title: Large reverse saturable absorption under weak continuous incoherent light.
abstract: In materials showing reverse saturable absorption (RSA), the optical absorbance increases as the power of the light incident on them increases. To date, RSA has only been observed when very intense light sources, such as short-pulse lasers, are used. Here, we show that hydroxyl steroidal matrices embedding properly designed aromatic molecules as acceptors and transition-metal complexes as donors exhibit high RSA on exposure to weak incoherent light at room temperature and in air. Accumulation by photosensitization of long-lived room-temperature triplet excitons in acceptors with a large triplet-triplet absorption coefficient allows a nonlinear increase in absorbance also under low-power irradiation conditions. As a consequence, continuous exposure to weak light significantly decreases the transmittance of thin films fabricated with these compounds. These optical limiting properties may be used to protect eyes and light sensors from exposure to intense radiation generated by incoherent sources and for other light-absorption applications that have not been realized with conventional RSA materials.
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan.
authors.forename: Shuzo
authors.initials: S
authors.lastname: Hirata
authors.affiliation: Department of Organic and Polymer Materials Chemistry, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
authors.forename: Kenro
authors.initials: K
authors.lastname: Totani
authors.affiliation: School of Computer Science, Tokyo University of Technology, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamashita
authors.affiliation: Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Chihaya
authors.initials: C
authors.lastname: Adachi
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan.
authors.forename: Martin
authors.initials: M
authors.lastname: Vacha
mesh_terms: D000042:Absorption; D004958:Estradiol / Q000737:chemistry / Q000528:radiation effects; D007834:Lasers; D008027:Light; D055620:Optical Phenomena; D055668:Photochemical Processes; D013256:Steroids / Q000737:chemistry* / Q000528:radiation effects*
chemical_list: D013256:Steroids; D004958:Estradiol