Intramolecular Exciplex Formation Between Pyrene and Tetraazapyrene in Supramolecular Assemblies

Abstract

Tetraazapyrene (TAP), a nitrogen-substituted analogue of pyrene, features a planar and electron-deficient π-conjugation system, and thus can act as a π-electron-acceptor. Despite its unique electronic properties, it remains underexplored due to synthetic challenges and limited derivatization methodologies. Herein, we report the first report of the selective cascade bromination of the TAP core in the presence of dibromoisocyanuric acid, affording 4,9-dibromo-TAP as a key intermediate. This precursor was subsequently employed to construct a novel pyrene-TAP-pyrene trimer (1), in which a central TAP core is flanked by two pyrene units via phosphodiester linkages. Similar to its all-pyrene-based analog in aqueous medium, this trimer undergoes temperature-triggered self-assembly via inter- and intramolecular non-covalent interactions, leading to the formation of supramolecular polymers featured with a donor-acceptor-donor architecture. Upon self-assembly, trimer 1 exhibits distinct optical responses, including enhanced monomeric pyrene fluorescence and unique exciplex emission. These phenomena are attributed to enhanced electronic interactions between pyrene and TAP cores facilitated by their close spatial arrangement in the resulting nanostructures. Our findings demonstrate the reversible and tunable nature of self-assembled nanostructures, highlighting their potential in the development of stimuli-responsive materials.