Design of Polar Assemblies with Bowl-shaped π-conjugated Molecules andTheir Bulk Photovoltaic EffectDaigo Miyajima1
Center for Emergent Matter Science, RIKEN
daigo.miyajima@riken.jp
Keywords: Bulk Photovoltaic Effect, Polar Assembly, Subphthalocyanine
A solar power system is indispensable technology for the realization of a sustainable society. In general, solar energy isgenerated with a photovoltaic effect using a donor-acceptor heterojunction, while a totally different type of photovoltaic effect,
known as the bulk photovoltaic effect (BPVE)1, has been attracting broad research interest. The BPVE is observed in principle innon-centrosymmetric single-crystalline materials and possesses unique features such as being ultrafast responsive and dissipationless and enabling a low noise photocurrent, which are not accessible with conventional photovoltaics. To date, the BPVE has beenstudied mainly for inorganic materials, possibly because the number of reported polar organic assemblies is limited due to the lackof rational synthetic strategies for them. Although rapid advances in the fields of supramolecular chemistry and crystal engineering
have provided a profound understanding of molecular assembly, perfectly predicting and controlling the crystal structures ofmolecules is still difficult. To the best of our knowledge, no strategy and guiding principle for designing polar single crystals suitablefor optoelectronic applications have been reported. Recently, we reported a rational strategy to form polar assemblies with bowlshaped π-conjugated molecules and a molecular design principle for this strategy2). Based on this design principle, we successfully
developed more than 12 polar crystals. Furthermore, we unveiled that the BPVE observed in these polar assemblies is generated in
the shift current mechanism. This presentation will overview the design principle and discuss the relationship between excitationand photocurrent generation3).

Figure 1. Schematic illustration of a polar assembly with bowl-shaped π-conjugated molecules.
1) C. Zhang et al., J. Am. Chem. Soc., 2020, 142, 3326. 2) C. Zhang et al., Angew. Chem. Int. Ed., 2021, 60, 3261. 3) B. Dhara, etal, to be submitted.

Organic semiconductor crystals: from low dimensional crystals to cocrystals
Wenping Hu1,2
Tianjin Key Laboratory of Molecular Optoelectronics, Tianjin University, Tianjin 300072, China(E-mail: huwp@tju.edu.cn)
The fundamental advantages of organic semiconductors have attracted the world’s attention at recent
decades and resulted in the rapid development and progress of organic electronics (or called molecularelectronics). However, there remain some key challenges in this field such as the low mobility, the notfully understanding structure-properties relationship, the absence of techniques for the fabrication of highperformance devices and circuits etc. It is prospective that high-quality single crystals of organic
semiconductors could answer these questions and further advance the development of this field. However,
the growth, characterization, and application of organic semiconductor crystals are full of challenges. Herewe will focus on organic micro- and nanocrystals, two dimensional crystals and cocrystals for a brief
introduction.

References
1.

Rongjin Li, Wenping Hu, Yunqi Liu, Daoben Zhu, Micro- and nanocrystals of organic
semiconductors, Accounts of Chemical Research, 2010, 43, 529-540.

2.

Chengliang Wang, Huanli Dong, Lang Jiang and Wenping Hu, Organic semiconductor crystals, Chem.
Soc. Rev. 2018, 47, 422-500.

3.

Fangxu Yang, Shanshan Cheng, Xiaotao Zhang, Xiaochen Ren, Rongjin Li, Huanli Dong, andWenping Hu, 2D Organic Materials for Optoelectronic Applications, Adv. Mater. 2018, 30, 1702415.

4.

Lingjie Sun, Weigang Zhu, Xiaotao Zhang, Liqiang Li, Huanli Dong and Wenping Hu, Creating
Organic Functional Materials beyond Chemical Bond Synthesis by Organic Cocrystal Engineering.
J. Am. Chem. Soc. 2021, 143, 19243−19256.

Crystal Structure Manipulation by Methylchalcogenation andIn Silico Crystallization of Brickwork-related Structures
Kirill Bulgarevich1, Kazuo Takimiya1,2,31

RIKEN CEMS, Hirosawa 2-1, Wako-shi, Saitama 351-01, Japan. 2Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi,
Japan 980-8577. 3Tohoku University IMR, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
kirill.bulgarevich@riken.jp
Keywords: Organic Semiconductors, Brickwork Crystal Structure, Crystal Structure Simulation
Organic semiconductors with crystal structures that enable two-dimensional charge transport, hold great promise forachieving high carrier mobility. Examples of such structures include herringbone, pitched-, and brickwork. Many acenes andheteroacenes such as pentacene, [1]benzothieno[3,2-b]benzothiophene (BTBT), and benzo[1,2-b:4,5-b’]dithiophene (BDT)
crystallize in herringbone structures, while pitched- and brickwork structures are less common and have only been observed inmaterials like rubrene and 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene). Recently, we discovered a way to“manipulate” the crystal structure of organic semiconductors by selectively introducing methylchalcogeno groups. For instance, byintroducing methylthio or methylseleno groups at -positions of the thiophene rings in BDT, we were able to change its herringbone
structure to a pitched- or brickwork structure.1,2 Furthermore, we found that introducing four methylthio groups into pyrene at
1,3,6,8- positions (MT-pyrene) resulted in a change from a dimeric herringbone structure to a brickwork structure (Fig. 1a), leading
to very high carrier mobility of over 30 cm2 V-1 s-1 in single-crystal organic field-effect transistors.3 However, the selenium
replacement of sulfur atoms in MT-pyrene, MS-pyrene, resulted in two structural polymorphs (Figs. 1b and 1c) with low twodimensionality and mobility inferior to MT-pyrene (up to 7.3 cm2 V-1 s-1).4 Similarly, with the core replacement to perylene frompyrene, two brickwork-related structure polymorphs were observed, but mobility was low (0.2 cm2 V-1 s-1). This highlights the needfor accurate predictions of crystal structures with the precision to discuss differences in electronic structure in the solid state.
To address this issue, we developed an “in silico crystallization (ISC)” algorithm. Unlike traditional crystal structure
prediction algorithms that consider a large number of candidate structures from a vast search range, ISC simplifies the search bylimiting it to systems in which a brickwork structure is expected. The algorithm determines the mutual positions of molecules in thecrystal by optimizing their mutual interaction through quantum chemical calculations. In brickwork structures, the molecularinteractions are hierarchical with the strongest interaction being in the -stacking (face) direction, followed by the interlayer (side)
direction and the molecular long axis (end) direction. This makes it possible to determine the molecular mutual positions in anorderly manner, rather than determining the overall structure at once (Fig. 1d). Using ISC, we were able to accurately simulate thecrystal structures of MT-, MS-pyrene, and MT-perylene, including the fine differences in the two-dimensionality between thestructures. Our algorithm even predicted the existence of a related polymorph of MT-pyrene, which was later confirmed
experimentally. This demonstrates the potential of ISC for aiding the search for high-mobility organic semiconductors.

