Abstract
In this study an efficient and straightforward method for obtaining a new class of blue fluorescent bezofuran derivatives, under microwave irradiation, as well as under conventional thermal heating, is presented. Under conventional TH the reactions occur selectively, and a single type of benzofuran ester derivative was obtained. The synthesis under MW irradiation also led to benzofuran derivatives, but in a time-dependent manner. Irradiation for a short period of time led to a mixture of two types of benzofuran derivatives (3a–c and 4a–c), while MW irradiation for a longer period of time led to a single type of benzofuran (3-methylbenzofuran), the reaction becoming highly selective. Taking into consideration the advantages offered by MW irradiation in terms of a substantial decrease of solvent consumed, a substantial reduction in reaction time (from days to hours), and a consequent diminution in energy consumption, these methods could be considered environmentally friendly. Here, feasible reaction mechanisms for the benzofuran derivatives formation are described. The absorption and fluorescence emission of the obtained benzofuran derivatives were studied, with part of these compounds being intense blue emitters. A certain influence of the benzofuran substituents concerning absorption and fluorescent properties was observed. Only compounds anchored with a carbomethoxy group of furan ring have shown good quantum yields.
Highlights
The synthesis of highly fluorescent derivatives with extended π-conjugation has been a topic of considerable research because of their potential applications [1,2,3,4,5,6,7,8,9]
In a continuation of our search for new entities with antimicrobial and/or anticancer activity, in previous research works [25,26] we synthesized a series of new azaheterocycle derivatives with a dihydroxyacetophenone skeleton, with the reactions being studied under conventional thermal heating (TH) and under ultrasound (US) or MW irradiation
The first stage of synthesis involved an O-alkylation reaction of DHA and interesting behavior was noticed in the case of DHA with a hydroxyl group at the second position of the benzene ring: a selective bis-O-alkylation took place under conventional TH while under US or MW irradiation a selective mono-O-alkylation took place
Summary
The synthesis of highly fluorescent derivatives with extended π-conjugation has been a topic of considerable research because of their potential applications [1,2,3,4,5,6,7,8,9]. Fused O-heterocyclic rings offer very interesting optical properties. Benzofuran derivatives represent such a class, being a “pure”. In the case of benzofuran derivatives, the literature data shows that they are chromophores with high photoluminescence and good quantum yields [2]. For this reason, benzofuran derivatives have applications in a variety of fields, including sensors and biosensors [5,6], electroluminescent materials [3,4,7], lasers, and other optoelectronic devices. Various other classes of benzofurans are attractive to chemists for their biological activities such as antimicrobial [14], antioxidant [15], anti-inflammatory [16], antifungal [17], PPARD
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