hex, indicating that these tetrahydrotetraboraacenes have higher

electron affinities than their corresponding dihydrodiboraacenes with the first _E_1/2red values ranging from −2.03 to −2.05 V (Supplementary Table 4). According to the DPV data, the lowest

unoccupied molecular orbital (LUMO) energies of TBP, TBH, and TBN-Hex are determined as −3.43, −3.30, and −3.23 eV, respectively, which are lower than those of dihydrodiboraacenes with the

same backbone lengths (−2.72 to −2.78 eV). The Lewis acidity of boron suggested us to investigate the binding constants of quadruply boron-doped acenes with a Lewis base (pyridine).

Titration experiments were performed by monitoring the UV-vis absorption spectra in toluene solutions (Supplementary Fig. 29). Upon adding pyridine from 0 to 2.0 × 10−3 M, the low-energy

absorption bands of TBP, TBH, and TBN-Hex gradually decrease, showing isosbestic points at 370, 401, and 486 nm, respectively. By contrast, the absorption spectra of dihydrodiboraacenes

remain almost unchanged even upon addition of excess pyridine, demonstrating that increasing the number of boron centers boosts the Lewis acidity of boraacenes (Supplementary Fig. 34). To

investigate the upper limit of pyridine coordination with the quadruply boron-doped acenes, we have measured the absorption and fluorescence spectra in pure pyridine, which show different

changes compared with the titration results in toluene solutions. Further single-crystal X-ray analysis confirms a 1:2 coordination mode (one boraacene coordinated with two pyridine

molecules) for TBP with pyridine (Supplementary Fig. 32). Two pyridine molecules coordinate to the boron atoms in a _meta_-_anti_ mode (Supplementary Fig. 33). This experimental observation

is in accordance with DFT calculations, which reveal that the _meta-anti_ coordination mode has the lowest energy among all the possible 1:2 coordinated complexes (Supplementary Table 11).

Moreover, the titration experiment of the quadruply boron-doped acenes with a stronger pyridine base 4-dimethylaminopyridine (DMAP) in toluene solutions was performed (Supplementary Fig. 

35). As increasing the concentration of DMAP, the absorption spectra of the three compounds exhibit similar changes to the pyridine titration results, with the absorption isosbestic points

at 372 nm for TBP, 401 nm for TBH, and 486 nm for TBN-Hex. Further adding DMAP leads to new absorption and emission maxima, with new absorption isosbestic points at 350 nm for TBP, 361 nm

for TBH, and 371 nm for TBN-Hex. The absorption curves match well with those in the pyridine solution, indicating the formation of 1:2 complexes (Supplementary Fig. 36). Therefore, the first

isosbestic points in the initial titration process suggest the formation of 1:1 complexes. The similar absorption changes in the pyridine titration process to the initial DMAP titration

results indicate that these quadruply boron-doped acenes can only form 1:1 complexes with pyridine in toluene solutions. Based on these results, the binding constants _K_ for the three

quadruply boron-doped acenes with pyridine and the two-step binding constants _K_1 and _K_2 with DMAP are calculated and summarized in Supplementary Table 12. For the DMAP complexes, the

ratio of 4_K_2/_K_1 (that is, the _α_ value) is smaller than one, demonstrating that the formation of 1:1 complexes is favorable over 1:2 complexes56. Therefore, stepwise coordination is

observed in toluene. Differently, for the pyridine complexes, the small _K_ values (884 ± 31 M−1 for TBP, 687 ± 16 M−1 for TBH, and 146 ± 3 M−1 for TBN-Hex) of the quadruply boron-doped

acenes with pyridine determine that only the 1:1 complexes are observed in toluene, while the 1:2 complexes can be achieved with pyridine as the solvent. The gradually decreased _K_ values

from TBP to TBH and TBN-Hex are attributed to the enhanced electron-donating effect of the terminal groups (from benzene to naphthene and anthracene), which decrease the Lewis acidity of the

boron atoms. These results are in accordance with the gradually increased LUMO energies and the decreased antiaromaticity of the C4B2 rings57. STIMULI-RESPONSIVE MULTICOLOR EMISSION OF

