Modification of the Green Fluorescent Protein Chromophore with Large Aromatic Moieties: Photophysical Study and Solid‐State Emission

Green fluorescent protein (GFP)‐like chromophores 1 – 5 , in which the p ‐hydroxylphenyl group is substituted with large aromatic moieties, were synthesized and their crystal structures were determined. Compared with that of p ‐hydroxybenzylideneimidazolinone (GFP chromophore), the fluorescence spectra of 1 – 5 are red‐shifted because of elongated of π‐conjugation. However, the incorporation of large aromatic moieties cannot inhibit the intramolecular torsional motions and, thus, 1 – 5 are generally weakly fluorescent in solution. The results manifest that the solid‐state emission of these GFP‐like chromophores is significantly influenced by the intermolecular packing. The emission spectra of 1 – 5 are further red‐shifted in the solid‐state, and 5 in the crystalline state emits in at red wavelengths with an emission maximum at 624 nm. 1 , 3 , and 4 are weakly emissive in both crystalline and powder forms. Interestingly, one crystalline state of 2 ( 2 B ) emits relatively strongly, whereas another crystalline state 2 A emits rather weakly.