Synthesis of 3,6,8,11-tetramethyl-5H,9H-quino[3,2,1-de]acridine-5,9-dione

Abstract

The latest progress in the construction of organic light-emitting diodes (OLEDs) has created a demand for the development of new, convenient and efficient methods of synthesis of completely organic phosphors with an elongated π-system and a set of electrochemical and photophysical properties. Nowadays, the last generation of organic emitters for high-performance OLEDs is materials that demonstrate thermally activated delayed fluorescence (TADF) phenomenon. Such materials can convert into light energy, both emitting singlet and dark triplet excitons and, thus, the internal efficiency of OLEDs, based on such compounds, reaches 100 %. Two main approaches have been developed for a targeted synthesis of organic TADF materials. The first and most studied of these is the synthesis of donor-acceptor conjugates, in which the donor and acceptor units are placed relative to each other at a significant angle, close to 90°. The second approach to the molecular design of TADF materials is to construct polynuclear heterocyclic compounds with a rigid framework, in which HOMO and LUMO are localized on the atoms of the cycles through one. The first example of a successful implementation of such strategy was the boro-azo-heterocyclic compound DABNA-1, the synthesis and characterization of which was first published in 2016. It was later discovered that boron acceptor atoms in the design of such compounds can be successfully replaced by carbonyl moieties, and, thus, it can simplify the synthesis and design of such compounds. Therefore, the attention of researchers was attracted by 5 H ,9 H -quino[3,2,1-de]acridine-5,9-dione heterocyclic system. The Ullmann reaction between 3,5-dimethyl-2,6-dicyanoaniline and 4-iodotoluene gave 2- (bis(4-methylphenyl)amino)-4,6-dimethylisophthalonitrile, which was heated in polyphosphoric acid for 4 hours. As a result intramolecular electrophilic cyclization involving both nitrile groups with the formation of 3,6,8,11-tetramethyl-5 H ,9 H -quino[3,2,1-de]acridine-5,9-dione take place. Keywords: 3,5-dimethyl-2,6-dicyanoaniline, 5H,9H-quino[3,2,1-de]acridine-5,9-dione, Ullmann reaction, cyclization, polyphosphoric acid.