QUADRUPLY BORON-DOPED ACENES The emission of boron-containing chromophores can be finely adjusted by dynamic coordination of boron with Lewis bases, which makes them promising candidates as

stimuli-responsive materials41. Nevertheless, this behavior has rarely been investigated in the solid state. Exposing the solids of tetrahydrotetraboraacenes to pyridine vapors results in

the changes of _λ_em from 489 to 508 nm for TBP, from 519 to 504 nm for TBH, and from 576 to 514 nm for TBN-Hex (Fig. 5a–c). Obviously, TBP and TBH exhibit small emission wavelength changes,

while TBN-Hex shows a pronounced blue-shifted emission maximum. The corresponding Commission International de l’Eclairage (CIE) coordinates change from (0.26, 0.47) to (0.22, 0.50) for TBP,

from (0.33, 0.54) to (0.21, 0.48) for TBH, and from (0.52, 0.48) to (0.31, 0.59) for TBN-Hex (Supplementary Fig. 40). Moreover, the emission colors can be restored by annealing the exposed

solids at 80 °C for three hours. To shed light on the coordination mode in the solid state, the emission spectra of the pyridine-fumed TBP sample and the single crystal of TBP•2pyridine

complex are compared (Supplementary Fig. 41). The difference in the emission spectra excludes the possibility of forming the 1:2 complex. In addition, the pyridine-fumed TBP sample shows

negligible emission changes compared with the pristine TBP sample. Such a phenomenon is consistent with the titration result of TBP in toluene solutions in the 1:1 coordinated state with

pyridine bases, indicating that only a 1:1 complex of TBP with pyridine is formed in the solid state. Because the binding constants with pyridine is decreasing from TBP to TBH and TBN-Hex,

it is reasonable to conclude that only the 1:1 complexes can be formed upon pyridine fuming in the solid state for all the three compounds. Furthermore, the different emission spectra of

TBN-Hex in the pristine and the fumed states indicate that the pyridine-fumed quadruply boron-doped boraacenes are completely converted to the 1:1 complexes. Upon grinding the TBN-Hex

powder, the emission color dramatically changed from yellow (_λ_em = 576 nm) to red (_λ_em = 605 nm) (Fig. 6a, b). Further fuming the ground TBN-Hex solid with dichloromethane led to an

emissive solid with _λ_em at 583 nm. By contrast, grinding TBP and TBH powders did not substantially alter the emission colors (Supplementary Fig. 43). Powder X-ray diffraction (PXRD) was

performed to give more insights into the mechanochromic luminescence process (Fig. 6c). The pristine TBN-Hex solid exhibits an intense first-order diffraction peak at 6.0° and several weak

peaks at around 10°–25°, indicating an ordered packing structure with a _d_-spacing of 7.4 Å. Upon grinding the solid in a mortar, all diffraction peaks disappear, revealing the amorphous

nature. Interestingly, a diffraction peak at 4.2° (corresponding to a _d_-spacing of 10.5 Å) is observed in the dichloromethane-treated TBN-Hex solid, indicating the formation of a new

crystalline phase different from the pristine solid. Such stimuli-responsive properties are related to the loose lamella-type packing structures (Supplementary Fig. 25)58,59. TBN-Hex

represents an unusual boron-doped chromophore showing both mechanochromic luminescence and Lewis-base-responsive emission in one compound, which makes it a molecular system for increasing

the magnitude of stimuli-responsive fluorescence changes in the solid state. Notably, TBN-Hex solid exhibits remarkable fluorescence change (_λ_em from 514 to 605 nm) and high color contrast

(from green to red in the CIE coordinate diagram) (Fig. 7a, b). The large _λ_em shift (∆_λ_em = 91 nm) of the TBN-Hex solid represents a record for stimuli-responsive boron-doped PAHs

