Abstract
We report a study of photoluminescent properties of 4-bromo-7-(3-pyridylamino)-2,1,3-benzothiadiazole (Py-btd) and its novel Lewis adducts: (PyH-btd)2(ZnCl4) and [Cu2Cl2(Py-btd)2{PPO}2]·2C7H8 (PPO = tetraphenyldiphosphine monoxide), whose crystal structure was determined by X-ray diffraction analysis. Py-btd exhibits a lifetime of 9 microseconds indicating its phosphorescent nature, which is rare for purely organic compounds. This phenomenon arises from the heavy atom effect: the presence of a bromine atom in Py-btd promotes mixing of the singlet and triplet states to allow efficient singlet-to-triplet intersystem crossing. The Lewis adducts also feature a microsecond lifetime while emitting in a higher energy range than free Py-btd, which opens up the possibility to color-tune luminescence of benzothiadiazole derivatives.
Highlights
Long Lifetime of the Excited State of Chalcogen–nitrogen heterocycles are actively studied owing to the prospects for their application in electronics [1,2] and biomedicine [3]. 2,1,3-benzothiadiazole is a common building block for such applications, featuring electron-withdrawing properties [4,5]
Variation of Lewis acids bound with the pyridyl substituent of Py-btd would change the electronic structure of the molecule and secondary bonding interactions pattern in the crystal and, would result in different luminescent properties of a compound
The target compound 2 in 60% yield was prepared by adding hydrochloric acid to the reaction mixture in chloroform
Summary
Long Lifetime of the Excited State of Chalcogen–nitrogen heterocycles are actively studied owing to the prospects for their application in electronics [1,2] and biomedicine [3]. 2,1,3-benzothiadiazole (btd) is a common building block for such applications, featuring electron-withdrawing properties [4,5].Functionalization of btd with donor substituents provides a way to create luminescent compounds, whose emission occurs owing to the push–pull effect [6,7,8]. 4-bromo-7-(3-pyridylamino)-2,1,3-benzothiadiazole (Py-btd, 1), described recently [19], has a nitrogen atom in the pyridyl substituent, which is known to be a strong Lewis base center. This compound possesses mechanochromic luminescence in solid state, owing to the presence of hydrogen bonds between the amino group and the pyridyl, shortened S···N contacts and “head-to-tail” π–π interactions between benzothiadiazole units. Variation of Lewis acids bound with the pyridyl substituent of Py-btd would change the electronic structure of the molecule and secondary bonding interactions pattern in the crystal and, would result in different luminescent properties of a compound. A number of Zn and Ag coordination compounds with
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