Independently Tuned Frontier Orbital Energy Levels of 1,3,4,6,9b

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Independently Tuned Frontier Orbital Energy Levels of 1,3,4,6,9b-Pentaazaphenalene Derivatives by Conjugation Effect Hiroyuki Watanabe, Kazuo Tanaka, and Yoshiki Chujo J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b03161 • Publication Date (Web): 30 Jan 2019 Downloaded from http://pubs.acs.org on February 4, 2019

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The Journal of Organic Chemistry

Independently Tuned Frontier Orbital Energy Levels of 1,3,4,6,9b-Pentaazaphenalene Derivatives by Conjugation Effect Hiroyuki Watanabe, Kazuo Tanaka*, and Yoshiki Chujo

Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan E-mail: [email protected]

Key words: Azaphenalene; heterocycle; HOMO-LUMO gap; absorption

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ABSTRACT Herein reported is syntheses and unique substituent effect in 1,3,4,6,9b-pentaazaphenalene (5AP) derivatives. We developed the new synthetic route via (N,N-pyridine-2,6-diyl)bisamides, which enabled us to prepare a variety of substituted 5APs and to systematically investigate the substituent effects on the electronic structures of the multi-N-heterocyclic 5APs using UV–vis absorption spectroscopy, cyclic voltammetry and density functional theory calculations. From the analyses, we found that the substituent effects regarding the electronic states of 5APs drastically varied depending on the substitution position. It was revealed that the conjugation effects from the substituents were specifically expressed either highest occupied molecular orbitals (HOMOs) or lowest unoccupied molecular orbitals (LUMOs) by altering the substitution position at the 5AP ring. As a result, small HOMO–LUMO gap were accomplished only by elevating HOMOs or by lowering LUMOs. Intrinsically separated HOMO and LUMO of 5AP is the origin of this unique substituent effect. These results suggested that HOMOs and LUMOs can be independently tuned by the conjugation effects in 5APs. This selective tunability of an either frontier orbital is a desired character for application of organic molecules as modern optoelectronic devices and advanced organic electronic materials.

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INTRODUCTION Hückel’s [4n+2] rule is a basic concept in organic chemistry, which refers to the aromaticity of monocyclic π-conjugated systems.1 Extension of Hückel’s rule to polycyclic systems has been tried,

and

several

theoretical

models

such

as

the

perimeter

models

and

the

annulene-within-an-annulene (AWA) models2 were proposed. Although there are still much room to be sophisticated in each model for improving applicability3–6 and removing limitations,4–6 it should be stated that macrocyclic π-conjugated systems other than ordinary acenes show high structure-dependency in their unique aromaticity and properties.7,8

Phenalenyl anion, cation and related isoelectronic species are a class of interesting macrocyclic π-conjugated systems. They schematically have a 12π-electron system (“outside” electrons) in the perimeter and the central atom (“inside” electrons, 9-C in the parent phenalenyl) interacts with the perimeter. This situation of phenalenyls, the interaction between the “inside” and “outside” electrons, is similar to that of the AWA model. Fowler and Jenneskens et al. called the phenalenyl structure as “a magnetic chameleon”, referring to the interesting behavior of their aromaticity depending on the central atom.9 In terms of the magnetic properties (ring current, nucleus-independent chemical shift (NICS), and magnetic susceptibility), phenalenyl cation and anion show aromaticity, whereas 9b-boraphenalene and 9b-azaphenalene (isoelectronic to phenalenyl cation and anion, respectively) show antiaromaticity. On the other hand, in terms of energetic properties (aromatic stabilization energies (ASE)), all four species had positive ASE values (indicated their aromaticity). 3



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In the course of our research on “element-blocks” (functional building blocks containing heteroatoms),10,11 we have reported the introduction of novel π-conjugated building blocks to the π-conjugated systems and their intriguing optical and electronic properties originating from each element-block. Their unique performances of the element-block were also successfully reflected in the π-conjugated systems.12,13 Therefore such an interesting behavior of phenalenyl and its isoelectronic species motivated us to explore their properties as a building block of π-conjugated system.

As

one

of

promising

conjugated

element-blocks,

we

have

focused

on

1,3,4,6,9b-pentaazaphenalene (Figure 1, 5AP) and its derivatives including π-conjugated polymers.14–16 5AP has an isoelectronic structure of phenalenyl anion (PA) and substitution of five carbon atoms to nitrogen atoms leads to the neutral and stable 5AP scaffold.17,18 PA and its isoelectronic species including 5AP can be classified as non-benzenoid aromatic compounds (NBAs) because they show energetic stabilization by π-conjugation which indicates its aromaticity19,20 and their fourteen π-electrons delocalized over the triangle structure without localization into any six-membered ring. After the first synthesis of 9b-azaphenalene by Farquhar and Leaver,21 in the 1970s to 1980s, syntheses of azaphenalene (AP) derivatives were achieved.18,22–24 The stability of AP derivatives were, especially in detail, theoretically discussed17 and experimentally analyzed18,24 based on the theory of topological charge stabilization.17 On the other hand, the properties of APs as building blocks for π-conjugated 4


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organic materials were hardly investigated. One of the main reasons may be the limited synthetic route toward AP derivatives.

7

9

5

2

Figure 1. Structures of PA and azaphenalenes. The number of substituent positions is shown for 5AP.

In this research, we focused on 5AP among APs because of its high stability and functionality to exhibit unique properties originating from the trigonally-fused 12π (peripheral [12]annulene) + 2π (the central nitrogen atom) conjugated system. Although there have been a few reports on partial functionalization with the 5AP rings,22,23,25–29 it is still challenging to apply 5AP-based π-conjugated systems for constructing optoelectronic materials according to preprogrammed designs due to the limited number of chemical modification methods. We initially established a versatile synthetic route for constructing the 5AP structure and subsequently discovered fundamental optical and electrochemical characteristics from the series of 5APs. It was suggested that frontier orbitals were differently affected by the conjugation effect in the case of 2,5-disubstituted 5APs (4a-e) and 7,9-disubstituted 5APs (6a-e). It means the dependency of the 5



substituent effect on the position of the substituent. Theoretical calculation clarified that the origin of the unique substituent effect was the spatially separated frontier orbitals, which originated from the π-conjugated system of 5AP.

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RESULTS AND DISCUSSION Firstly we tried to synthesize 5AP derivatives via the condensation of 2,6-diaminopyridine and methyl N-cyanoimidates (1a and 1b, Scheme 1).23 Although non-substituted 5AP and 2,5-dimethyl 5AP were synthesized in moderate yields in the literature,23 the method was not suitable for our initial target molecules; 2,5-di(tert-butyl) 5AP (2a, 3% isolated yield) and 2,5-di(4-(tert-butyl)phenyl) 5AP (2b, 4% isolated yield). These results clearly indicated that alternative synthetic route should be necessary for obtaining 2,5-disubstituted 5AP derivatives which are expected to provide us with insight into electronically perturbed 5AP derivetives.

