Obtenção de carbazóis conjugados com potencial emprego como componentes de células solares

Abstract

The energy generation in a broad, sustainable and efficient mode remains a challenge for the modern society. Dye-sensitized solar cells belong to a class of devices involving the conversion of light into electric current from photovoltaic effect by using organic compounds as absorbers. Comparing with some traditional systems, this approach has advantages, such as: lower cost, lightness, flexibility, tuning of charge transport properties, among others. In this context, conjugated systems based on the carbazole scaffold have been promising when used as sensitizers. Considering the importance of organometallic catalysis in the formation of biaryl systems and analogs, the present work aims for the synthesis of 3,6-diarylcarbazoles through Suzuki-Miyaura reactions catalyzed by Pd(0) nanoparticles stabilized by PEG-300. Catalytic reactions were carried out under reflux and microwave irradiation at 95°C (or 130°C in some cases). GCMS analyzes indicated high conversions in detriment of selectivities. Using reflux conditions (2 mol% Pd(0), K2CO3, 90°C and 24h), the products 3,6-diphenyl-9H-carbazole (87) and 3,6-di(naphthalen-1-yl)-9Hcarbazole (93) were obtained in yields of 50.5% and 92%, respectively. Under microwave irradiation and the same reaction conditions - with a reaction time of 2h - the products 3,6- diphenyl-9H- Carbazole (87) and 3,6-di(thiophen-3-yl)-9H-carbazole (90) with obtained in yields of 80.6% and 52.5%, respectively. However, the product 3,6-di(naphthalen-1-yl)-9Hcarbazole (93) showed the lowest yield (47.1%) under these microwave conditions. Analysis of the catalytic system by dynamic light scattering revealed that microwave irradiation conditions lead to an increase in the mean size distribution of PdNPs. It is possible that the low selectivities (or absence) observed for most of the cross-coupling products are related to aspects of base and reagents low solubilities, as well as the partial deactivation of the catalytic system. It should be noted that the products obtained through the Suzuki-Miyaura crosscoupling reactions of this work will be used as sensitizing dyes in solar cells.