Double helicene possessing B–N dative bonds built on 1,4-dihydropyrrolo[3,2-b]pyrrole core

Just four steps are required to transform 2-nitrobenzaldehyde into centrosymmetric, quadrupolar N,B-doped nanographenes possessing two nitrogen–boron dative bonds. A convergent fragment coupling strategy allowed rapid access to key intermediates bearing the 1,4-dihydropyrrolo[3,2-b]pyrrole core. 2,6-Di-tert-butylpyridine turned out to be the best base for the formation of B←N bonds. This synthetic strategy can be extended to encompass double helicenes possessing two [7]helicene units bearing four five-membered rings. The size of the peripheral arm influences the reaction output: in the case of replacing benzene with dibenzothiophene, the yield decreases from 75% to 16%. Interestingly only two enantiomers and not meso form are formed in the latter case. The obtained double helicene containing 14 fused rings, exhibits green emission characterized by reasonable fluorescence quantum yield reaching 0.38. This dye has average circularly polarized luminescence brightness (BCPL) of about 15 M−1 cm−1. The analysis of the electronic structure of the dyes with quantum chemical methods reveals highly-delocalized excited states with the core of the dye acting as a electron-donating moiety.

European Union's Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement no. 10100780; European Research Council (ARCHIMEDES, 101097337); Polish National Science Centre, Poland (OPUS 2020/37/B/ST4/00017); COMP-HUB and COMP-R initiatives, funded by the “Departments of Excellence” program of the Italian Ministry for University and Research (MIUR, 2018-2022 and MUR, 2023-2027); French Agence Nationale de la Recherche (ANR) under contract ANR-21-CE07-0058-2 (CONDOR); GLiCID Computing Facility (Ligerien Group for Intensive Distributed Computing, 10.60487/glicid, Pays de la Loire, France.