Shaw et al. suggested that the formation of 5AP from 2,6-diaminopyridine and N-cyanoimidates is composed of the two steps. The intermolecular condensation of 2,6-diaminopyridine was supposed to be the rate-determining step.23 Based on the assumption that inefficient condensation could result in low reaction yields in the preliminary experiments, we replaced the condensation step to the reaction with 2,6-diaminopyridine and acyl chlorides (Scheme 2). The resulting amides (Scheme 2, 3a-g) were able to be transformed into the imidoyl chlorides.30 It was presumed that they can be further transformed into the plausible intermediate by Shaw et al. (Scheme 2) after nucleophilic additions by two equivalents of cyanamide. Addition of an excess amount of cyanamide to the imidoyl chloride smoothly afforded 5APs. It should be noted that the plausible intermediate in our reaction was reported to be a precursor for vacuum pyrolysis synthesis of APs.18 Details of our design and plausible mechanism of this efficient and versatile synthetic scheme of 5AP is described in Supporting Information (SI, Section 1). As a consequence, 2a, the synthesis of which was difficult in the conventional 7



scheme, was obtained in 69% isolated yield (Scheme 2). 2a was fully characterized by 1H and 13

C{1H} NMR spectroscopy, high-resolution mass spectroscopy and single-crystal X-ray

structure analysis (Figure 2).31 It is surprising since fused planar π-conjugated molecules are prone to suffer from low solubility, meanwhile 2a was readily soluble in most of common organic solvents even as methanol and hexane. 2b was also obtained by this reaction in 71% isolated yield through our synthetic route.

Figure 2 shows the crystal structure and packing of 2a determined from single-crystal X-ray analysis. The sum of three C-N-C bond angles around the 9b (central) nitrogen atom was 360.01°, which suggested the high planarity of 5AP scaffold. It agreed with the literatures suggesting that the lone pair on 9b nitrogen atom contributes to the entire π-conjugated system24 and does not have basicity32. The packing was face-to-face and anti-parallel. The distance between two faced 2a molecules was 4.03 Å (> sum of van der waals radii of two carbon atoms). The π-π stacking of 2a might have been suppressed by steric hindrance between tert-butyl groups on 2 and 5 positions of 5AP scaffold. The anti-parallel packing probably originated from the polarity of 5AP core.

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Scheme 1. Synthesis of 2,5-substituted 5APs by the conventional scheme

9



a)

b) 122.57°

118.72°118.72°

c)

d)

4.03 Å

Figure 2. ORTEP (a) top, (b) side and (c,d) packing views of 2a obtained by single crystal X-ray structure analysis. Thermal ellipsoid plot is shown at 50% probability level. All hydrogen atoms are omitted for clarity. Details of the analysis is described in the CIF file (CCDC 1535792). Crystallographic data is in Table S27. 10


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Various 2,5-substituted 5APs (Scheme 2) were prepared with the same procedure. A variety of π-conjugated substituents having electron-withdrawing and electron-donating characters were introduced. As Shaw et al.25 and we14–16 have reported, 7 and 9 positions of 5AP can be easily brominated by electrophilic aromatic substitution reaction. A wide range of substituents were able to be introduced by subsequent Suzuki–Miyaura cross coupling reaction. 7,9-Disubstituted 5AP derivatives (Scheme 3) were also synthesized in order to be compared with 4a-e. All 4a-e and 6a-e were characterized by 1H and

13

C{1H} NMR spectroscopy and high-resolution mass

measurements. These 5AP derivatives had good stability enough for evaluating optical and electrochemical analyses to clarify substituent effects of NBAs on different positions and provide general insight into electronic states of NBAs.

Scheme 2. Synthesis of 2,5-substituted 5APs from amide precursors and its plausible mechanism

a

Isolated yields from corresponding amides. bRefluxed for 24 h. cPCl3 was used instead of PCl5. 11



Scheme 3. Synthesis of 7,9-substituted 5APs via Suzuki-Miyaura cross coupling reaction

a

Isolated yields from 5.

Optical properties of 5APs were investigated in chloroform solutions and the spectra of 5APs with the same type of substituents were represented with the same colored line for clarity (Figure 3). The results of UV–vis absorption spectroscopy are summarized in Table 1. Quite different features were obtained in the UV−vis absorption spectra of 2,5-substituted 5APs (4a-e; Figure 3a, c) and 7,9-substituted 5APs (6a-e; Figure 3b, d). In 4a-e, red-shifted spectra were obtained when electron-withdrawing substituents were introduced (i.e. 4a and 4b), whereas red-shifts of the absorption bands of 6a-e were caused by electron-donating substituents (i.e. 6d and 6e). These tendencies mean that the electronic properties of 5APs can be significantly influenced by the position of the substituent. The weak absorption bands in the longer wavelength region were assignable to the symmetry-forbidden HOMO–LUMO transition according to the previous literatures.14,15,24 This assignment was also applicable in this study according to theoretical calculations (See SI). It should be noted that the assignment is changed as the transition between HOMO−2 and LUMO in the case of 4e although the character of the transition (the transition from the HOMO of the 5AP moiety to the LUMO delocalized over the molecule) remained intact. It is merely because the high HOMO energy levels of the 4-diphenylamine substituents is located 12


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over the intrinsic HOMO of the 5AP moiety in 4e. Thereby, the apparent assignment is different from others, similarly to the 5AP-containing conjugated polymer where the LUMO of the 5AP monomer was converted to the LUMO+2 only in the copolymer with benzothiadiazole because of intrinsically-low LUMO energy level of the benzothiadiazole unit.15 These spectra indicated that the substituent of 5AP derivatives differently affected their HOMO–LUMO gaps depending on the substituent position. Because the HOMO–LUMO transition of 5AP is symmetry-forbidden, emission was hardly observed in this study.14,15,24

13



Figure 3. UV–vis absorption spectra of (a) 2a, 4a-e and (b) 6a-e (1.0 × 10−5 M in chloroform). Enlarged spectra in the visible region of (c) 2a, 4a-e and (d) 6a-e (1.0 × 10−4 M in chloroform).

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Table 1. Summary of optical properties 2,5-substituted series 7,9-substituted series a b Substituent Compound short λ long λ Compound short λa long λb λabs εmax λabs εmax λabs εmax λabs εmax [nm] [M−1cm−1] [nm] [M−1cm−1] [nm] [M−1cm−1] [nm] [M−1cm−1] tBu 314 19 200 575 820 – – – – 2a (4-CN)Ph 315 38 900 672 690 379 30 800 607 2 190 4a 6a (4-CF3)Ph 305 41 500 657 870 364 26 400 608 1 630 4b 6b Ph 317 35 700 636 840 353 24 200 615 1 420 4c 6c (4-OMe)Ph 356 54 500 622 1 580 358 27 100 624 1 530 4d 6d # # (4-NR2 )Ph 347 26 200 626 3 320 372 33 300 646 2 000 4e 6e a b From absorption bands in the shorter wavelength region (λ < 400 nm). From weak absorption bands in the longer wavelength region. R = Ph for 4e and R = Me for 6e. ##A strong peak at λabs = 450 nm had the large contribution from the local excitation in the (4-diphenylamino)phenyl moiety, therefore instead we show the similar transition to other 2,5-substituted 5APs in this table. For the details of the assignment, see Supporting Information (Section 6). #

15



Cyclic voltammetry was performed to independently evaluate the HOMO levels (EHOMO,CV) and the LUMO levels (ELUMO,CV) of 5APs using ferrocene/ferrocenium half-wave potential (–5.10 eV) as an external standard (Table S14,15 and Figure S45).33 It should be noted that the relationship between the electrochemical (onset or half-step) potential and the frontier molecular energy levels has been still much debated.33 Here we estimated (not determine) the HOMO or LUMO levels from the onset potential of first oxidation or reduction peaks. The estimated energy levels are summarized as diagrams in Figure 4. Their absolute values have large uncertainties, nevertheless it could be stated that they are useful for comparing the 5APs to evaluate the differences originating from the substituent effects. It was shown that, substituents strongly affected ELUMO,CV and weakly affected EHOMO,CV in 2,5-substituted 5APs (4a-e), while completely-opposite tendency was observed from 7,9-substituted 5APs (6a-e). The optical properties obtained from UV–vis absorption measurements can be rationalized by the electrochemical data. Electron-withdrawing substituents in 4a-e especially lowered ELUMO,CV, which induced the red-shifted spectra. The substituents in 4a-e made a difference of 0.37 eV in LUMOs, which is significantly larger than a difference of 0.26 eV in HOMOs. (Here we omitted 2a because it does not have phenyl spacers and 4e because its HOMO was not from 5AP scaffold but from triphenylamine units.) In contrast, electron-donating substituents in 6a-e upraised EHOMO,CV resulting in red-shifted spectra. The difference due to substituent effects were 0.57 eV in HOMOs and 0.28 eV in LUMOs. It is clearly indicating that only one of the frontier molecular orbitals should be strongly perturbed by the conjugation effect of the substituents. The substituent effect on 5AP was completely different depending on the position.

