In April 2022, Osaka City University and Osaka Prefecture University marge to Osaka Metropolitan University

A fused polycyclic compound containing
phenothiazine and diazapyrene skeletonswith weak D–A interactions
Keito Matsumoto, Yoshimitsu Tachi, Masatoshi Kozaki
Citation

Chemical Communications. 58(61); 8572-8575.

Issue Date2022-08-07

Published2022-07-02

TypeTextversion

Journal Article
Author
The following article has been accepted by Chemical Communications.

Relation

The final, published version is available at https://doi.org/10.1039/D2CC02635J.
Please cite only the published version.

SupplementarySupplementary files is available at https://doi.org/10.1039/D2CC02635J.

files
DOI

10.1039/D2CC02635J

Self-Archiving by Author(s)Placed on: Osaka City University

Matsumoto, K., Tachi, Y., & Kozaki, M. (2022). A fused polycyclic compound containing
phenothiazine and diazapyrene skeletons with weak D–A interactions. Chemical Communications.
58, 8572–8575. https://doi.org/10.1039/d2cc02635j

COMMUNICATION
Fused Polycyclic Compound Containing Phenothiazine andDiazapyrene Skeletons with Weak D-A interactions
Received 00th January 20xx,
Accepted 00th January 20xx

Keito Matsumoto, Yoshimitsu Tachi and Masatoshi Kozaki*

DOI: 10.1039/x0xx00000x

A small fused polycyclic molecule containing a phenothiazine anddiazapyrene skeleton as the donor and acceptor, respectively, hasa redox potential similar to those of the corresponding donor andacceptor molecules, indicating that the inherent electronic
properties of the donor and acceptor were retained due to weakorbital interactions.
Phenothiazines (PTZs) are considered excellent electron-richbuilding blocks for the construction of electronic,1 optical,2 andmagnetic materials.3 Recently, a variety of PTZ-based extended
fused-ring systems have been produced by condensing
electron-rich rings to enhance their electron-donating ability(A–C, Fig. 1).4 There are a few donor (D)-acceptor (A)-type
fused-ring compounds with a PTZ framework and electrondeficient conjugating rings.5 In sharp contrast, PTZ units areoften connected to A-units with single bonds or conjugatedbridges to obtain advanced functional materials, such as photoemitters with thermally activated delayed emission or photoinduced charge-separating systems.6
For some applications, weak intramolecular D–Ainteractions, and spatial separation of the HOMO and LUMO areessential for obtaining the desired function of the D–A typemolecule.7 D–A-type fused-ring systems with flat structures
facilitate strong intermolecular π–π interactions. The proximityof the electron-rich and electron-poor rings, however, usuallyinduces strong D–A interactions in the ground state, resulting in
the attenuation of electron donating and accepting abilities andlarge HOMO–LUMO energy gaps.8 Recently, Hatakeyama et al.
achieved an efficient HOMO–LUMO separation with multiple
resonance effects.9 Their research revealed that small D–A typefused-ring systems with weak HOMO–LUMO interaction can beproduced by suitably conjugated topologies. However, smallGraduate School of Science, Osaka City University 3-3-138, Sugimoto,Sumiyoshi-ku, Osaka 558-8585, Japan†Electronic Supplementary Information (ESI) available: [Syntheticprocedures, NMR spectra, cetacean coordinate of optimizedstructures.]. See DOI: 10.1039/x0xx00000x

Fig. 1. Representative phenothiazine-based fused-ring compounds and this work.

polycyclic fused compounds with weak intramolecular D–Ainteractions are limited, and a conjugation topology suitable for
reducing the D–A interactions has not yet been established.
Herein, we report the compact fused-ring system 1 with PTZ
and diazapyrene (DAP) units joined by one benzene ring as thedonor and acceptor, respectively. In previous studies, extensionof the conjugation was often achieved using an aromatic ring at
a nitrogen atom in the PTZ unit (Fig.1).4 This is a rare example of
π-extension of the PTZ unit with an aromatic ring connected atthe 3-position, followed by double annulation at the 2- and 4positions. The structure and properties of 1 were investigatedby means of X-ray structural analyses, spectral andelectrochemical measurements, and theoretical calculations,and the results indicate that the inherent electron-donating andelectron-accepting abilities of the PTZ and DAP skeletons,
respectively, are unexpectedly retained in the fused-ring system
due to the unique conjugation topology.

