title: Broadband Two-Photon Absorption Characteristics of Highly Photostable Fluorenyl-Dicyanoethylenylated [60]Fullerene Dyads.
abstract: We synthesized four C60-(light-harvesting antenna) dyads C60 (>CPAF-Cn) (n = 4, 9, 12, or 18) 1-Cn for the investigation of their broadband nonlinear absorption effect. Since we have previously demonstrated their high function as two-photon absorption (2PA) materials at 1000 nm, a different 2PA wavelength of 780 nm was applied in the study. The combined data taken at two different wavelength ranges substantiated the broadband characteristics of 1-Cn. We proposed that the observed broadband absorptions may be attributed by a partial π-conjugation between the C60 > cage and CPAF-Cn moieties, via endinitrile tautomeric resonance, giving a resonance state with enhanced molecular conjugation. This transient state could increase its 2PA and excited-state absorption at 800 nm. In addition, a trend of concentration-dependent 2PA cross-section (σ₂ ) and excited-state absorption magnitude was detected showing a higher σ value at a lower concentration that was correlated to increasing molecular separation with less aggregation for dyads C60(>CPAF-C18) and C60(>CPAF-C₉), as better 2PA and excited-state absorbers.
authors.affiliation: Department of Chemistry, Institute of Nanoscience and Engineering Technology, University of Massachusetts Lowell, Lowell, MA 01854, USA. baschem@hotmail.com.
authors.forename: Seaho
authors.initials: S
authors.lastname: Jeon
authors.affiliation: Department of Chemistry, Institute of Nanoscience and Engineering Technology, University of Massachusetts Lowell, Lowell, MA 01854, USA. wangmin81@gmail.com.
authors.forename: Min
authors.initials: M
authors.lastname: Wang
authors.affiliation: Department of Physics, National University of Singapore, Singapore 117542, Singapore. phyjiwei@nus.edu.sg.
authors.forename: Wei
authors.initials: W
authors.lastname: Ji
authors.affiliation: Functional Materials Division, AFRL/RXA, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, OH 45433, USA. loon.tan@us.af.mil.
authors.forename: Loon-Seng
authors.initials: LS
authors.lastname: Tan
authors.affiliation: Functional Materials Division, AFRL/RXA, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, OH 45433, USA. thomas.cooper.13@us.af.mil.
authors.forename: Thomas
authors.initials: T
authors.lastname: Cooper
authors.affiliation: Department of Chemistry, Institute of Nanoscience and Engineering Technology, University of Massachusetts Lowell, Lowell, MA 01854, USA. Long_Chiang@uml.edu.
authors.forename: Long Y
authors.initials: LY
authors.lastname: Chiang
mesh_terms: D003460:Crystallization; D005449:Fluorenes / Q000737:chemistry*; D037741:Fullerenes / Q000737:chemistry*; D008027:Light; D017785:Photons; D014227:Triazines / Q000737:chemistry*
chemical_list: D005449:Fluorenes; D037741:Fullerenes; D014227:Triazines; C041509:fluorene
keywords: C60-(light-harvesting antenna) nanostructures; Z-scan measurements; nonlinear absorption; ultrafast two-photon absorption