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Figure 4. Energy levels of HOMOs and LUMOs estimated from cyclic voltammetry measurements. The onset potentials were converted to the electron volt unit according to the following formula: EHOMO (eV) = –5.10-Eox,onset, ELUMO (eV) = –5.10-Ered,onset.33

In our previous report on 5AP-containing π-conjugated polymers, it was found that π-conjugated system can be extended only through HOMO via the 7,9-positions of 5AP.15 It was suggested that LUMOs of each unit were isolated even though they are incorporated and connected in the same polymer main-chains. On the basis of this unique electronic structure, we proposed that 5AP is the conjugated element-block creating the “isolated-LUMO” state in conjugated polymers. The optical and electrochemical data suggest that the isolated-LUMO state is also realized in 6a-e. To realize the “isolated-LUMO” state, it is essential to obtain the spatially 17



separated HOMO and LUMO on the 5AP ring. To confirm the distributions of HOMOs and LUMOs, the theoretical calculations were performed (Figure 5, S45 and S46). Apparently, in the cases of 4a-e and 6a-e, distribution of the lobes of HOMO were different from those of LUMO. In addition, when the substituents are introduced into the 2,5-positions of 5AP, the energy level of LUMO of 5AP was strongly perturbed, whereas that of HOMO was hardly affected in terms of the conjugation effect. Because not HOMO but LUMO exists at these positions, these changes in the substituent effect should be induced. In the case of 7,9-substituted 5APs, the opposite effects were observed because not LUMO but HOMO exists at positions where the substituents were introduced. These unique extension of π-conjugated system either HOMO or LUMO of 5AP might be originated from the anti-aromatic nature of peripheral moiety of 5AP because the HOMO and LUMO of 5AP have the character of the degenerated SOMOs of [12]annulene.24

b)

c)

LUMO

a)

7

9

5

2 HOMO

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Figure 5. Frontier orbitals of (a) 2, (b) 4c and (c) 6c at B3LYP/6-31+G(d,p) level of theory. 18


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To obtain deep insight, quantitative evaluation by density functional theory (DFT) and time-dependent

DFT

(TD-DFT)

method

using

Gaussian

09

D.01

package34

at

B3LYP/6-31+G(d,p) level of theory was executed with experimental and theoretical data. In Figure 6 and Tables S12 and S13, we compare the experimental data and the calculated values. Although they do not absolutely match, the trends were reproduced so well that we are motivated to calculate and analyze the difference originating from the electronic nature of substituents. (As we describe the reason in the section of cyclic voltammetry, 2a and 4e were omitted for clarity.) In the cases of EHOMOs and ELUMOs, we can compare 4a-d and 6a-e to conclude that the substituents of 2,5-subsrtitued 5APs (4a-d) induced the experimental differences of 0.26 eV (HOMO) and 0.37 eV (LUMO). Likewise, from theoretical data, the differences of 0.78 eV (HOMO) and 0.97 eV (LUMO) were proved to be induced by the substituent effects in 2,5-subsrtitued 5APs (4a-d). Both of experimental and simulated differences indicated that the substituent effects were stronger in LUMO than in HOMO. In contrast, the differences were larger in HOMO about 7,9-substitued 5APs (6a-e), as follows: 0.57 eV (HOMO, experimental), 0.28 eV (LUMO, experimental), 1.22 eV (HOMO, theoretical) and 0.86 eV (LUMO, theoretical). These well agreements in the trends of EHOMOs and ELUMOs resulted in the reproduced trend in HOMO–LUMO gaps and optical band gaps (Figures 6c-6f). As we described in this section, the tendency of substituent effects in UV–vis absorption spectra and cyclic voltammetry were qualitatively consistent with the calculation results. Other peaks than HOMO–LUMO transition in UV–vis absorption spectra were able to be assigned based on the results of TD-DFT single point calculations (Tables S1−S11). These agreements of the results from our experiments and calculations strongly support validity of our discussion based on the spatially separated frontier orbitals and resulting unique π-conjugated system of 5APs. We might have to mention about the 19



energies of the localized orbital on 5AP (HOMOs of 4a-d and LUMOs of 6a-e), which differed a little depending on the substituents. We assume that it might derive from the inductive effect of substituent, which does not need the π-conjugation between the substituents and the 5AP scaffold.

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Figure 6. Comparisons of (a,b) orbital energies of HOMOs and LUMOs estimated from CV measurements (EHOMO,CV and ELUMO,CV) and calculated by the DFT method (EHOMO,DFT and ELUMO,DFT), (c,d) Eg,CV (ELUMO,CV − EHOMO,CV) and Eg,DFT (ELUMO,DFT − EHOMO,DFT) and (e,f) Eg,opt (energy of the onset wavelengths in absorption spectra) and ES0−S1,DFT (the vertical excitation energy from the ground state to the excited state 1 calculated by the TD-DFT method).; 21



CONCLUSION In this paper, new synthetic route to 5AP derivatives were developed. Consequently, electronic states of 5APs were widely modulated by the substituents. The unique behaviors of UV–vis absorption spectra, electrochemical measurements and theoretical calculations indicated that the conjugation effects of substituents affected only one of the HOMO or LUMO level depending on the substitution position. As an related example of the substituent effect in 5AP, Plattner pointed out the substitution-position-dependent behavior of the methyl-substituted azulene derivatives.35 Moreover, several groups have implied that it was able to be attributed to the existence of either frontier molecular orbital at the positions.36,37 Katagiri et al. stated that the extension of π-conjugated system in terazulenes (trimer of azulene) depends on the regioregularity.38 Azulene-containing polymers have been reported to have different properties depending on the connectivity between azulene and comonomers.39,40 It is still unclear whether such a behavior is characteristic of NBAs because the number of extensive studies on NBAs are limited. In addition, researches on porphyrin41,42 and pyrene43–46 systems suggested the dependency of substituent effects on substituent positions is of importance in benzenoid π-conjugated system. In the case of azulene derivatives, systematic investigation regarding a series of substituent positions and electronically different substituents has not been achieved due to the limitation of the functionalization method of the azulene scaffold. Therefore, it is no doubtful that there are much room to examine the conjugation effect on NBAs. From this point of view, it could be stated that this work on 5AP affords further electronic insight about NBAs. The advantage of 5AP-based system would be the distance of the substituted positions. 1,3-positions and 2-positions (functionalizations have been reported47,48) of azulene are too close to cooperatively exhibit conjugation effects. These findings suggest that 5AP would be promising building materials 22


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based on novel π-conjugated systems where the HOMOs and the LUMOs are independently affected by conjugation effect by substituents, though the inductive effect from substituents inevitably affect the both HOMOs and LUMOs. Other types of 5APs including tri- and tetrasubstituted ones are currently investigated in our laboratory and will be reported in the near future. They may open the way to full-tuning of the frontier orbital levels in organic materials. In the organic electronic materials, fine-tuning of frontier orbital levels is needed for receiving high efficiency. 5AP derivatives could be a promising building block for realizing such materials through specific tuning of frontier orbital levels with the conjugation effect. The small molar absorption coefficient of 5APs motivates us to apply them for carrier transport materials in organic electronics. Researches toward the application of 5AP as carrier transport materials with tunable HOMO / LUMO energies are now underway in our laboratory.

