title: Observation of intramolecular singlet and triplet excimers of tethered naphthalene moieties under the geometric constraints imposed by the host framework of zeolites.
abstract: This paper describes the emission spectroscopic investigation of singlet and triplet excimers of tethered bisnaphthalene species at room temperature. 1,1'-Dinaphthylethane (DNE) and 1,1'-dinaphthylpropane (DNP) were incorporated into a 3-D network of a 1.3 nm diameter pseudo-spherical supercage of zeolites Y (with an entry aperture of 0.74 nm), and a 1-D channel of zeolite L with a 0.71 nm aperture. In the straight channel of zeolite L, DNP adopts a parallel-sandwich conformation as suggested by the observation of entirely excimeric fluorescence, while DNE can only enter the channel in an open form. As a result, incorporation of DNP into zeolite L exchanged with Tl(+) ions, which induce enhanced intersystem-crossing, allowed the observation of a broad and featureless phosphorescence spectrum that is ascribable to the triplet excimer of DNP. In contrast, an entirely monomeric phosphorescence is observed for DNE. Furthermore, we observed a monomeric phosphorescence spectrum for DNP in Tl(+)-exchanged zeolite Y, in which DNP was shown to assume its open conformation. Thus the parallel-sandwich structure is responsible for the triplet excimer of the bisnaphthalene species as well as for the singlet counterpart. The parallel-sandwich conformation of the triplet excimer of DNP immobilized by the host framework is significantly different from the previously proposed L-shaped configuration in solution. However, it is very similar to that of the triplet excimer of triple-tethered carbazolophane, as revealed quite recently by Ohkita's group (J. Phys. Chem. B, 2007, 111, 10905). Thus the present study helps tackle the long-term issue of triplet excimer through the use of zeolites.
authors.affiliation: Department of Ecosystem Engineering, The University of Tokushima, Tokushima 770-8506, Japan. hashi@eco.tokushima-u.ac.jp
authors.forename: Shuichi
authors.initials: S
authors.lastname: Hashimoto
authors.forename: Minoru
authors.initials: M
authors.lastname: Yamaji
mesh_terms: D008958:Models, Molecular; D008968:Molecular Conformation; D009281:Naphthalenes / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D017641:Zeolites / Q000737:chemistry*
chemical_list: D009281:Naphthalenes; D017641:Zeolites; C031721:naphthalene