title: Water-soluble [2.2]paracyclophane chromophores with large two-photon action cross sections.
abstract: A series of alpha,omega-donor-substituted distyrylbenzene dimers held together by the [2.2]paracyclophane core were designed, synthesized, and characterized. Different substituents were chosen to modulate the strength of the donor nitrogen groups and to allow the molecules to be either neutral and soluble in nonpolar organic solvents or charged and water-soluble. The specific neutral structures are (in order of decreasing donor strength) 4,7,12,15-tetra[N,N-bis(6' '-chlorohexyl)-4'-aminostyryl]-[2.2]paracyclophane (1N), 4,7,12,15-tetra[(N-(6' '-chlorohexyl)carbazol-3'-yl)vinyl]-[2.2]paracyclophane (2N), and 4,7,12,15-tetra[N,N-bis(4' '-(6' ''-chlorohexyl)phenyl)-4'-aminostyryl]-[2.2]paracyclophane (3N). The charged species are 4,7,12,15-tetra[N,N-bis(6' '-(N,N,N-trimethylammonium)hexyl)-4'-aminostyryl]-[2.2]paracyclophane octaiodide (1C), 4,7,12,15-tetra[(N-(6' '-(N,N,N-trimethylammonium)hexyl)carbazol-3'-yl)vinyl]-[2.2]paracyclophane octaiodide (2C), and 4,7,12,15-tetra[N,N-bis(4' '-(6' ''-(N,N,N-trimethylammonium)hexyl)phenyl)-4'-aminostyryl]-[2.2]paracyclophane octaiodide (3C). Two-photon excitation spectra, measured using the two-photon induced fluorescence technique, show in toluene the following trend for the two-photon cross sections (delta): 3N > 2N > 1N. In water the delta values follow the same order, 3C approximately 2C > 1C, but are smaller (approximately one-third). Significantly, the fluorescence quantum yield (eta) in water decreases much more for 1, relative to 2 and 3. The two-photon action cross sections (deltaeta) of 2C and 3C are 294 GM and 359 GM, respectively. These values are among the highest reported thus far. These results show that, to maximize the deltaeta in this class of chromophores, one needs to fine-tune the magnitude of the charge transfer character of the excited state, to minimize fluorescence quenching in polar media.
authors.affiliation: Mitsubishi Chemical Center for Advanced Materials, Department of Materials, Institute for Polymers and Organic Solids, University of California, Santa Barbara, California 93106, USA.
authors.forename: Han Young
authors.initials: HY
authors.lastname: Woo
authors.forename: Janice W
authors.initials: JW
authors.lastname: Hong
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.forename: Alexander
authors.initials: A
authors.lastname: Mikhailovsky
authors.forename: Dmitry
authors.initials: D
authors.lastname: Korystov
authors.forename: Guillermo C
authors.initials: GC
authors.lastname: Bazan
mesh_terms: D001555:Benzene Derivatives / Q000138:chemical synthesis / Q000737:chemistry; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D036641:Microscopy, Fluorescence, Multiphoton; D011083:Polycyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D012995:Solubility; D014867:Water / Q000737:chemistry
chemical_list: D001555:Benzene Derivatives; D005456:Fluorescent Dyes; D011083:Polycyclic Compounds; D014867:Water