Photoinduced Aryl Transfer from Imidazolyl-Quinoline π-Conjugated Systems

Abstract

Aryl transfer between heteroatoms was photochemically available through radical initiation followed by a bimolecular reaction. However, such an excited-state reaction has rarely been reported through a photoinduced intramolecular pathway in the π-conjugated systems. Herein, we found, for the first time, a clean photoinduced intramolecular aryl shift for imidazolyl-quinoline derivatives 2NQ (imidazophenanthrene) and 4NQX (imidazophenanthroline), of which the photoproducts are thermally reversible. Upon light irradiation of the studied compounds in solution, an appreciable blue fluorescence along with a gradual change in color appearance was observed, the photoluminescence and photoconversion quantum yields of which were shown to be competitive in the same excited state. We were able to harness the photoconversion quantum yields of the NQ compounds with facile electronic modifications. These, in combination with time-resolved studies on the NQ compounds, gave an oxygen-insensitive aryl transfer rate within 1−100 ns. The anomalously slow intramolecular reaction rates were further proven to be associated with the ∼5.0 kcal/mol transition free energy. The photoproducts NQ_rs were isolated, identified by X-ray analyses, and also shown to demonstrate anti-Vavilov reverse reactions back to the NQ compounds in the higher-lying excited state. The discovery of photoinduced intramolecular aryl transfer paves a new pathway in the synthetic field, which may also be extended and far-reaching to solar−chemical storage under an appropriate design strategy.

Unusual Effects of the Metal Center Coordination Mode on the Photophysical Behavior of the Rhenium(I) and Rhenium(I)–Iridium(III) Complexes

“…The polytopic diimine ligands ( NN1 , NN2 , and NN3 ) were synthesized according to the previously reported general approach (Scheme ) to give conjugated aromatic systems containing diimine-coordinating functions of different (phenanthroline, imidazole-quinoline, and imidazole-pyridine) nature. The NN2 and NN3 ligands contain two diimine functions that allow the preparation of homo- and heterobinuclear complexes described below.…”

“…1-Phenyl-2-(quinolin-2-yl)-1 H -phenanthro­[9,10- d ]­imidazole ( NN1 ), 1-phenyl-2-(quinolin-2-yl)-1 H -imidazo­[4,5- f ]­[1,10]­phenanthroline ( NN2 ), 1-phenyl-2-(pyridin-2-yl)-1 H -imidazo­[4,5- f ]­[1,10]­phenanthroline ( NN3 ), Ir 2 ( NC1 ) 4 Cl 2 , Ir 2 ( NC2 ) 4 Cl 2 , and Ir 2 ( NC4 ) 4 Cl 2 were prepared according to the literature protocols. The syntheses of methyl 2-(2,4-dimethoxyphenyl)­quinoline-4-carboxylate ( NC3 ) and Ir 2 ( NC3 ) 4 Cl 2 are provided in the Supporting Information.…”

Synthesis, structure and luminescence of two europium complexes of diphenylimidazophenanthrolines

“…Imidazo[4,5- f ][1,10]phenanthroline and its derivatives are excellent chelators in coordination chemistry. 2,3 Possessing planar rigid moieties and deficit electron conjugated systems, they can serve as an “antenna” to sensitize the luminescence of the coordinated lanthanide ions. The luminescent properties can be functionally tuned by altering the pending groups to the imidazole moiety, which imparts versatility to these ligands and their complexes.…”