Hydrogen-Bonded Self-Assembly of Supramolecular Donor-Acceptor Complexes of (E)-Bis(18-crown-6)azobenzene with Bis(ammoniopropyl) Derivatives of Bipyridine and Dipyridylethylene in Acetonitrile"статья
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Дата последнего поиска статьи во внешних источниках: 26 июня 2024 г.
Аннотация:The supramolecular complex formation between donor (E)-bis(18-crown-6)azobenzene ((E)-1) and bis(ammoniopropyl) derivatives of bipyridine and dipyridylethylene acceptors (2, (E)-3) was studied in MeCN using steady-state time-resolved fs absorption spectroscopy and quantum-chemical (DFT, TDDFT, QDPT) calculations. The complexes are quite stable but they undergo decomposition via substitution by alkali and alkaline-earth metal cations. A relaxation scheme was proposed for (E)-12 and (E)-1(E)-3 singlet states excited by a 30 fs laser pulse. It involves very fast vibrational relaxation (1 = 88, 60 fs), fast conversion from ππ* to almost indistinguishable nπ* and charge transfer (CT) states (2 = 259, 331 fs), followed by non-radiative deactivation to the ground state (3 = 1.52, 2.48 ps). The formation of 1:1 and 1:2 complexes between (E)-1 and alkali and alkaline-earth metal cations was proposed. Spectral-kinetic parameters and stability constants were calculated. The determined stability constants are generally lower than those for bis(crown)stilbene complexes due to moderate electron-donor ability of azobenzene. The plot of fluorescence quantum yields of 1(Mn+)2 vs charge density of the metal cation shows two separate linear relations for unipositive and dipositive ions. The results of quantum-chemical calculations supported the conclusions derived from time-resolved experiments.