title: Molecularly Dispersed Donors in Acceptor Molecular Crystals for Photon Upconversion under Low Excitation Intensity.
abstract: For real-world applications of photon upconversion based on the triplet-triplet annihilation (TTA-UC), it is imperative to develop solid-state TTA-UC systems that work effectively under low excitation power comparable to solar irradiance. As an approach in this direction, aromatic crystals showing high triplet diffusivity are expected to serve as a useful platform. However, donor molecules inevitably tend to segregate from the host acceptor crystals, and this inhomogeneity results in the disappointing performance of crystalline state TTA-UC. In this work, a series of cast-film-forming acceptors was developed, which provide both regular acceptor alignment and soft domains of alkyl chains that accommodate donor molecules without segregation. A typical triplet sensitizer, PtIIoctaethylporphyrin (PtOEP), was dispersed in these acceptor crystals without aggregation. As a result, efficient triplet energy transfer from the donor to the acceptor and diffusion of triplet excitons among regularly aligned anthracene chromophores occurred. It resulted in TTA-UC emission at low excitation intensities, comparable to solar irradiance.
authors.affiliation: Department of Chemistry and Biochemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Hosoyamada
authors.affiliation: Department of Chemistry and Biochemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan. yanai@mail.cstm.kyushu-u.ac.jp.|PRESTO, JST, Honcho 4-1-8, Kawaguchi, Saitama, 332-0012, Japan. yanai@mail.cstm.kyushu-u.ac.jp.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Yanai
authors.affiliation: Department of Chemistry and Biochemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan.
authors.forename: Taku
authors.initials: T
authors.lastname: Ogawa
authors.affiliation: Department of Chemistry and Biochemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan. n-kimi@mail.cstm.kyushu-u.ac.jp.
authors.forename: Nobuo
authors.initials: N
authors.lastname: Kimizuka
keywords: crystal phases; photochemistry; photon upconversion; triplet energy migration; triplet-triplet annihilation