23



Experimental section

General 1

H (400 MHz) and 13C{1H} (100 MHz) NMR spectra were recorded on JEOL JNM-EX400 or

JNM-AL400 spectrometers. 1H and

13

C{1H} NMR spectra in CDCl3 were recorded by using

tetramethylsilane (TMS) as an internal standard. 1H and

13

C{1H} NMR spectra in CD2Cl2 and

DMSO-d6 were recorded by using residual solvents as internal standards. High-resolution mass spectra (HRMS) were obtained on a Thermo Fisher EXACTIVE Plus Fourier-transform (orbitrap) mass spectrometer for electron spray ionization (ESI). UV–vis absorption spectra were recorded on a Shimadzu UV-3600 spectrophotometer. Cyclic voltammetry (CV) was carried out on a BAS ALS-Electrochemical-Analyzer Model 600D with a glassy carbon working electrode, a Pt counter electrode, an Ag/Ag+ reference electrode, and the ferrocene/ferrocenium external reference at a scan rate of 0.1 Vs‒1. All reactions were performed under argon atmosphere. X-ray crystallographic analysis was carried out by Rigaku R-AXIS RAPID-F graphite-monochromated Mo Kα radiation diffractometer with an imaging plate. The analysis was carried out with direct methods (SHELXT-2014, SHELXL-201449) using Yadokari-XG50. Details of the structure analysis are described in the CIF file (CCDC 1535792). The program Mercury51 was used to generate the X-ray structural image with thermal ellipsoid plots.

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Materials Reagents (pivalaldehyde, sodium tert-butoxide (tBuONa), 4-(tert-butyl)benzaldehyde, 2,6-diaminopyridine,

pivaloyl

chloride,

benzoyl

chloride,

4-methoxybenzoyl

chloride,

4-(trifluoromethyl)benzoyl chloride, 4-cyanobenzoylchloride, 4-diphenylamino(benzaldehyde), potassium permanganate, oxalyl chloride, cyanamide, phosphorus pentachloride (PCl5), N-bromosuccinimide, (2-dicyclohexylphosphino-2’,6’-dimethoxybiphenyl)[2-(2’-amino-1,1’-biphenyl)]palladium(II) methanesulfonate dichloromethane adduct (SPhos Pd G3), benzeneboronic acid pinacol ester, 4-methoxybenzeneboronic acid, 4-(N,N-dimethylamino)benzeneboronic acid pinacol ester, 4-(trifluoromethyl)benzeneboronic acid pinacol ester, 4-cyanobenzeneboronic acid pinacol ester and cesium carbonate) and dry solvents (methanol, N,N-dimethylformamide, dichloromethane and toluene) were purchased from commercial sources and used without further purification. Tetrahydrofuran (THF), diethyl ether (Et2O) and triethylamine (NEt3) were purified using a two-column solid-state purification system (Glasscontour System, Joerg Meyer, Irvine, CA). Glyme (1,2-dimethoxyethane) was degassed by Ar bubbling prior to use. Water for the Suzuki‒Miyaura cross coupling reactions was degassed by Ar bubbling prior to use.

25



Synthetic procedures Syntheses of 5APs via the condensation of 2,6-diaminopyridine and N-cyanomimidates. N-Cyanomidates were synthesized according to the literature procedure.52 • Methyl N-cyanopivalimidate (1a) tBuONa (22.4 g, 200 mmol) was charged in a two-neck round-bottom flask in the glovebox. Dry MeOH (deoxidized) 300 mL was added. To this solution was added pivalaldehyde (5.52 mL, 4.31 g, 50.0 mmol) and cyanamide (8.52 g, 203 mmol). After stirring for 0.5 h, N-bromosuccinimide (36.5 g, 205 mmol) was added. Then the solution was warmed to 50 °C and stirred 18 h. After the solution was cooled to room temperature, the reaction mixture was filtered and the solvents were removed in vacuo. The residual oil was purified by column chromatography on silica gel (eluent: hexane / EtOAc = 10:1 (v/v)) to afford the product as a colorless oil (2.07 g, 14.8 mmol, 30% isolated yield). 1H NMR (CDCl3, ppm): δ 3.84 (s, 3H, OMe), 1.41 (s, 9H, tBu).

C{1H} NMR (CDCl3, ppm): δ 187.4, 112.4, 56.6, 41.5, 28.8. HRMS

13

(ESI-orbitrap) m/z: [M+Na]+ Calcd for C7H12N2ONa 163.0842; Found 163.0839. • Methyl 4-(tert-butyl)-N-cyanobenzimidate (1b) Following the procedure for the synthesis of methyl N-cyanopivalimidate, the product was obtained from 4-(tert-butyl)benzaldehyde after the purification by column chromatography on silica gel (eluent: hexane / EtOAc = 8:1 (v/v)) as a colorless oil (4.02 g, 18.6 mmol, 57% isolated yield). 1H NMR (CDCl3, ppm): δ 8.04 (d, J = 8.8 Hz, 2H, Ar), 7.52 (s, J = 8.8 Hz, 2H, Ar), 4.04 (s, 3H, OMe), 1.34 (s, 9H, tBu).

13

C{1H} NMR (CDCl3, ppm): δ 174.8, 157.7, 128.6, 126.5,

26


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125.8, 113.6, 56.6, 35.2, 31.0. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C13H17N2O 217.1335; Found 217.1334. • 2,5-Di-tert-butyl-1,3,4,6,9b-pentaazaphenalene (2a) A glyme (0.5 mL) solution of 2,6-diaminopyridine (0.151 g, 1.38 mmol) and methyl N-cyanopivalimidate (0.48 g, 3.4 mmol) was stirred at 80 °C for 27 h. After it was allowed to cool to room temperature, the reaction mixture was diluted by CHCl3 and washed by water three times. The organic layer was dried over MgSO4 and then evaporated. After purification by column chromatography on silica gel, 2a was obtained as a red solid (12.1 mg, 0.043 mmol, 3% isolated yield). Characterization data is shown in the following procedure of our synthetic method.

• 2,5-Di-(4-tert-butylphenyl)-1,3,4,6,9b-pentaazaphenalene (2b) A glyme (0.5 mL) solution of 2,6-diaminopyridine (0.412 g, 3.76 mmol) and methyl 4-(tert-butyl)-N-cyanobenzimidate (2.06 g, 9.52 mmol) was stirred at 80 °C for 57 h. After it was allowed to cool to room temperature, the reaction mixture was diluted by CHCl3 and washed by water three times. The organic layer was dried over MgSO4 and then evaporated. After purification by column chromatography on silica gel and recrystallization from CHCl 3 / MeOH (70 °C), 3b was obtained as a purple solid (68.1 mg, 0.156 mmol, 4% isolated yield). Characterization data is shown in the following procedure of our synthetic method. Syntheses of amides (3a-g).

