Synthesis of 1,3‐Dibromopyrene as Precursor of 1‐, 3‐, 6‐, and 8‐Substituted Long‐Axially Symmetric Pyrene Derivatives

Abstract

Pyrene derivatives bearing substituents at positions 1, 3, 6, and 8 find numerous applications, as exemplified by their use in lasers, sensors, and bioimaging probes. However, these derivatives typically have point‐symmetric or short‐axially symmetric structures, whereas long‐axially symmetric derivatives remain underexplored because of the difficulty in obtaining their precursor, 1,3‐dibromopyrene. To address this problem, we herein synthesized 1,3‐dibromopyrene from 1‐methoxypyrene in an overall yield (71% over four steps) considerably exceeding those of existing methods. 1,3‐Dibromopyrene was converted into 13OPA, a long‐axially symmetric pyrene dye with electron‐donor (alkoxy) groups at positions 1 and 3 and electron‐acceptor (formyl) groups at positions 6 and 8. 13OPA exhibited photophysical properties distinct from those of its point‐symmetric and short‐axially symmetric isomers, featuring a broad and strongly redshifted absorption, strong fluorescence with reduced sensitivity to protic solvents, and small dipole moment change upon photoexcitation. The derivatization of 13OPA into a Schiff base and its functionalization via Lewis acid–base pairing were also demonstrated. Thus, our work expands the design scope of pyrene‐based molecules, particularly those used as emitters.