Helicity Control in the Aggregation of Achiral Squaraine Dyes in Solution and Thin Films

Andreas T. Rösch, Qirong Zhu, Jorn Robben, Francesco Tassinari, Stefan C. J. Meskers, Ron Naaman, Anja R. A. Palmans, E. W. Meijer

Published: 4 January 2021


Helicity control: An unexpected outcome of the co-assembly of achiral squaraine dye a-SQ-1 with its chiral counterpart S-SQ-1 is reported. A maximum in optical activity is observed in the supramolecular aggregates of a 3:1 mixture with a-SQ-1 as the major component. Intriguingly, the highest spin-selective electron transport is observed for this mixing ratio as well, illustrating the direct relationship between optical activity and spin-selective electron transport.




Squaraine dyes are well known for their strong absorption in the visible regime. Reports on chiral squaraine dyes are, however, scarce. To address this gap, we here report two novel chiral squaraine dyes and their achiral counterparts. The presented dyes are aggregated in solution and in thin films. A detailed chiroptical study shows that thin films formed by co-assembling the chiral dye with its achiral counterpart exhibit exceptional photophysical properties. The circular dichroism (CD) of the co-assembled structures reaches a maximum when just 25 % of the chiral dye are present in the mixture. The solid structures with the highest relative CD effect are achieved when the chiral dye is used solely as a director, rather than the structural component. The chiroptical data are further supported by selected spin-filtering measurements using mc-AFM. These findings provide a promising platform for investigating the relationship between the dissymmetry of a supramolecular structure and emerging material properties rather than a comparison between a chiral molecular structure and an achiral counterpart.

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