27



Although some of them are reported in the literature,30 our modified experimental procedure and characterization data are described. • N,N’-(Pyridine-2,6-diyl)bis(4-cyanobenzamide) (3a) An ice-cooled CH2Cl2 (50 mL) solution of 2,6-diaminopyridine (2.91 g, 26.7 mmol) and NEt3 (10 mL, 7.6 g, 75 mmol) was stirred. To the solution was added a CH2Cl2 (25 mL) solution of 4-cyanobenzoyl chloride (10 g, 60 mmol) dropwise. After the addition was completed, the reaction mixture was allowed to warm to room temperature and stirred for 22 h. Then the mixture was poured into 200 mL H2O and a colorless precipitate formed. The precipitate was washed by MeOH. The organic layer was washed by brine, dried over MgSO4. After filtration, the solvents were removed in vacuo. The residual solid was washed by hot EtOH (80 °C) and CH2Cl2. 3a was obtained as a colorless solid (9.20 g, 25.1 mmol, 94% isolated yield). 1H NMR (DMSO-d6, ppm): δ 10.82 (br s, 2H, NH), 8.11 (d, J = 8.5 Hz, 4H, Ph), 7.98 (d, J = 8.5 Hz, 4H, Ph), 7.87 (m, 3H, Py).

13

C{1H} NMR (DMSO-d6, ppm): δ 164.6, 150.1, 140.0, 138.1, 132.3, 128.6, 118.1, 114.1,

111.6. HRMS (ESI-orbitrap) m/z: [M–H]– Calcd for C21H12N5O2 366.0996; Found 366.0999.

• N,N’-(Pyridine-2,6-diyl)bis(4-(trifluoromethyl)benzamide) (3b) An ice-cooled CH2Cl2 (150 mL) solution of 2,6-diaminopyridine (6.52 g, 59.7 mmol) and NEt3 (17 mL, 12 g, 120 mmol) was stirred. To the solution was added a CH2Cl2 (50 mL) solution of 4-(trifluoromethyl)benzoyl chloride (24.7 g, 118 mmol) dropwise. After the addition was completed, the reaction mixture was allowed to warm to room temperature and stirred for 21 h. Precipitates formed and were collected by filtration. Hot filtration of the precipitate from EtOH 28


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(80 °C) afforded 3b as colorless solid (24.2 g, 53.4 mmol, 89% isolated yield) after washing by CH2Cl2 and EtOH. 1H NMR (DMSO-d6, ppm): δ 10.80 (br s, 2H, NH), 8.17 (d, J = 8.2 Hz, 4H, Ph), 7.88–7.95 (m containing d (J = 8.2 Hz), 7H, Ph and Py). 13C{1H} NMR (DMSO-d6, ppm): δ 164.9, 150.2, 140.7, 137.9, 131.5 (q, J = 32 Hz), 128.8, 123.0 (q, J = 272 Hz), 125.2 (br), 111.7. HRMS (ESI-orbitrap) [M–H]– Calcd for C21H12F6N3O2 452.0839; Found 452.0837. • N,N’-(Pyridine-2,6-diyl)dibenzamide (3c) To an ice-cooled THF (50 mL) solution of 2,6-diaminopyridine (5.28 g, 48.4 mmol) and NEt3 (18 mL, 13 g, 130 mmol) was added a THF (30 mL) solution of benzoyl chloride (13 mL, 16 g, 110 mmol) dropwise. After the addition was completed, the reaction mixture was allowed to warm to room temperature and stirred for 20 h. Precipitates formed and were removed by filtration and washed by THF (5 × 10 mL). The solvents were removed from the filtrate and the yellow solid was obtained. The residual solid was washed by hexane / EtOAc (80 °C) then EtOH (80 °C). After filtration, 3c was obtained as a colorless solid (11.8 g, 37.1 mmol, 77% isolated yield). 1H NMR (DMSO-d6, ppm): δ 10.65 (br s, 2H, NH), 8.01 (m, 4H, Ph), 7.93 (m, 1H, Py), 7.85 (m, 2H, Py), 7.61 (tt, J = 1.0 Hz, 7.3 Hz, 2H, Ph), 7.53 (t, J = 7.3 Hz, 4H, Ph).

13

C{1H}

NMR (DMSO-d6, ppm): δ 165.9, 150.1, 140.3, 133.8, 132.0, 128.4, 127.8, 111.1. HRMS (ESI-orbitrap) m/z: [M+Na]+ Calcd for C19H15N3O2Na 340.1056; Found 340.1055. • N,N’-(Pyridine-2,6-diyl)bis(4-methoxybenzamide) (3d) To an ice-cooled THF (150 mL) solution of 2,6-diaminopyridine (7.34 g, 67.2 mmol) and NEt3 (23 mL, 17 g, 170 mmol) was added a THF (70 mL) solution of 4-methoxybenzoyl chloride (25.3 g, 148 mmol) dropwise. After the addition was completed, the reaction mixture was allowed to 29



warm to room temperature and stirred overnight. The reaction mixture was poured into 300 mL H2O. The mixture was extracted by CH2Cl2 (2 × 200 mL). The combined organic layer was washed by H2O (1 × 100 mL), saturated NaHCO3 aq. (1 × 100 mL), again H2O (1 × 100 mL) and brine (1 × 100 mL). Then the organic layer was dried over MgSO4. After filtration, the solvents were evaporated. Recrystallization of the residual solid from EtOH (80 °C) afforded 3d as an off-white crystal (11.8 g, 31.3 mmol, 47% isolated yield). 1H NMR (DMSO-d6, ppm): δ 10.21 (br s, 2H, NH), 8.03 (d, J = 8.7 Hz, 4H, Ph), 7.85 (br, 3H, Py), 7.04 (d, J = 8.7 Hz, 4H, Ph), 3.83 (s, 6H, OCH3). 13C{1H} NMR (DMSO-d6, ppm): δ 164.9, 162.2, 150.5, 139.7, 129.7, 126.0, 113.6, 110.7, 55.3. HRMS (ESI-orbitrap) m/z: [M+Na]+ Calcd for C21H19N3O4Na 400.1268; Found 400.1266. • N,N’-(Pyridine-2,6-diyl)bis(4-(diphenylamino)benzamide) (3e) 4-Diphenylaminobenzoic acid, a precursor, was synthesized according to the literature procedure8. 4-(Diphenylamino)benzaldehyde (5.3 g, 19 mmol) was dispersed in a mixed solvent of acetone (120 mL) and water (30 mL). To the refluxed reaction mixture was added potassium permanganate (13 g, 82 mmol) in three portions. After being heated for 4 h, the reaction mixture was allowed to cool to room temperature. Acetone was removed by a rotary evaporator. To the residual solid was added water (100 mL) and the crude solid was filtered to remove a brown precipitate (MnO2). 1 M HCl (100 mL) was added to the filtrate and a pale yellow solid appeared. The yellow solid was collected by filtration and dried in a vacuum oven (90 °C, 10 h). Then, 4-diphenylaminobenzoic acid (4.85 g, 16.8 mmol, 87% isolated yield) was obtained. The spectroscopic data were consistent with those reported in the literature.

