Chiral diketopyrrolo[3,4-c]pyrrole dyes with different substitution symmetry: impact of adamantyl groups on the photo-physical properties in solution and thin films

Here we propose a comparative study on four chiral 1,4-diketo-3,6-dithienylpyrrolo[3,4-c]pyrrole (DPP) dyes with different substitution symmetry on the lactam moieties: (i) symmetrically N-substituted dyes 1-2, bearing two (S)-β-citronellyl (DPP-CT) or (S)-2-methylbutyl (DPP-MT) chains; (ii) non-symmetrically N-substituted dyes 3-4, where an adamantylmethyl appendage replaced one of the (S)-β-citronellyl (DPP-ACT) or (S)-2-methylbutyl (DPP-AMT) chains. The four molecules were synthesized and subjected to detailed investigation of their photo-physical properties in solution (absorbance, fluorescence, cyclic voltammetry) and thin films (absorbance, electronic circular dichroism, optical microscopy), evaluating the impact of different chiral moieties (citronellyl vs. 2-methylbutyl chains) and of different substitution patterns exerted by the adamantane moiety (symmetrical vs. non-symmetrical DPPs). Special emphasis was given to the chiroptical study of thin films, discussing the origin of different supramolecular arrangements in the solid state. Putting together experimental and computational results, we rationalize the chiroptical behavior of these systems in comparison with that of other classes of DPP dyes recently investigated by our group.