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Symmetrical or non-symmetrical luminescent turnstiles based on hydroquinone stators and rotors bearing pyridyl or p-dimethyaminopyridyl coordinating units

Abstract

The design and synthesis of a novel family of molecular turnstiles T1-T5 were achieved. All five turnstiles are based on a stator and a rotor covalently interconnected. Whereas turnstiles T1-T2 are based on a symmetric stator equipped with two coordinating pyridyl units and a rotor bearing either a pyridyl or p-dimethylaminopyridyl coordinating moiety, the two non-symmetric turnstiles T4 and T5 are based on a stator bearing only a single pyridyl unit and the same rotor as T1 and T2 mentioned above. The switching between the open (T1-T5) and the closed (T-M) states of the turnstiles by metal cations (M = Ag+ or Pd2+) was investigated in solution by 1D and 2D NMR techniques. The locking of the rotational movement leading the closed state of the turnstile was achieved upon addition of Ag+ cation through its simultaneous binding by both pyridyl moieties of the stator and to the rotor. The unlocking process leading back to the open state was achieved by addition of Et4NBr leading to the precipitation of AgBr. For the symmetric turnstiles T1 and T2, bearing two pyridyl units on the stator, the binding of Ag+ cation leads to an oscillating phenomenon between two energetically equivalent closed states. However, in the case of the turnstile T1, the oscillating process could be prevented by blocking the rotational movement using PdCl2 as the locking agent. Owing to the emissive nature of the stator, the open and closed states of the turnstiles were investigated by steady state and time-resolved photophysical methods. The photo-excitation of the turnstiles in their open state leads to an intense near-UV to deep-blue emission with short-lived excited states and a 1ILCT character. Upon binding of Ag+ cation, sizeable bathochromic shifts and substantial decrease of PLQY was observed. Finally, coordination of PdCl2, which possesses lower-lying excited states with MC and LMCT character, completely quenches the photoluminescence.

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Publication details

The article was received on 28 Jul 2017, accepted on 29 Sep 2017 and first published on 29 Sep 2017


Article type: Paper
DOI: 10.1039/C7DT02762A
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Symmetrical or non-symmetrical luminescent turnstiles based on hydroquinone stators and rotors bearing pyridyl or p-dimethyaminopyridyl coordinating units

    B. Godde, A. Jouaiti, A. Fluck, N. Kyritsakas, M. Mauro and M. W. Hosseini, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT02762A

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