(∆_λ_em < 80 nm)60,61. The utilization of a single compound TBN-Hex to draw a painting with multiple emission colors is thus demonstrated (Fig. 7c), highlighting the potential of

quadruply boron-doped acenes as responsive luminescent materials. DISCUSSION In summary, we have achieved the synthesis of quadruply boron-doped acenes, including pentacene, heptacene, and

nonacene, realizing the highest doping level of boron in acenes. Compared with the previously reported dihydrodiboraacenes, these tetrahydrotetraboraacenes with a higher number of boron

centers exhibit higher Lewis acidity, resulting in stimuli-responsive emissions in the solid state. Moreover, the nonacene homolog shows mechanochromic luminescence properties due to its

loose lamellar packing, leading to high-contrast multicolor emission with the largest _λ_em shift (91 nm) among all boron-doped PAHs. The work thus represents a step forward in the

development of boron-doped acenes and opens up an avenue to exploit heteroacenes as smart luminescent materials in the future. METHODS SYNTHESIS OF TBP To a solution of 2 (602 mg, 2.71 mmol)

and 1 (497 mg, 1.35 mmol) in _n_-heptane (2 mL) was added BBr3 (1.0 mL, 10.8 mmol) at room temperature under an argon atmosphere. The solution was stirred at 120 °C in a sealed tube for 48 

h. After cooling down to room temperature, the mixture was filtrated and the resulting residue was washed with dry hexane for three times and used for the next step directly without further

purification. The obtained solid (125 mg, 0.212 mmol) was suspended in toluene (2 mL) at 0 °C under an argon atmosphere. MesMgBr (1.7 mL, 1.70 mmol, 1.0 M in THF) was slowly added, and the

solution was stirred at room temperature for 18 h. Then, the reaction was quenched with aqueous NH4Cl (5 mL), and the mixture was extracted with dichloromethane three times. The combined

organic layers were dried over anhydrous MgSO4. After removal of the solvents under reduced pressure, the residue was purified via column chromatography over neutral Al2O3 (eluent: PE/DCM = 

1: 0 to 10: 1, _V/V_), giving TBP as a yellow solid (25 mg, 2.5%) and dihydrodiboraanthracene (DBA, see Supplementary Fig. 1) as a white solid (90 mg, 16%). TBP: 1H NMR (400 MHz, CD2Cl2, 298

 K, ppm) _δ_ 7.65–7.58 (m, 6H; Ar-_H_), 7.47 (dd, _J_H,H = 5.6 and 3.6 Hz, 4H; Ar-_H_), 6.77 (s, 8H; Ar-_H_), 2.35 (s, 12H; C_H_3), 1.91 (s, 24H; C_H_3). 13C NMR (400 MHz, CD2Cl2, 298 K,

ppm) _δ_ 149.4, 148.2, 145.7, 140.4, 139.4, 137.8, 137.1, 133.9, 127.0, 22.7, 21.3. The 11B NMR spectrum was not obtained due to the low solubility. HRMS (MALDI) _m/z_: Calcd. for

C54H54B4Na: 769.4495; Found: 769.4511 [M + Na]+. DBA: The characterization data were in accordance with those in the literature62. SYNTHESIS OF TBH To a solution of 3 (816 mg, 2.99 mmol) and

1 (550 mg, 1.50 mmol) in _n_-heptane (5 mL) was added BBr3 (1.2 mL, 12.0 mmol) at room temperature under an argon atmosphere. The solution was stirred at 120 °C in a sealed tube for 48 h.

After cooling down to room temperature, the mixture was filtrated and the resulting residue was washed with dry hexane for three times and used for the next step directly without further

purification. The obtained solid (630 mg, 0.914 mmol) was suspended in toluene (8 mL) at 0 °C under an argon atmosphere. MesMgBr (4.6 mL, 4.60 mmol, 1.0 M in THF) was slowly added, and the

solution was stirred at room temperature for 18 h. Then the reaction was quenched with aqueous NH4Cl (15 mL), and the mixture was extracted with dichloromethane for three times. The combined

organic layers were dried over anhydrous MgSO4. After removal of the solvents under reduced pressure, the residue was purified via column chromatography over neutral Al2O3 (eluent: PE/DCM =