30


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To CH2Cl2 (25 mL) solution of 4-diphenylaminobenzoic acid (1.42 g, 4.90 mmol) was slowly added oxalyl chloride (1.29 mL, 1.90 g, 15.0 mmol) and subsequently DMF (0.05 mL). After the reaction mixture was stirred for 16 h, volatiles were removed in vacuo to give a yellowish brown solid. To the solid was added THF (15 mL), and the resultant solution was slowly added to an ice-cooled THF (15 mL) solution of 2,6-diaminopyridine (0.251 g, 2.30 mmol) and triethylamine (0.8 mL, 0.6 g, 6 mmol). The formation of precipitate was observed. After 2 h, the ice bath was removed and the reaction was allowed to warm to room temperature. The reaction mixture was stirred for 24 h before it was filtered to remove the precipitate. The filtrate was evaporated to afford a stained yellow solid, which was subjected to column chromatography on silica gel (eluent: hexane / ethyl acetate = 5: 1 (v/v), Rf = 0.55). The yellow crystalline solid was obtained and it was dissolved in CH2Cl2 and reprecipitation was performed in hexane. After filtration, the product was obtained as a yellowish powder (0.915 g, 1.40 mmol, 61% isolated yield). 1

H NMR (CDCl3, ppm): δ 8.34 (br s, 2H, NH), 8.09 (d, J = 8.1 Hz, 2H, Py), 7.75 (d, J = 8.8 Hz,

4H, Ph), 7.31 (m, 8H, Ar), 7.14 (m, 11H, Ar). 7.05 (d, J = 8.8 Hz, 4H, Ph) 13C{1H} NMR (CDCl3, ppm): δ 164.9, 151.6, 150.0, 146.7, 140.9, 129.6, 128.4, 125.8, 125.8, 124.5, 120.5, 109.5. HRMS (ESI-orbitrap) m/z: [M+Na]+ Calcd for C43H33N5O2Na 674.2526; Found 674.2532. • N,N’-(Pyridine-2,6-diyl)bis(2,2-dimethylpropanamide) (3f) An ice-cooled THF (50 mL) solution of 2,6-diaminopyridine (3.28 g, 30.0 mmol) and NEt3 (10 mL, 7.6 g, 75 mmol) was stirred. To the solution was added a THF (20 mL) solution of pivaloyl chloride (8.0 mL, 8.0 g, 66 mmol) dropwise. The reaction mixture was allowed to warm to room temperature and stirred for 12 h. Then the solvents were evaporated. The residue was purified by column chromatography on silica gel (eluent: hexane / EtOAc = 4:1 (v/v), Rf = 0.43) to afford 3f 31



Page 32 of 54

as a colorless solid (8.09 g, 29.2 mmol, 97% isolated yield). 1H NMR (CDCl3, ppm): δ 7.93 (d, J = 8.1 Hz, 2H, Ar), 7.76 (br s, 2H, NH), 7.69 (t, J = 8.1 Hz, 1H, Ar), 1.32 (s, 18H, tBu). 13C{1H} NMR (CDCl3, ppm): δ 176.9, 149.8, 140.9, 109.4, 39.9, 27.6. HRMS (ESI-orbitrap) m/z: [M+Na]+ Calcd for C15H23N3O2Na 300.1682; Found 300.1676.

• N,N’-(Pyridine-2,6-diyl)bis(4-(tert-butyl)benzamide) (3g) An ice-cooled THF (50 mL) solution of 2,6-diaminopyridine (3.28 g, 30.0 mmol) and NEt3 (10 mL, 7.6 g, 75 mmol) was stirred. To the solution was added a THF (20 mL) solution of 4-(tert-butyl)benzoyl chloride (12 mL, 13 g, 66 mmol) dropwise. The reaction mixture was allowed to warm to room temperature and stirred for 16 h. Then the reaction mixture was filtered to remove the precipitate. The solvents were evaporated to give a colorless solid. The residue was purified by recrystallization from hexane and EtOAc to afford 3g as a colorless solid (5.88 g, 13.7 mmol, 46% isolated yield). 1H NMR (DMSO-d6, ppm): δ 10.40 (br s, 2H, NH), 7.96 (d, J = 8.7 Hz, 4H, Ph), 7.88 (m, 3H, Py), 7.53 (d, J = 8.7 Hz, 4H, Ph), 1.31 (s, 18H, tBu).

13

C{1H} NMR

(DMSO-d6, ppm): δ 165.5, 154.9, 150.5, 139.9, 131.2, 127.8, 125.3, 111.0, 34.7, 30.9. HRMS (ESI-orbitrap) m/z: [M+Na]+ Calcd for C27H31N3O2Na 452.2308; Found 452.2309.

General procedure for the syntheses of 2,5-disubstituted-1,3,4,6,9b-pentaazaphenalenes. An accurate of the reagents and the differences between the substrates are described for each compound. Typical procedure was as follows. A and B (the reaction times) are described in Table S28 in Supporting Information. 32


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A toluene (5 mL) solution of 3a-g (1 mmol) and PCl5 (3 mmol, PCl3 was used for the synthesis of 3e) was refluxed for A. Although amides are usually insoluble in toluene at the initial state, the homogenous solutions were obtained as the reaction proceeded. Then the reaction mixture was cooled to 80 °C and volatiles were removed in vacuo at 80 °C. The residue was re-dissolved in 10 mL CH2Cl2. To the solution was added Et2O (5 mL) solution of cyanamide (10 mmol). The solution was stirred at 40 °C for B. The details of purification are described in following sections.

Syntheses of 2,5-substituted-5APs (2a,b and 4a-e). • 2,5-di-tert-butyl-1,3,4,6,9b-pentaazaphenalene (2a) Reagents: 3f (2.79 g, 10.1 mmol), PCl5 (6.72 g, 32.3 mmol) and cyanamide (4.29 g, 102 mmol). Purification: The reaction mixture was cooled to room temperature after 14 h of heating. CH2Cl2 was added and the mixture was filtered to remove insoluble byproducts. The solvents were removed in vacuo, then the residue was dissolved in CH2Cl2 (200 mL). The solution was washed by H2O (3 × 150 mL) and brine (1 × 100 mL). The organic layer was dried over MgSO4, filtered and evaporated. Recrystallization of the residue from hexane afforded 2a as a red crystalline solid (1.98 g, 6.98 mmol, 69% isolated yield) after washing by cold hexane and H2O. 1

H NMR (CDCl3, ppm): δ 7.13 (t, J = 8.3 Hz, 1H, Ar), 6.02 (d, J = 8.3 Hz, 2H, Ar), 1.16 (s, 18H,

tBu).

13

C{1H} NMR (CDCl3, ppm): δ 186.6, 161.2, 155.0, 145.1, 110.8, 39.2, 27.9. HRMS

(ESI-orbitrap) m/z: [M+H]+ Calcd for C16H22N5 284.1870; Found 284.1863.

33



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• 2,5-Bis(4-tert-butylphenyl)-1,3,4,6,9b-pentaazaphenalene (2b) Reagents: 3g (0.435 g, 1.01 mmol), PCl5 (0.617 g, 2.96 mmol) and cyanamide (0.426 g, 10.1 mmol). Purification: The reaction mixture was cooled to room temperature after 10 h of heating. The solution was filtered to remove orange insoluble byproducts. The precipitate was washed by CHCl3. The filtrate was evaporated to afford a purple solid. Recrystallization of the purple solid from CHCl3 / MeOH (60 °C) afforded 2b as a purple powder (0.314 g, 0.721 mmol, 71% isolated yield). 1H NMR (CDCl3, ppm): δ 8.18 (d, J = 8.8 Hz, 4H, Ph), 7.43 (d, J = 8.8 Hz, 4H, Ph), 7.30 (t, J = 8.3 Hz, 1H, 5AP), 6.22 (d, 2H, J = 8.3 Hz, 5AP). 13C{1H} NMR (CDCl3, ppm): δ 170.9, 161.1, 156.6, 155.1, 145.1, 131.8, 128.9, 125.1, 111.1, 35.1, 31.2. HRMS (ESI-orbitrap) m/z: [M+Na]+ Calcd for C28H29N5Na 458.2315; Found 458.2322. • 2,5-Bis(4-cyanophenyl)-1,3,4,6,9b-pentaazaphenalene (4a) Reagents: 3a (0.380 g, 1.03 mmol), PCl5 (0.653 g, 3.14 mmol) and cyanamide (0.481 g, 11.4 mmol). Purification: The reaction mixture was cooled to room temperature after 21 h of heating. The reaction mixture was passed through a silica pad with an eluent of CHCl3. Greenish blue solution was collected and the solvent was removed in vacuo to give a green solid. Recrystallization of the green solid from CHCl3 / MeOH / hexane (60 °C) afforded 4a as a green powder (0.148 g, 0.397 mmol, 38% isolated yield). 1H NMR (CDCl3, ppm): δ 8.31 (d, J = 8.6 Hz, 4H, Ph), 7.71 (d, J = 8.6 Hz, 4H, Ph), 7.39 (t, J = 8.3 Hz, 1H, 5AP), 6.30 (d, 2H, J = 8.3 Hz, 5AP).

