Synthesis of novel diketopyrrolopyrrole-based luminophores showing crystallization-induced emission enhancement properties

A series of diketopyrrolopyrrole-based luminophores were synthesized and characterized. Their photoluminescent properties were affected significantly by the change of π-conjugated units and alkyl groups linked to the diketopyrrolopyrrole-ring. 2,5-Dialkyl-3,6-bis(4-((10-oxoanthracen-9(10H)-ylidene)methyl)phenyl)pyrrolo[3,4-c]pyrrole-1,4-dione showed aggregate-induced emission enhancement and crystallization-induced emission enhancement properties while 3,6-bis(4-[1,3]dioxolan-2-yl-phenyl)-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-dione, 2,5-dialkyl-3,6-bis(4-formylphenyl)pyrrolo[3,4-c]pyrrole-1,4-dione, and 2,5-dioctyl-3,6-bis{4-[2-(4-bromophenyl)-2-cyanovinyl]-phenyl}pyrrolo[3,4-c]pyrrole-1,4-dione did not exhibit these properties. The results showed that emission enhancements of the luminophores depended on the competition between the restriction of intramolecular rotation and π–π aggregation with the former causing emission enhancement and the latter inducing fluorescence quenching.

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► The diketopyrrolopyrrole-based luminophores show the aggregate-induced emission enhancement properties.
► The emission enhancement depends on the aggregate-induced restriction of intramolecular rotation and π-π aggregation.
► The former causes the emission enhancement.
► The latter quenches the emission.