 1: 0 to 5: 1, _V/V_), giving TBH as a yellow solid (22 mg, 1.7%) and dihydrodiborapentacene (DBP, see Supplementary Fig. 1) as a yellowish solid (190 mg, 25%). TBH: 1H NMR (400 MHz, CD2Cl2,

298 K, ppm) _δ_ 8.20 (s, 4H; Ar-_H_), 7.82 (dd, _J_H,H = 6.4 and 3.6 Hz, 4H; Ar-_H_), 7.72 (s, 2H; Ar-_H_), 7.53 (dd, _J_H,H = 6.4 and 3.2 Hz, 4H; Ar-_H_), 6.81 (s, 8H; Ar-_H_), 2.40 (s,

12H; C_H_3), 1.95 (s, 24H; C_H_3). 13C NMR (400 MHz, CD2Cl2, 298 K, ppm) _δ_ 150.2, 148.6, 142.1, 141.5, 140.7, 138.1, 137.0, 136.3, 130.1, 128.9, 127.0, 22.8, 21.4. The 11B NMR spectrum was

not obtained due to the low solubility. HRMS (MALDI) _m/z_: Calcd. for C62H58B4Na: 869.4808; Found: 869.4817 [M + Na]+. DBP: The characterization data were in accordance with those in the

literature53. SYNTHESIS OF TBN-HEX To a solution of 4 (500 mg, 0.777 mmol) and 1 (143 mg, 0.390 mmol) in _n_-heptane (1 mL) was added BBr3 (3.1 mL, 3.10 mmol, 1.0 M in _n_-heptane) at room

temperature under an argon atmosphere. The solution was stirred at 120 °C in a sealed tube for 48 h. After cooling down to room temperature, the mixture was filtrated and the resulting

residue was washed with dry hexane for three times and used for the next step directly without further purification. The obtained solid (238 mg, 0.166 mmol) was suspended in toluene (5 mL)

at 0 °C under an argon atmosphere. MesMgBr (0.8 mL, 0.800 mmol, 1.0 M in THF) was slowly added, and the solution was stirred at room temperature for 18 h. Then the reaction was quenched with

aqueous NH4Cl (6 mL), and the mixture was extracted with dichloromethane for three times. The combined organic layers were dried over anhydrous MgSO4. After removal of the solvents under

reduced pressure, the residue was purified via column chromatography over neutral Al2O3 (eluent: PE/DCM = 10: 1 to 5: 1, _V/V_), giving TBN-Hex as an orange solid (78 mg, 13%) and

dihydrodiboraheptacene (DBH-Hex, see Supplementary Fig. 1) as a green solid (125 mg, 26%). TBN-Hex: 1H NMR (400 MHz, CD2Cl2, 298 K, ppm) _δ_ 7.99 (s, 4H; Ar-_H_), 7.89 (s, 2H; Ar-_H_), 7.77

(dd, _J_H,H = 6.4 and 3.2 Hz, 4H; Ar-_H_), 7.35 (dd, _J_H,H = 7.2 and 3.2 Hz, 4H; Ar-_H_), 7.25 (d, 3_J_H,H = 8.0 Hz, 8H; Ar-_H_), 7.19 (d, 3_J_H,H = 7.6 Hz, 8H; Ar-_H_), 6.64 (s, 8H;

Ar-_H_), 2.72 (t, 3_J_H,H = 8.0 Hz, 8H; C_H_2) 2.30 (s, 12H; C_H_3), 1.86 (s, 24H; C_H_3), 1.76-1.67 (m, 8H; C_H_2), 1.50–1.38 (m, 24H; C_H_2), 0.98 (m, 12H; C_H_3). 13C NMR (400 MHz,

CD2Cl2, 298 K, ppm) _δ_ 150.8, 148.6, 142.8, 142.6, 140.5, 139.8, 137.9, 136.6, 135.1, 132.0, 131.6, 131.4, 128.4, 128.3, 127.9, 126.7, 126.5, 36.2, 32.2, 32.1, 29.8, 23.2, 22.9, 21.4, 14.4.

