Room-Temperature Pentacene Fluids: Oligoethylene Glycol Substituent-Controlled Morphologies and Singlet Fission

Keisuke Yoshino; Hayato Sakai; Yoshiaki Shoji; Takashi Kajitani; Hayato Anetai; Tomoyuki Akutagawa; Takanori Fukushima; Nikolai V Tkachenko; Taku Hasobe

doi:10.1021/acs.jpcb.0c09754

Room-Temperature Pentacene Fluids: Oligoethylene Glycol Substituent-Controlled Morphologies and Singlet Fission

J Phys Chem B. 2020 Dec 31;124(52):11910-11918. doi: 10.1021/acs.jpcb.0c09754. Epub 2020 Dec 18.

Authors

Keisuke Yoshino¹, Hayato Sakai¹, Yoshiaki Shoji^{2

3}, Takashi Kajitani^{3

4}, Hayato Anetai⁵, Tomoyuki Akutagawa^{5

6}, Takanori Fukushima², Nikolai V Tkachenko⁷, Taku Hasobe¹

Affiliations

¹ Department of Chemistry, Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan.
² Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
³ RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan.
⁴ Materials Analysis Division, Open Facility Center, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
⁵ Graduate School of Engineering, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.
⁶ Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.
⁷ Chemistry and Advanced Materials Group, Faculty of Engineering and Natural Sciences, Tampere University, Korkeakoulunkatu 8, Tampere FI33720, Finland.

PMID: 33336576
DOI: 10.1021/acs.jpcb.0c09754

Abstract

We report the first synthesis of solvent-free pentacene fluids at room temperature together with observation of singlet fission (SF). Three pentacenes with different number of ethylene glycol (EG) side chains (n) were employed (denoted as (EG)_n-Pc-(EG)_n: n = 2, 3, and 4). The morphologies of these pentacenes largely depend on the lengths of EG chains (n). (EG)₃-Pc-(EG)₃ and (EG)₄-Pc-(EG)₄ indicate fluid compounds at room temperature, whereas (EG)₂-Pc-(EG)₂ is a solid compound. Microscopic clustering with short-range interactions between pentacene chromophores was confirmed in X-ray diffraction profiles of solvent-free fluids. Such a structural trend is an important origin of SF and consistent with the steady-state spectroscopic results. To one's surprise, femtosecond transient absorption spectroscopy demonstrated that SF occurred in thin films prepared from solvent-free fluids of (EG)₃-Pc-(EG)₃ and (EG)₄-Pc-(EG)₄ in spite of such excessive EG chains.