COMMUNICATION
Scheme 1. Synthesis of 1.

Compound 1 was synthesized from 3-bromo-10-(4methylphenyl)-10H-PTZ (2) using a previously reported doubleannulation protocol (Scheme 1).10 Compound 2 was prepared in
two steps from the easily accessible 10H-phenothiazine using apreviously reported method.11 Direct C–H arylation ofisophthalonitrile (3) with 2 was carried out using palladium
acetate, tri(cyclohexyl)phosphine (Cy3P), potassium carbonate,
and 2-ethylhexanolic acid to produce 4 in 55% yield.12 The
nucleophilic addition of 4-methylphenylmagnesium bromide to
4 followed by treatment with methanol, formed bisimine 5 in
54% yield.13 Compound 1 was obtained as a purple solid in 52%
yield by copper-catalyzed oxidative double transannularcyclization of 1.10,13 PTZ was successfully converted to 1 in only
five steps. The structure of 1 was characterized in a detailed
manner using NMR spectroscopy, MS analysis, and X-raystructural analysis.
A single crystal of 1 suitable for X-ray structural analysis wasobtained as a black plate by slow vapor diffusion of diethyl ether
into a dichloromethane solution of 1 (Fig. 2 and Table S1).
Although neutral PTZ units typically have a butterfly structure in
the solid state14, the fused-ring framework of 1 unpredictably
has an almost planar structure with a slight bend. The dihedral

Fig. 2. ORTEP diagrams of 1: (a) Top view, (b) Side view (Blue, yellow, grey, andwhite shows nitrogen, sulfur, and carbon atoms, respectively. 4-Methyl phenylgroups and hydrogen atoms were omitted for clarity. Italic symbols denoteassigned names of the selected bonds and ring positions.

2 | J. Name., 2012, 00, 1-3

Journal Name
angle (φ) between the benzene rings in the PTZ unit in 1 is 170 °,which is significantly larger than that in 10-phenyl-10Hphenothiazine (6, φ = 153 °, Fig. 3).15 Neutral PTZ skeletons withrelatively planar conformations were reported for some PTZbased D–A type molecules, such as C (φ = 175 °).5,16 The C–S(1.763(2) and 1.756(2) Å) and C–N (1.408(3) and 1.420(2) Å)bond lengths in ring B are typical of the neutral PTZ unit.14,15 TheC–N (imine) bonds e (1.386(2) Å) and f (1.386(2) Å) are similarin length to the closely related DAP derivative (1.40 Å).17 In thecrystal, 1 formed a slipped-stacking structure in a head-to-headand tail-to-tail fashion (Fig. S1) that involved intermolecular C–C contacts (3.32 and 3.38 Å), slightly shorter than the sum of thevan der Waals radii (3.40 Å). The substituted tolyl groups in theDAP unit had large dihedral angles with the adjacent rings D andE (43.0° and 42.3°).
The UV-Vis spectrum of 1 was measured at room
temperature in dichloromethane (ε = 8.9, 4.53 × 10-5 M) andcomparedwith
thoseof10-(4-methylphenyl)-10Hphenothiazine (7) and 5,9-di(4-methylphenyl)-4,10-diazapyrene(8) to gain insight into the electronic structure in the groundstate (Fig. 4). Compound 1 produced a characteristic broad
absorption band in the visible region, with maximum absorption(λabsmax) at 522 nm. Absorption band for 7 and 8 were observedin the shorter-wavelength region up to 400 nm. Timedependent density functional theory (DFT) calculations at theCAM-B3LYP/6-31+g(d,p) level of theory were performed toassign the absorption band of 1 in the visible region (λcalcdmax =451 nm, f = 0.1625), indicating that the HOMO–LUMO transitionis the dominant contributor to this electronic transition. As
described below, the DFT calculation results suggested that theHOMO and LUMO are found predominantly on the PTZ and DAPunits, respectively. Therefore, the HOMO–LUMO band wascharacterized by short-range intramolecular charge transfer(ICT). The optical HOMO–LUMO energy gap (Egopt) wasestimated to be 2.00 eV from the terminal wavelength of longwavelength absorption (619 nm). The absorption spectra of 1
were recorded in toluene (ε = 2.4, 3.07 × 10-5 M) and DMF (36.7,3.29 × 10-5 M) (Fig. S2). The λabsmax of the ICT band was slightly
blue-shifted by 11 nm upon increasing the solvent polarity(λabsmax = 516 (toluene,) and 527 (DMF)), indicating that 1 has asmall dipole moment in the ground state. These results suggest
the presence of a weak interaction between the PTZ and DAP
units in the ground state. The calculated dipole moment (2.51D) further supported the weakly polar character of 1 in theground state.
To determine the electronic structure in the excited state,
the fluorescence spectrum of 1 was measured at room
temperature (Fig. S3). Considerable red shifts were observed forFig. 3. Chemical structures of reference compounds.

