title: Self-trapping limited exciton diffusion in a monomeric perylene crystal as revealed by femtosecond transient absorption microscopy.
abstract: Self-trapping and singlet-singlet annihilation of the free excitons in a monomeric (beta) perylene crystal were studied by using femtosecond transient absorption microscopy. The free exciton generated by the photo-excitation of the beta-perylene crystal relaxed to the self-trapped exciton with a rate constant of 7 x 10(10) s(-1). The singlet-singlet annihilation of the free exciton observed under the high excitation density conditions was competed with the self-trapping of the free exciton; we estimated the annihilation rate constant for the free exciton to be 1 x 10(-8) cm(3) s(-1) from the excitation density dependence of the free exciton decay. After self-trapping of the free exciton, no annihilation was observed in the 100 ps time range, suggesting that the diffusion coefficient was reduced drastically by self-trapping. The results show that the major factor limiting the exciton diffusion in the beta-perylene crystal is a relaxation of the free exciton to the self-trapped exciton, and not the lifetime of the exciton. Though the singlet-singlet annihilation rate constants and fluorescence lifetime of the beta-perylene crystal are similar to those of the anthracene crystal, the estimated exciton diffusion length (2 nm) in the beta-perylene crystal is much smaller than that (100 nm) in the anthracene crystal as a result of the exciton self-trapping.
authors.affiliation: National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565, Japan.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Yago
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Tamaki
authors.forename: Akihiro
authors.initials: A
authors.lastname: Furube
authors.forename: Ryuzi
authors.initials: R
authors.lastname: Katoh
mesh_terms: D000873:Anthracenes / Q000737:chemistry; D003460:Crystallization; D008853:Microscopy / Q000295:instrumentation / Q000379:methods; D010569:Perylene / Q000737:chemistry*; D017785:Photons; D013050:Spectrometry, Fluorescence / Q000295:instrumentation
chemical_list: D000873:Anthracenes; D010569:Perylene; C034020:anthracene