Cyano-functionalized 1,4-bis((E)-2-(1H-indol-3-yl)vinyl)benzenes with aggregation induced emission characteristic and diverse thermochromic behaviour

• A series of cyano-functionalized 1,4-bis((E)-2-(1H-indol-3-yl)vinyl)benzene derivatives have been designed and synthesized.
• All the luminophores displayed TICT and AIE induced fluorescence variations.
• Chain length-dependent thermochromic behaviour were observed for the constructed luminophores.
• The luminophore with hexadecyl groups extraordinarily displayed three-colour emissions.

Five cyano-functionalized 1,4-bis((E)-2-(1H-indol-3-yl)vinyl)benzene derivatives with a donor-acceptor-acceptor-donor structure have been designed and synthesized. All the luminophores exhibit both twisted intramolecular charge transfer and aggregation induced emission characteristics. Meanwhile, significant fluorescence changes (up to 74–77 nm) were observed during their tandem photoluminescence experiments in cyclohexane/THF and THF/water systems. Most importantly, the constructed dyes present chain length-dependent thermochromic behaviour: (1) almost no thermochromism is observed for the three luminophores with relatively short alkyl chains; (2) as for the luminophore with N-tetradecyl groups, it initially exhibits greenish-yellow fluorescence which turns to orange upon heating and the orange emission is retained after cooling; (3) the luminophore with N-hexadecyl groups extraordinarily displays three-colour emissions including greenish-yellow, orange and salmon pink fluorescence in initial, heated and cooled states, respectively. Additionally, the three luminophores with poor thermochromic performance show optical waveguide properties, demonstrated by their fluorescence microscopy images.

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