This journal is © The Royal Society of Chemistry 20xx

Journal NameCOMMUNICATION

Fig. 4. UV-Vis spectra of 1 (red line, 4.53 × 10-5 M), 7 (blue line), and 8 (green line)
in dichloromethane.

the fluorescence band of 1 when the solvent polarity wasincreased. Fluorescence maxima (λemmax) were observed at 620,636, and 648 nm in toluene (λex = 526 nm, Φf = 0.26),
dichloromethane (green line, λex = 522 nm, Φf = 0.091), and DMF(blue line, λex = 526 nm, Φf = 0.058), respectively. Therefore, theStokes shift increased with increasing the solvent polarity (3250
cm-1 (toluene), 3430 (dichloromethane), and 3540 (DMF)).
These results indicate that 1 has a larger dipole moment in theexcited state than in the ground state.18
Cyclic voltammograms of 1 were measured in benzonitrile
using tetrabutylammonium perchlorate (nBu4NClO4), a Pt disk
electrode, and Pt wire as the supporting electrolyte, working
electrode, and counter electrode, respectively, at a scan rate of
100 mV/s. Reversible oxidation and reduction waves wereobserved at half-wave potentials (E1/2) of +0.35 and −1.88 V vsFc/Fc+, respectively (Fig. 5). The oxidation potential of 1 wascomparable to that of 7 (E1/2ox = +0.37 V vs Fc/Fc+),19 indicatingthat the electron-donating ability of the PTZ unit wasmaintained in the fused-ring system of 1. The HOMO energy
level of 1 was estimated to be −5.15 eV from the oxidation
potential. However, the reduction potential of 1 cathodicallyshifted 0.25 V compared to that of 8 (E1/2red = −2.13 V vsFc/Fc+),19 suggesting that the inherent electron-accepting abilityof the DAP unit was retained in the fused-ring system in 1. TheLUMO energy level of 1 was calculated to be −2.92 eV using thereduction potentials. The electrochemical HOMO–LUMOFig. 6. Energy diagrams of the Kohn–Sham HOMOs and LUMOs of 1, 7, and 8
obtained from DFT calculations (B3LYP/6-31G(d,p)).

