Synthesis, Structural, and Photophysical Properties of the First Member of the Class of Pyrene‐Based [4]Helicenes

Abstract

Abstract A convenient route to a new class of pyrene‐based [4]helicenes is presented. Wittig reaction of 7‐ tert ‐butyl‐1,3‐dimethyl‐5‐formylpyrene with benzyltriphenylphosphonium salts in the presence of n BuLi afforded 7‐ tert ‐butyl‐1,3‐dimethyl‐5‐(phenylethenyl)pyrenes, from which 4,5‐naphthalene annulated aromatic [4]helicenes, namely 7‐ tert ‐butyl‐1,3‐dimethyl‐13‐methoxydibenzo[ ij , no ]tetraphene and 7‐ tert ‐butyl‐1,3,12,14‐tetramethyldibenzo[ ij , no ]tetraphene, were obtained by photoinduced intramolecular cyclization. The chemical structures of these [4]helicenes were determined on the basis of their elemental analyses and spectroscopic data. The helicity in the synthesized [4]helicene induced by the presence of the second methyl group in the fjord region is discussed in detail. The photophysical and electrochemical properties of these newly developed [4]helicenes were fully investigated by UV/Vis absorption and photoluminescence spectrphotometry, and cyclic voltammetry (CV), and the crystal structures were determined for two examples.