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Dynamic Chemical Devices: Photoinduced Electron Transfer and Its Ion‐Triggered Switching in Nanomechanical Butterfly‐Type Bis(porphyrin)terpyridines
Author(s) -
LinkeSchaetzel Myriam,
Anson Christopher E.,
Powell Annie K.,
Buth Gernot,
Palomares Emilio,
Durrant James D.,
Balaban Teodor Silviu,
Lehn JeanMarie
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500602
Subject(s) - porphyrin , chemistry , crystallography , terpyridine , electron transfer , singlet state , denticity , quantum yield , photochemistry , crystal structure , excited state , metal , fluorescence , atomic physics , physics , organic chemistry , quantum mechanics
A series of butterfly‐type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different “colours”. Stationary and time‐resolved emission studies of the HZn , ZnAu and Zn 2 Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy‐transfer process is seen from the free base to the Zn‐metallated porphyrin. In the U conformation in Zn 2 Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron‐transfer process to the ground state of the Au wing. Furthermore, the binding of (α,ω)‐diamine substrates to the Zn II –porphyrin sites can also influence the conformation of the system. For the Zn 2 Zn construct, single‐crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six‐coordinate, whereby the zinc atom is coordinated by the η 3 ‐terpy ligand as well by monodentate and semi‐chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double‐trigger‐modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy‐ and electron‐transfer processes can be controlled opening a means of improving the on/off ratio in future constructs.