Synthesis of n-(4-(9h-carbazol-9-yl)phenyl)-n-acetylacetamide

Abstract

When talking about luminescent organic materials, in most cases the main attention is paid to materials that have fluorescence, while phosphorescent compounds are given relatively less attention. According to IUPAC, phosphorescence can be represented as a light-emitting transition from a higher energy level to a lower one, and is accompanied by a change in the electron spin, thus in the classical case there is a transition from excited triplet level (T1) to basic singlet (S0) [1]. Today, the phenomenon of phosphorescence has not been studied in as much detail as the phenomenon of fluorescence, hence the design of phosphorescent compounds is an important task. In addition, phosphorescent compounds are often used in OLEDs [2], chemosensors [3] and bioimaging [4]. To date, there are a huge amount of different phosphorescent organic compounds [5–7], but special attention is paid to compounds that contain carbazole in their structure [8, 9], which is often used as a building block for the design of organic phosphorescent compounds. Finally, we decided to choose carbazole for the synthesis of new phosphorescent compounds. In order to obtain the target molecule, we started from reaction of nucleophilic aromatic substitution between 1-fluoro-4-nitrobenzene 1 and carbazol 2 , the resulting compound was reduced to 9-(4-aminophenyl)-9Н-carbazole 4 by using nickel chloride hexahydrate with sodium borohydride in THF/EtOH under mild conditions. Eventually, the according amine 4 , interreacted with acetic anhydride, after purification of resulting mixture by the column chromatography on silica gel using as eluent a mixture of hexane/DCM 2/1 and the following recrystallization from EtOH gave us the terminal N-(4-(9 H -carbazol-9-yl)phenyl)-N-acetylacetamide 5 as a white-yellow crystals. After UV-irradiation (365 nm) of compound 5 we saw the long room temperature phosphorescence. The structure of compound 5 we approve by 13 С and 1 H NMR spectroscopy. Keywords : phosphorescence, cross-coupling, carbazole, nucleophilic aromatic substitution, nickel chloride.