The 11B NMR spectrum was not obtained due to the low solubility. HRMS (MALDI) _m/z_: Calcd. for C118H126B4: 1587.0232; Found: 1587.0288 [M]+. DBH-Hex: 1H NMR (400 MHz, CD2Cl2, 298 K, ppm)

_δ_ 8.10 (s, 4H; Ar-_H_), 7.80 (dd, _J_H,H = 6.8 and 3.2 Hz, 4H; Ar-_H_), 7.35 (dd, _J_H,H = 6.8 and 2.8 Hz, 4H; Ar-_H_), 7.25 (d, 3_J_H,H = 8.0 Hz, 8H; Ar-_H_), 7.22 (d, 3_J_H,H = 8.0 Hz,

8H; Ar-_H_), 6.66 (s, 4H; Ar-_H_), 2.71 (t, 3_J_H,H = 7.6 Hz, 8H; C_H_2), 2.31 (s, 6H; C_H_3), 1.91 (s, 12H; C_H_3), 1.72 (m, 8H; C_H_2), 1.51–1.40 (m, 24H; C_H_2), 0.99 (m, 12H; C_H_3).

HRMS (MALDI) _m/z_: Calcd. for C94H102B2: 1252.8168; Found: 1252.8203 [M]+. SYNTHESIS OF TBN-IPR To a solution of 5 (404 mg, 0.628 mmol) and 1 (115 mg, 0.313 mmol) in _n_-heptane (1 mL) was

added BBr3 (2.6 mL, 2.60 mmol, 1.0 M in _n_-heptane) at room temperature under an argon atmosphere. The solution was stirred at 120 °C in a sealed tube for 48 h. After cooling down to room

temperature, the mixture was filtrated and the resulting residue was washed with dry hexane for three times and used for the next step directly without further purification. The obtained

solid (110 mg, 0.0769 mmol) was suspended in toluene (2 mL) at 0 °C under an argon. MesMgBr (0.4 mL, 0.400 mmol, 1.0 M in THF) was slowly added, and the solution was stirred at room

temperature for 18 h. Then the reaction was quenched with aqueous NH4Cl (3 mL), and the mixture was extracted with dichloromethane for three times. The combined organic layers were dried

over anhydrous MgSO4. After removal of the solvents under reduced pressure, the residue was purified via column chromatography over neutral Al2O3 (eluent: PE/DCM = 20: 1 to 10: 1, _V/V_),

giving TBN-iPr as an orange solid (57 mg, 12%) and dihydrodiboraheptacene (DBH-iPr, see Supplementary Fig. 1) as a green solid (24 mg, 6%). TBN-iPr: 1H NMR (400 MHz, CD2Cl2, 298 K, ppm) _δ_

7.90 (s, 4H; Ar-_H_), 7.82 (s, 2H; Ar-_H_), 7.69 (dd, _J_H,H = 6.8 and 3.2 Hz, 4H; Ar-_H_), 7.34 (dd, _J_H,H = 6.8 and 3.2 Hz, 4H; Ar-_H_), 7.09 (s, 4H; Ar-_H_), 6.92 (d, 3_J_H,H = 1.2 Hz,

8H; Ar-_H_), 6.56 (s, 8H; Ar-_H_), 2.87 (m, 8H; C_H_), 2.27 (s, 12H; C_H_3), 1.79 (s, 24H; C_H_3), 1.21 (t, 3_J_H,H = 6.4 Hz, 48H; C_H_3). 13C NMR (400 MHz, CD2Cl2, 298 K, ppm) _δ_ 149.0,

142.9, 141.4, 138.0, 137.6, 136.4, 131.9, 131.6, 128.1, 126.8, 126.44, 126.37, 124.1, 34.5, 24.2, 24.1, 22.9. The signals of the carbon atoms connected to the boron were not observed due to

the quadrupolar relaxation of the boron atom. The 11B NMR spectrum was not obtained due to the low solubility. HRMS (MALDI) _m/z_: Calcd. for C118H126B4: 1587.0232; Found: 1587.0298 [M]+.

