Affiliation:
1. Univ Angers, CNRS, MOLTECH-Anjou SFR MATRIX F-49000 Angers France
2. Department of Chemistry University of Kansas 1567 Irving Hill Road Lawrence Kansas 66045 United States of America
3. TetraScience 294 Washington St Boston MA 02108 United States of America
4. Department of Physical Chemistry University of Geneva 30 Quai Ernest Ansermet CH-1211 Geneva Switzerland
5. Aix Marseille Univ, CNRS, Centrale Marseille UAR 1739, FSCM, Chiropole Marseille France
Abstract
AbstractA homologous series of 4,7‐bis(aryl) substituted benzothiadiazole (BTD) compounds, containing the helicenic derivatives bis([4]helicene), bis([5]helicene) and bis([6]helicene), have been prepared upon a double Suzuki coupling between 3,6‐bis(pinacolyl‐borane)‐BTD and the corresponding bromo‐aryl precursors. The single crystal X‐ray structure of the bis([4]helicene) compound shows the existence of both helicities (M) and (P) on the same molecule. All the compounds of the series are highly emissive in solution, with quantum yields of the emission ranging from 50 to 91 %. The enantiopure compounds (M,M) and (P,P) for the BTD‐bis([6]helicene) have been prepared from the corresponding enantiopure 2‐bromo‐[6]helicene precursors. Their chiroptical properties have been investigated in correlation with density functional theory (DFT) calculations, which allowed to confidently assign the absolute configuration of the helicene arms and to characterize the different electronic transitions, including the low energy charge transfer excitation from helicenes to BTD. The enantiomerically pure fluorophores (M,M)‐ and (P,P)‐BTD‐bis([6]helicene), which exist in solution as two main conformers, according to the DFT calculations, show CPL activity in solution, with glum factors of ≈1.7×10−3 at λem=525 nm, and also in the solid state, with glum factors of ≈1.2×10−3 in spite of the strong decrease of the quantum efficiency.