Introduction of an electron push-pull system yields a planar Red Kaede fluorescence protein chromophore analogue stabilized by a C = O… π interaction

Crystal structures of four red kaede fluorescence protein chromophore analogues are reported here. Molecules I-III adopt a non-planar geometry stabilized by π … π stacking and hydrogen bonding. Introduction of an electron push-pull system induces molecule IV to be planar and a C = O… π supramolecular interaction is observed as well. Strong electron withdrawing and donating groups also ensure formation of a higher order two and three dimensional supramolecular architecture through hydrogen bonds in molecules I and IV. All the analogues exhibit good photoluminescence properties and emit in the red region with excellent quantum yields. Graphical Abstract Crystal structures of four Red Fluorescence Protein ( rfp ) chromophore analogues are reported. Molecules I-III are non planar despite having a linear π-conjugated system. All these three structures are mainly stabilized by π…π interactions, C-H…π and hydrogen bonding. In molecule IV , incorporation of an electron push-pull system introduced a weak C=O…π interaction that made the molecule planar.