Figure 1. Brickwork structure of (a) MT-pyrene and (b) MS-pyrene. (c) Inclined brickwork structure of MS-pyrene. (d) Protocol for
crystal structure simulation by “in silico crystallization”.
[1] H. Takenaka et al., Chem. Mater. 31, (2019) 6696. [2] K. Takimiya, K. Bulgarevich et al., Chin. J. Chem. 40 (2022) 2546-2558.
[3] K. Takimiya, K. Bulgarevich et al., Adv Mater, 33, 32 (2021) e2102914. [4] K. Bulgarevich et al., Chem. Mater. 34, 14 (2022) 6606-6616.

Computational prediction of dynamics and structure of organic semiconductor crystals
Go Watanabe1,21 Kitasato University, 1-15-1 Kitasato Minami-ku, Sagamihara 252-037, Japan,
2 Kanagawa Institute of Industrial Science and Technology, 705-1 Shimoizumi, Ebina 243-0435, Japan
go0325@kitasato-u.ac.jp
Keywords: organic semiconductors, molecular dynamics simulation, crystal structure prediction
Organic semiconductors (OSCs) have attracted much attention because they have a potential to be applied to flexible and printed
electronic devices. In general, when developing a new organic molecule, it requires much time and effort to design and synthesize
the molecule and perform X-ray diffraction analysis of its single crystal. To create new OSCs with innovative functions andphysical properties, it is necessary to establish a novel method utilizing computational science for predicting crystal structure anddynamics of OSCs.
Recently, we reported that thermal fluctuation of each atom and structural stability of organic crystals can be calculated byperforming molecular dynamics (MD) simulations. The organic semiconductors with high carrier mobility showed significantly
larger thermal fluctuations of each atom than those with low carrier mobility (Figure 1). It was also confirmed that the thermal
fluctuations of OSC thin films could be analyzed and the larger fluctuations at the air interface resulted in the destabilization andsurface roughness of self-assembled thin films of OSCs. The MD simulations would make it possible to estimate charge-carrier
mobility.
To predict the crystal structure of a OSC molecule, we propose a new approach that combines molecular mechanics (MM) andmolecular dynamics (MD) calculations. At first, candidate crystal structures from a 3D conformation of a target molecule areprovided by using the software based on MM calculation. Followed by MD simulations for the predicted crystal structures, themost appropriate crystal structure of the molecule can be determined. The new method proposed was confirmed to predict crystal
structure of typical n-type OSCs precisely. Our computational science approach based on molecular simulations would accelerate
to create new innovative OSCs and lead to breakthrough in organic electronics.

Figure 1. Color-coded thermal fluctuations obtained from the trajectories of the bulk single crystals ofPhC2-BQQDI and PDI-FCN2 during the last 10 ns of 100 ns MD runs.

Transient delocalization in organic molecular semiconductors
David Beljonne
Laboratory for Chemistry of Novel Materials
University of Mons, Place du Parc 20, 7000 Mons (BELGIUM)
Keywords: molecular crystals, modelling, surface hopping simulations, charge transport

There is compelling evidence that charge carriers in organic semiconductors (OSs) self-localize in nano-scale
space because of dynamic disorder. Yet, some OSs, in particular recently emerged high-mobility organic
molecular crystals, feature reduced mobility at increasing temperature, a hallmark for delocalized bandtransport. Here we present the temperature-dependent mobility in two record-mobility OSs: DNTT
(dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene), and its alkylated derivative, C8-DNTT-C8. By combining
terahertz photoconductivity measurements with fully atomistic non-adiabatic molecular dynamics simulations,
we show that while both crystals display a power-law decrease of the mobility (µ) with temperature (T,following: µ∝ T^(-n)), the exponent n differs substantially. Modelling provides n values in good agreementwith experiments, and reveals that the differences in the falloff parameter between the two chemically closely
related semiconductors can be traced to the energy-dependent delocalization of the states thermally accessedby the charge carriers, which in turn depends on the specific electronic band structure of the two systems. Theemerging picture is that of holes surfing on a dynamic manifold of vibrationally-dressed extended states witha temperature-dependent mobility that provides a sensitive fingerprint for the underlying density of states.