Exciplex Fluorescence as a Diagnostic Probe of Structure in Coordination Polymers of Zn²⁺ and 4,4‘-Bipyridine Containing Intercalated Pyrene and Enclathrated Aromatic Solvent Guests

Abstract

Coordination polymers based on Zn(II)-4,4'-bipyridine (Zn-bipy) frameworks containing pyrene intercalated between adjacent layers and aromatic solvent molecules enclathrated within the framework cavities have been prepared and characterized for the first time. These compounds are highly fluorescent, and show broad, featureless emission spectra significantly red-shifted relative to pyrene monomer fluorescence; this has been assigned to pyrene-bipy exciplex emission. Single-crystal X-ray structural analysis shows that the presence of the aromatic solvent molecule within the cavities has a profound effect on the architecture of these frameworks: in the case of benzene, toluene, p-xylene, and chlorobenzene, the Zn-bipy framework consists of 1-D ladders, whereas in the case of o-dichlorobenzene (the largest solvent guest), the framework was based on a 2-D square grid. This difference in stoichiometry and architecture was also reflected in significant differences in the fluorescence of these coordination polymers, with three of the four compounds with 1-D ladder geometries having similar fluorescence maxima (ca. 520 nm) and lifetimes (ca. 70 ns), whereas the compound with square grid topology had a significantly blue-shifted maximum (ca. 460 nm) and shorter lifetime (ca. 42 ns). It is proposed that exciplexes form upon excitation of ground-state complexes, involving face-to-face bipy/pyrene complexes (pi-pi stacking interactions) in the case of the 1-D ladder structures, but edge-to-face bipy/pyrene and pyrene/o-dichlorobenzene complexes (C-H...pi interactions) in the case of the 2-D square grid structure.

Spin state switching in iron coordination compounds

“…Porous coordination polymers (PCPs), also known as MOFs, represent a new class of functional molecular materials [400–407], which are able to mimic and even improve the functions of zeolites [408], i.e., storage [409–410], separation [411–412], sensing [413] and catalysis [414–416]. The vast majority of their applications are related to pore sizes, shapes, flexibility and structures/environments.…”

Isostructural Metal–Anion Radical Coordination Polymers with Tunable Phosphorescent Colors (Deep Blue, Blue, Yellow, and White) Induced by Terminal Anions and Metal Cations

“…[8][9][10][11][12][13][14][15] In particular, luminescent coordination polymers have flourished because of their utilities as LEDs, chemosensors, sensors, probes, and so on. [16][17][18][19][20][21][22][23] Also, many coordination polymers exhibit tunable luminescent properties induced by ion exchange, guest molecules, or guest ions. [24][25][26][27][28][29][30][31][32] However, studies on direct white-light coordination polymers are still very scarce.…”

Solvothermal syntheses and structures of indium(III)-binaphthalenyl dicarboxylate complexes with yellow/blue luminescence

“…For example, in order to construct complexes with remarkable photoluminescent properties, aromatic organic ligands and d 10 metal ions deserve the researchers' intensive investigation. Aromatic organic ligands may display photoluminescence in the solid state [14][15][16][17][18], while the incorporation of d 10 metal ions is found to be useful to enhance the luminescence intensity and lifetime of their hybrid complexes [19][20][21].…”