energy gap (Egec) was determined to be 2.23 eV, which wasconsistent with Egopt (2.00 eV).
To determine the detailed features of the frontier orbitals,
DFT calculations were performed at the B3LYP/6-31G(d,p) levelof theory for 1 and 7. The results were compared with thosereported for 8 (Fig. 6). The HOMO energy level of 1 wascalculated to be −4.70 eV, which is comparable to that of 7(−4.89 eV), indicating that the PTZ units in 1 maintain theirinherent electron donating ability. The LUMO energy level of 1was estimated to be −1.95 eV, which is very similar to that of 8(−2.00 eV), suggesting that 1 has an electron-accepting ability
comparable to that of 8. The HOMO and LUMO of 1 are
predominantly localized on the PTZ and DAP units, respectively.
The distinct orbital shapes of the HOMO of 7 and the LUMO of
8 are reminiscent of the HOMO and LUMO of 1, respectively.
These results suggest the presence of weak intramolecularinteractions between the PTZ and DAP units in 1. The narrow
HOMO–LUMO gap (2.75 eV) was evaluated for 1 because theHOMO and LUMO energy levels of 1 are almost the same as
those of 7 and 8, respectively. This value is slightly larger thanthe experimentally obtained values (Egopt: 2.00 eV, Egec: 2.23 eV).
The aromaticities of 1 and 6 were evaluated by calculating
nucleus-independent chemical shifts (NICS) using the GAOCAM-B3LYP/6-31G+(d,p) level of theory (Fig. 7 and Table S4).
The initial geometries were extracted from the respective
crystal structures. The NICS(0) value for hetero six-memberedring B of 1 were +8.43, which are considerably higher than thoseFig. 5. Cyclic voltgammogram of 1 in benzonitrile (nBu4NClO4, a Pt disk electrode,and Pt wire as a supporting electrolyte, working electrode, and counter electrode,respectively, at a scan rate of 100 mV/s.).
Fig. 7. NICS(0) values of 1 (GAO-CAMB3LYP/6-31G+(d,p)).

This journal is © The Royal Society of Chemistry 20xx

J. Name., 2013, 00, 1-3 | 3

COMMUNICATION

Journal Name
5Fig. 8. Conjugation topologies with (1) strong and (2) weak D-A interactions (X:electron rich atoms, and Y: electron poor atoms).

of 6 (+4.43). These results indicate that the structural change
from a butterfly to planar structure enhances theantiaromaticity of ring B. The inner benzene ring C in 1 has asmall NICS(0) (−9.13), which indicates that ring C possesses higharomaticity. This was further supported by the large harmonic
oscillator model of aromaticity values (0.95) of ring C. Thisconsideration is consistent with the absence of a stablequinoidal resonance structure for ring C. The weak
intramolecular D–A interaction was attributed to the lack of astable zwitterionic resonance structure of the conjugatedsystem in 1 (Fig. 8). Bridging a nitrogen atom in a diarylimine
group and an electron-donating heteroatom (X in Fig. 8) withphenylene linker is probably useful approach to reduce D–Ainteractions.
In conclusion, a compact D–A type fused-ring compound
was synthesized with PTZ and DAP units as the donors andacceptors, respectively. The PTZ and DAP units in the fused-ringsystem maintained their inherent electronic donating andaccepting abilities, respectively, owing to their unique
conjugated topology. Through this research, novel strategy fordesigning a small D–A type fused-ring system with negligible
intramolecular D–A interactions was proposed. Anothercombination of electron donating and accepting frameworks
with the similar π-topology is desired to study the scope andlimitation of the proposed strategy. Research on compoundswith similar conjugation topologies and their applications iscurrently in progress.
This work was supported by JSPS KAKENHI (Grant numbers:
JP17K05790, and JP20K05466). There are no conflicts to declare.

