Improved crystallinity of the asymmetrical diketopyrrolopyrrole derivatives by the adamantane substitution

Alkylation of diketopyrrolopyrroles (DPPs) is a powerful tool for increasing the solubility and processability of these pigments. Moreover, alkylation contributes to solid state packing and structural ordering of DPPs. In this study, the influence of the alkylation and solubilization side group engineering to DPPs on the thermal and optical properties was systematically investigated. Two series (each containing 3 derivatives: N,N'-, N,O′- and O,O′-substituted examples) of alkylated DPPs by 2-ethylhexyl and ethyladamantyl substituents were synthesized. Separation of all formed DPP derivatives was accomplished in order to perform an in-depth study of their physicochemical properties. DSC measurements revealed that the O-substitution caused a decrease in the thermal stability of DPP derivatives. On the contrary, an ethyladamantyl side chain, as a rigid alicyclic substituent, contributed very effectively to the increase of the melting point and thermal stability. The new results provide insights into the development of DPP-alkylated regioisomers and their thermal and optical properties.