Abstract
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.
Highlights
The high absorption of light in the visible and near-infrared regime displayed by squaraine dyes has intrigued many research groups in the last 60 years.[1,2,3] The unique photophysical properties arise from the intramolecular charge-transfer between the electron-poor quadratic core and the fused electron-rich arene substituents
After obtaining an amide substituted precursor, condensation with squaric acid was performed using a modification of the original procedure by Sprenger and Ziegenbein.[39]
Synthesis route starting from amide functionalised arenes that are reacted with squaric acid to yield Synthesis of chiral (S-)SQ-1 and a-SQ-1 as green, and SSQ-2 and a-SQ-2 as blue solids
Summary
The high absorption of light in the visible and near-infrared regime displayed by squaraine dyes has intrigued many research groups in the last 60 years.[1,2,3] The unique photophysical properties arise from the intramolecular charge-transfer between the electron-poor quadratic core and the fused electron-rich arene substituents.
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