M. Kojima, A. Tamoto, N. Aratani, and H. Yamada, Chem.
Commun., 2017, 53, 5698.
6 R. Y. Lai, X. Kong, S. A. Jenekhe, and A. J. Bard, J. Am. Chem.
Soc., 2003, 125, 12631; H. Tanaka, K. Shizu, H. Nakanotani,and C. Adachi, J. Phys. Chem. C, 2014, 118, 15985.
7 H. Uoyama, K. Goushi, K. Shizu, H. Nomura, and C. Adachi,Nature, 2012, 492, 234.
8 Y.-J. Cheng, Y.-J. Ho, C.-H. Chen, W.-S. Kao, C.-E. Wu, S.-L.
Hsu, and C.-S. Hsu, Macromolecules, 2012, 45, 2690; C. Jia,S.-X. Liu, C. Tanner, C. Leiggener, A. Neels, L. Sanguinet, E.
Levillain, S. Leutwyler, A. Hauser, and S. Decurtins, Chem.
Eur. J., 2007, 13, 3804.
9 T. Hatakeyama, K. Shiren, K. Nakajima, S. Nomura, S.
Nakatsuka, K. Kinoshita, J. Ni, Y. Ono, and T. Ikuta, Adv.
Mater., 2016, 28, 2777.
10 Y. Omura, Y. Tachi, K. Okada, and M. Kozaki, J. Org. Chem.,
2019, 84, 2032.
11 S1. S.-H. Park, O-H. Kwon, W.-J. Paek, U.S. Patent
US20090026928 A1 2009-01-29; T. Okamoto, M. Kozaki, M.
Doe, M. Uchida, G. Wang, K. Okada, Chem. Mater., 2005, 17,5504; Y. Liang, P. Yuyu, T. Xiangyang, B. Qing, S. Fangzhong,L. Feng, L. Ping, Y. Bing M. Yuguang, J. Phys. Chem. C, 2015,119, 17800.
12 N. E. Ihanainen, E. T. T. Kumpulainen, A. M. P. Koskinen, Eur.
J. Org. Chem., 2015, 2015, 3226.
13 S. Chiba, Bull. Chem. Soc. Jpn., 2013, 86, 1400; L. Zhang, G. Y.
Ang, S. Chiba, Org. Lett., 2010, 12, 3682.
14 T. Okamoto, M. Kuratsu, M. Kozaki, D. Shiomi, K. Sato, T.
Takui, and K. Okada, Org. Lett., 2004, 6, 3493.
15 Y. Wang, J. Yang, M. Fang, Y. Gong, J. Ren, L. Tu, B. Z. Tang,and Z. Li, Adv. Funct. Mat., 2021, 31, 2101719.
16 T. Zhang, Y. Han, J. Huo, and P. Xue, CrystEngComm, 2020,22, 5137.
17 Y. Han, Z. Hu, M. Liu, M. Li, T. Wang, and Y. Chen, J. Org.
Chem., 2019, 84, 3953.
18 J. R. Lakowicz, Principles of Fluorescence Spectroscopy,Springer, Berlin, 3rd edn, 2006.
19 Redox potentials of 7 and 8 were measured under identicalconditions.

Notes and references
1234K. Kozawa, T. Hoshizaki, and T. Uchida, Bull. Chem. Soc. Jpn.,
1991, 64, 2039; H. Kobayashi, Bull. Chem. Soc. Jpn., 1973, 46,2945.
Z. Zhou, C. E. Hauke, B. Song, X. Li, P. J. Stang, and T. R. Cook,J. Am. Chem. Soc., 2019, 141, 3717; J. A. Christensen, B. T.
Phelan, S. Chaudhuri, A. Acharya, V. S. Batista, and M. R.
Wasielewski, J. Am. Chem. Soc., 2018, 140, 5290; S. Suzuki,D. Yamaguchi, Y. Uchida, and T. Naota, Angew. Chem. Int.
Ed., 2021, 60, 8284.
T. Tahara, S. Suzuki, M. Kozaki, D. Shiomi, K. Sugisaki, K. Sato,
T. Takui, Y. Miyake, Y. Hosokoshi, H. Nojiri, and K. Okada,
Chem. Eur. J., 2019, 25, 7201.
S.-i. Kato, T. Matsuoka, S. Suzuki, M. S. Asano, T. Yoshihara,
S. Tobita, T. Matsumoto, and C. Kitamura, Org. Lett., 2020,22, 734; Yokoyama, N. Tanaka, N. Fujimoto, R. Tanaka, S.
Suzuki, D. Shiomi, K. Sato, T. Takui, M. Kozaki, and K. Okada,
Chem. Asian J., 2021, 16, 72; D. Sakamaki, D. Kumano, E.
Yashima, and S. Seki, Chem. Commun., 2015, 51, 17237.

4 | J. Name., 2012, 00, 1-3

This journal is © The Royal Society of Chemistry 20xx