34


13

C{1H} NMR

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(CDCl3, ppm): δ 170.0, 155.3, 146.0, 138.3, 132.0, 129.3, 118.2, 116.2, 112.8, 111.6. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C22H12N7 374.1146; Found 374.1149. • 2,5-Bis(4-(trifluoromethyl)phenyl)-1,3,4,6,9b-pentaazaphenalene (4b) Reagents: 3b (0.450 g, 0.99 mmol), PCl5 (0.644 g, 3.09 mmol) and cyanamide (0.45 g, 11 mmol). Purification: The reaction mixture was cooled to room temperature after 14 h of heating. The solution was filtered to remove orange insoluble byproducts. The filtrate was evaporated to afford green solid. The residual solid was recrystallized from CHCl3 / MeOH (60 °C) to give 4b as a green crystal (0.11 g, 0.23 mmol, 23% isolated yield). 1H NMR (CDCl3, ppm): δ 8.33 (d, J = 8.16 Hz, 4H, Ph), 7.67 (d, J = 8.16 Hz, 4H, Ph), 7.37 (t, J = 8.22 Hz, 1H, 5AP), 6.29 (d, 2H, J = 8.22 Hz, 5AP). 13C{1H} NMR (CDCl3, ppm): δ 170.2, 161.9, 155.2, 145.8, 137.5, 134.2 (q, J = 32 Hz), 129.2, 123.8 (q, J = 272 Hz), 125.1 (m) 112.4. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C22H12F6N5 460.0991; Found 460.0986.

• 2,5-Diphenyl-1,3,4,6,9b-pentaazaphenalene (4c) Reagents: 3c (0.338 g, 1.06 mmol), PCl5 (0.672 g, 3.23 mmol) and cyanamide (0.469 g, 11.2 mmol). Purification: The reaction mixture was cooled to room temperature after 19 h of heating. CHCl3 (ca. 10 mL) was added to dilute the reaction mixture. The solution was filtered to remove orange insoluble byproducts. The filtrate was evaporated to afford purple solid. The residual solid was recrystallized from CHCl3 / MeOH (60 °C) to give 4c as a blue powder (0.26 g, 0.80 mmol, 35



75% isolated yield). 1H NMR (CDCl3, ppm): δ 8.25 (d, J = 8.8 Hz, 4H, Ph), 7.53 (t, J = 7.4 Hz, 2H, Ph), 7.42 (m, 4H, Ph), 7.31 (t, J = 8.4 Hz, 1H, 5AP) 6.24 (d, 2H, J = 8.4 Hz, 5AP). 13C{1H} NMR (CDCl3, ppm): δ 171.1, 161.3, 153.1, 145.3, 134.5, 132.8, 129.0, 128.1, 111.5. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C20H14N5 324.1244; Found 324.1238.

• 2,5-Bis(4-methoxyphenyl)-1,3,4,6,9b-pentaazaphenalene (4d) Reagents: 3d (0.385 g, 1.02 mmol), PCl5 (0.611 g, 2.93 mmol) and cyanamide (0.456 g, 10.8 mmol). Purification: The reaction mixture was cooled to room temperature after 10 h of heating. CHCl3 and MeOH (ca. 10 mL) were added to dilute the reaction mixture. The solution was filtered to remove orange insoluble byproducts. The filtrate was evaporated to afford purple solid. The residual solid was recrystallized from CHCl3 / hexane (60 °C) to give 4d as a blue powder (0.29 g, 0.75 mmol, 73% isolated yield). 1H NMR (CDCl3, ppm): δ 8.24 (d, J = 9.0 Hz, 4H, Ph), 7.30 (t, J = 8.2 Hz, 1H, 5AP), 6.91 (d, J = 9.0 Hz, 4H, Ph), 6.20 (d, J = 8.2 Hz, 2H, 5AP) 3.87 (s, 6H, OCH3).

13

C{1H} NMR (CDCl3, ppm): δ 170.0, 163.7, 154.9, 145.0, 131.2, 127.1, 126.0,

113.5, 110.6, 55.4. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C22H18N5O2 384.1455; Found 364.1447. • 2,5-Bis(4-(diphenylamino)phenyl)-1,3,4,6,9b-pentaazaphenalene (4e) Reagents: 3e (0.653 g, 1.00 mmol), PCl3 (5 mL of 0.6 M stock solution, 3 mmol) and cyanamide (0.424 g, 10.1 mmol).

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Purification: The reaction mixture was cooled to room temperature after 12 h of heating. The solution was filtered to remove orange insoluble byproducts. The precipitate was washed by 50 mL of CH2Cl2. The filtrate was evaporated to afford black green solid. The residual solid was purified by column chromatography on silica gel (eluent: CH2Cl2) and then precipitated from CH2Cl2 solution to MeOH to give 4e as a green powder (2.2 mg, 0.0033 mmol, 0.3 % isolated yield). 1H NMR (CD2Cl2, ppm): δ 8.04 (d, J = 9.0 Hz, 4H, Ph), 7.33 (dd, J = 7.0 Hz and 8.8 Hz, 8H, Ph), 7.30 (t, J = 8.3 Hz, 1H, 5AP), 7.15 (m, 12H, Ph), 6.96 (d, J = 9.0 Hz, 4H, Ph), 6.16 (d, J = 8.3 Hz, 2H, 5AP).

13

C{1H} NMR (CD2Cl2, ppm): δ 169.4, 155.0, 152.6, 146.9, 145.3, 130.6,

130.2, 129.9, 127.0, 126.4, 125.0, 119.9, 110.6. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C44H32N7 658.2714; Found 658.2689.

37



Bromination of 2a. • 7,9-Dibromo-2,5-di-tert-butyl-1,3,4,6,9b-pentaazaphenalene (5) A CH2Cl2 (20 mL) solution of 2 (0.285 g, 1.01 mmol) and N-bromosuccinimide (0.378 g, 2.12 mmol) was refluxed for 23 h. The solvents were removed in vacuo, then the residual solid was purified by column chromatography on silica gel (eluent: CHCl3 / hexane = 1:1 (v/v)). Recrystallization from hexane of the residual solid after evaporation afforded 5 as a purple fiber crystal (0.37 g, 0.83 mmol, 82% isolated yield). 1H NMR (CDCl3, ppm): δ 7.77 (s, 1H, 5AP), 1.21 (s, 18H, tBu). 13C{1H} NMR (CDCl3, ppm): δ 188.0, 161.1, 151.4, 150.0, 102.4, 39.8, 27.9. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C16H20Br2N5 440.0080; Found 440.0078.

