Prompt and Thermally Activated Delayed Fluorescence of Quinazoline-Based Derivatives: A Joint Experimental and Theoretical Study

Abstract

During the last decade, thermally activated delayed fluorescence has been the topic of intense research due to its great potential for highly efficient all organic light emitting devices. While the quinazoline heterocycle has been used for its electron withdrawing ability in various push-pull dyes, quinazoline derivatives have been rarely considered for TADF emitters. Here we design and synthesize a new series of dyes with phenyl- or methoxy-substituted quinazoline rings combined with 9,9-dimethylacridan, phenoxazine or phenothiazine and either 1,4-phenylene or 2,5-thienylene as linker. Combining optical spectroscopy and theoretical investigations, we demonstrate that delayed fluorescence is observed in the solid state for the phenyl-substituted quinazoline derivatives for which both quasi-equatorial and quasi-axial conformations are predicted to coexist. Calculations further suggest that the reversed intersystem crossing is likely to involve the second triplet state that shows small energy splitting with the first singlet state. These results prompt further investigations of phenyl-substituted quinazoline based dyes for TADF.