DBH-iPr: 1H NMR (400 MHz, CD2Cl2, 298 K, ppm) _δ_ 7.97 (s, 4H; Ar-_H_), 7.71 (dd, _J_H,H = 6.4 and 3.2 Hz, 4H; Ar-_H_), 7.34 (dd, _J_H,H = 6.8 and 3.2 Hz, 4H; Ar-_H_), 7.09 (s, 4H; Ar-_H_),

6.93 (d, 3_J_H,H = 1.2 Hz; 8H; Ar-_H_), 6.52 (s, 4H; Ar-_H_), 2.88 (m, 8H; C_H_), 2.27 (s, 6H; C_H_3), 1.80 (s, 12H; C_H_3), 1.22 (m, 48H; C_H_3). HRMS (MALDI) _m/z_: Calcd. for C94H102B2:

1252.8168; Found: 1252.8196 [M]+ SPECTROSCOPY ANALYSIS Absorption spectra were recorded on an Analytikjena Specord 210 Plus UV-vis spectrophotometer. Photoluminescence spectra were recorded

on an Edinburgh FS5 Spectrofluorometer. The photoluminescence quantum yield (PLQY) was measured by using an integrating sphere. The electrochemical measurements were carried out in anhydrous

THF containing 0.1 M _n_-Bu4NPF6 as supporting electrolyte (scan rate: 100 mV s–1) under an argon atmosphere on a CHI 620E electrochemical analyzer. A three-electrode system with glassy

carbon as the working electrode, Ag/AgCl as the reference electrode, and platinum wire as the counter electrode was applied. The potential was calibrated against the ferrocene/ferrocenium

couple. DATA AVAILABILITY The X-ray crystallographic coordinates for structures reported in this study have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under

deposition numbers 2284558 (TBP), 2220546 (TBH), 2259158 (TBN-Hex), 2220548 (TBN-iPr), and 2331286 (TBP•2pyridine). These data can be obtained free of charge from The Cambridge

Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Synthetic procedures and data, experimental details, photophysical and electrochemical characterizations, and

theoretical calculations are provided in the Supplementary Information. Additional data that support the findings of this study are available from the corresponding author upon request. 

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and optoelectronic properties of 9,10-diarylanthracenes. _Dalton Trans_. 42, 13826–13837 (2013). Download references ACKNOWLEDGEMENTS We are grateful to the financial support from the

National Natural Science Foundation of China (Nos. 22071120, 92256304, and 22221002 to X.-Y.W.), the National Key R&D Program of China (2020YFA0711500 to X.-Y.W.), the Beijing National

Laboratory for Molecular Sciences (BNLMS2023013 to X.-Y.W.), and the Fundamental Research Funds for the Central Universities (to X.-Y.W.). The authors cordially thank Dr. Haibin Song and Mr.

Hua Rong (College of Chemistry, Nankai University), as well as Dr. Dieter Schollmeyer (Department of Chemistry, Johannes Gutenberg University Mainz) for single-crystal X-ray structural

analysis. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * State Key Laboratory of Elemento-Organic Chemistry, Frontiers Science Center for New Organic Matter, College of Chemistry, Nankai

University, 300071, Tianjin, China Cheng Chen, Yongkang Guo, Zhidong Chang & Xiao-Ye Wang * Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany Klaus Müllen

* Beijing National Laboratory for Molecular Sciences, Beijing, 100190, China Xiao-Ye Wang Authors * Cheng Chen View author publications You can also search for this author inPubMed Google

Scholar * Yongkang Guo View author publications You can also search for this author inPubMed Google Scholar * Zhidong Chang View author publications You can also search for this author

inPubMed Google Scholar * Klaus Müllen View author publications You can also search for this author inPubMed Google Scholar * Xiao-Ye Wang View author publications You can also search for

this author inPubMed Google Scholar CONTRIBUTIONS X.-Y.W. conceived the project. C.C., Y.G., and Z.C. synthesized the compounds and conducted all characterizations and theoretical studies

under the supervision of X.-Y.W. C.C., K.M., and X.-Y.W. analyzed the data and wrote the manuscript. All authors commented on it. CORRESPONDING AUTHOR Correspondence to Xiao-Ye Wang. ETHICS

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