General procedure of the Suzuki-Miyaura cross coupling reactions for 6a-e. To a toluene (1 mL) solution of 5 (0.10 mmol), arylboronic acid or arylboronic acid pinacol ester (0.21 mmol), SPhos Pd G3 (10 μmol) and cesium carbonate (1.0 mmol) (an accurate amount of the reagents is described below) was added degassed water (1 mL). The mixture was stirred at 85 °C overnight. The reaction mixture was allowed to cool to room temperature and diluted by CHCl3 (30–50 mL). The organic phase was washed by H2O (3 × 20–50 mL) and brine (1 × 10–30 mL). The organic phase was dried over MgSO4. After filtration, the solvent was removed by a rotary evaporator. The crude material was purified by column chromatography on silica gel

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(eluent: CHCl3) and then the solvent was evaporated to give the products. An accurate amount of the reagents and the reaction time is described below for each compound.

Syntheses of 7,9-substituted 5APs (6a-e). •7,9-Bis(4-cyanophenyl)-2,5-di(tert-butyl)-1,3,4,6,9b-pentaazaphenalene (6a) From 5 (44.15 mg, 0.10 mmol), 4-cyanophenylboronic acid pinacol ester (49.24 mg, 0.21 mmol), SPhos Pd G3 (8.54 mg, 0.011 mmol) and Cs2CO3 (332 mg, 1.0 mmol), the product was obtained as a purple solid (0.045 g, 0.093 mmol, 93% isolated yield). Rf = 0.20 (CHCl3). 1H NMR (CDCl3, ppm): δ 7.67 (br, 8H, Ph), 7.77 (s, 1H, 5AP), 1.14 (s, 18H, tBu). 13C{1H} NMR (CDCl3, ppm): δ 187.3, 153.0, 146.0, 139.9, 132.2, 129.5, 120.4, 119.0, 111.9, 92.5, 39.9, 28.0. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C30H28N7 486.2401; Found 486.2390.

•7,9-Bis((4-trifluotromethyl)phenyl)-2,5-di(tert-butyl)-1,3,4,6,9b-pentaazaphenalene (6b) From 5 (42.67 mg, 0.097 mmol), 4-(trifluoromethyl)phenylboronic acid pinacol ester (56.85 mg, 0.21 mmol), SPhos Pd G3 (7.70 mg, 0.0099 mmol) and Cs2CO3 (296 mg, 0.91 mmol), the product was obtained as purple solid (0.039 g, 0.068 mmol, 70% isolated yield). Rf = 0.60 (CHCl3). 1H NMR (CDCl3, ppm): δ 7.65 (m, 8H, Ph), 7.55 (s, 1H, 5AP), 1.13 (s, 18H, tBu). C{1H} NMR (CDCl3, ppm): δ 187.0, 162.4, 152.9, 146.3, 139.2, 130.0 (q, J = 32 Hz), 129.3,

13

39



124.6 (q, J = 271 Hz), 125.2 (q, 3.9 Hz), 120.9, 39.9, 28.0. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C30H28F6N5 572.2243; Found 572.2236.

•7,9-Diphenyl-2,5-di(tert-butyl)-1,3,4,6,9b-pentaazaphenalene (6c) From 5 (45.15 mg, 0.102 mmol), phenylboronic acid pinacol ester (47.94 mg, 0.21 mmol), SPhos Pd G3 (8.17 mg, 0.010 mmol) and Cs2CO3 (365 mg, 1.1 mmol), the product was obtained as a purple solid (0.041 g, 0.091 mmol, 90% isolated yield). Rf = 0.30 (CHCl3). 1H NMR (CD2Cl2, ppm): δ 7.52–7.58 (m, 5H, 4H of Ph and 1H of 5AP), 7.30–7.42 (s, 6H, Ph), 1.14 (s, 18H, tBu). C{1H} NMR (CD2Cl2, ppm): δ 186.2, 162.7, 152.2, 146.48, 146.45, 135.6, 128.8, 128.3, 122.5,

13

39.7, 28.0. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C28H30N5 436.2496; Found 436.2485.

•7,9-Bis(4-methoxyphenyl)-2,5-di(tert-butyl)-1,3,4,6,9b-pentaazaphenalene (6d) From 5 (44.87 mg, 0.102 mmol), 4-methoxyphenylboronic acid (32.30 mg, 0.21 mmol), SPhos Pd G3 (8.46 mg, 0.011 mmol) and Cs2CO3 (358 mg, 1.1 mmol), the product was obtained as a blue solid (0.037 g, 0.074 mmol, 73% isolated yield). Rf = 0.15 (CHCl3). 1H NMR (CD2Cl2, ppm): δ 7.38 (d, J = 8.6 Hz, 4H, Ph), 7.37 (s, 1H, 5AP), 6.80 (d, J = 8.6 Hz, 4H, Ph), 3.72(s, 6H, OCH3), 1.04 (s, 18H, tBu).

13

C{1H} NMR (CD2Cl2, ppm): δ 185.9, 162.8, 159.8, 151.6, 145.6,

130.1, 127.9, 122.2, 113.6, 55.7, 39.6, 28.0. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C30H34N5O2 496.2707; Found 496.2694.

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•7,9-Bis((4-N,N-dimethylamino)phenyl)-2,5-di(tert-butyl)-1,3,4,6,9b-pentaazaphenalene (6e) From 5 (45.49 mg, 0.103 mmol), 4-(N,N-dimethylamino)phenylboronic acid pinacol ester (57.77 mg, 0.21 mmol), SPhos Pd G3 (7.95 mg, 0.010 mmol) and Cs2CO3 (310 mg, 0.95 mmol), the product was obtained as a green solid (0.049 g, 0.093 mmol, 90% isolated yield). Rf = 0.15 (CHCl3). 1H NMR (CD2Cl2, ppm): δ 7.50 (s, 1H, 5AP), 7.45 (d, J = 8.9 Hz, 4H, Ph), 6.71 (d, J = 8.9 Hz, 4H, Ph), 2.98 (s, 12H, N(CH3)2), 1.15 (s, 18H, tBu).

13

C{1H} NMR (CD2Cl2, ppm): δ

185.2, 163.1, 150.8, 150.6, 144.7, 129.6, 127.0, 123.2, 122.9, 111.8, 40.6 (br), 39.5, 28.1. Some peaks were split in high concentration presumably due to aggregation of the compound. HRMS (ESI-orbitrap) m/z: [M+H]+ Calcd for C32H40N7 522.3340; Found 522.3333.

41



Acknowledgment This work was supported by The Ogasawara Foundation for the Promotion of Science & Engineering (for K.T.), a Grant-in-Aid for Scientific Research (B) (JP17H03067), for Scientific Research on Innovative Areas “New Polymeric Materials Based on Element-Blocks (No.2401)” (JP24102013), for Challenging Research (Pioneering) (JP18H05356) and for JSPS Fellows (for H.W., JSPS KAKENHI Grant Number JP 17J07338).

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Supporting Information Supporting Information: Crystallographic information for 2a (CIF) Details of designing the reaction toward 5AP, copies of 1H and

13

C{1H} NMR spectra,

conditions and results of DFT (cartesian coordinates of optimized structure of 2a, 4a-e and 6a-e) and TD-DFT (detailed assignment of the excited states of 2a, 4a-e and 6a-e) calculation, crystallographic data of 2a (PDF)

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Independently Tuned Frontier Orbital Energy Levels of 1,3,4,6,9b

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