title: Gigantic two-photon absorption cross sections and strong two-photon excited fluorescence in pyrene core dendrimers with fluorene/carbazole as dendrons and acetylene as linkages.
abstract: We report a series of stiff dendrimers (referred to as T1, T2, T3, and T4) that have both gigantic two-photon absorption (TPA) cross sections up to 25,000 GM and strong two-photon excited fluorescence (TPEF) with fluorescence quantum yield of ∼0.5. The large TPA cross sections and high quantum yields of these dendrimers are directly related to their geometrical structures, where the polycyclic aromatic pyrene is chosen as the chromophoric core because of its planar and highly π-conjugated structure, fluorene moieties as dendrons extend the conjugation length through the planar structure, and carbazole moieties are modified at three-, six-, and nine-positions as electron donor. All of these groups are linked with acetylene linkage for effective π-electron delocalization, leading to large TPA cross section and high fluorescence quantum yield. The spectral properties of all dendrimers are investigated by one- and two-photon excitations. Furthermore, steady-state fluorescence excitation anisotropy and quantum chemical calculation are also employed to determine the structure-related mechanism of these dendrimers with gigantic TPA cross sections and high TPEF efficiency. We then show that the improvement of branched chains in the T-series dendrimers enhances the light-harvesting ability. The core emission spectra, fluorescence quantum yield, and fluorescence lifetime are almost invariable by directly exciting the dendrons. These results will provide a guideline for the design of useful two-photon materials with structural motifs that can enhance the TPA cross-section and fluorescence quantum yield of a molecule without causing a red shift of the one- and two-photon excitation wavelengths for specific applications.
authors.affiliation: The State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wan
authors.forename: Linyin
authors.initials: L
authors.lastname: Yan
authors.forename: Zujin
authors.initials: Z
authors.lastname: Zhao
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Ma
authors.forename: Qianjin
authors.initials: Q
authors.lastname: Guo
authors.forename: Mingli
authors.initials: M
authors.lastname: Jia
authors.forename: Ping
authors.initials: P
authors.lastname: Lu
authors.forename: Gabriel
authors.initials: G
authors.lastname: Ramos-Ortiz
authors.forename: José Luis
authors.initials: JL
authors.lastname: Maldonado
authors.forename: Mario
authors.initials: M
authors.lastname: Rodríguez
authors.forename: Andong
authors.initials: A
authors.lastname: Xia
mesh_terms: D000042:Absorption; D000114:Acetylene / Q000737:chemistry*; D050091:Dendrimers / Q000737:chemistry*; D005449:Fluorenes / Q000737:chemistry*; D015394:Molecular Structure; D053758:Nanoparticles / Q000737:chemistry; D010316:Particle Size; D010777:Photochemistry; D017785:Photons; D011721:Pyrenes / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D050091:Dendrimers; D005449:Fluorenes; D011721:Pyrenes; D000114:Acetylene