Pyrene fluorophores bearing two carbonyl groups in 1,2- positions: Synthesis and photophysical properties of pyrene-1,2-dicarboximides and a pyrene-1,2-dicarboxamide

• Several fluorescent 7-hydroxy-8,9-dihydro-7H-phenaleno-[1,9-ef]isoindoles and 7H-phenaleno[1,9-ef]isoindole-7,9(8H)-diones were synthesized.
• Their electronic structure and photophysical properties were studied by means of theoretical (TD DFT) calculations and experimental (fluorescence)methods.
• Considerable influence of the carbonyl group at the 2-position on the structure and luminescent properties of these fluorophores was evidenced.

Directed lithiation of pyrene-1-carboxamides, followed by reaction with DMF, afforded 7-hydroxy-8,9-dihydro-7H-phenaleno-[1,9-ef]isoindoles, which were oxidized with Jones reagent to the corresponding pyrene-1,2-dicarboximides. Similarly, the reaction of lithiated N-tert-butylpyrene-1-carboxamide with tert-butyl isocyanate afforded N,N’-di-tert-butylpyrene-1,2-dicarboxamide. The electronic structure and photophysical properties of these compounds were studied by means of theoretical (TD DFT) calculations and experimental (steady-state and time-resolved fluorescence) methods and were compared with those of their pyrene-1- monocarbonyl counterparts. The obtained results reveal the considerable influence of the carbonyl group at the 2-position on the structure and luminescent properties of this class of pyrenyl fluorophores.