Full-colour solvatochromic fluorescence emitted from a semi-aromatic imide compound based on ESIPT and anion formation

A multi-colour solvatochromic fluorophore was developed by substituting a fully organic 3-amino-N-cyclohexyl phthalimide group with a p-toluenesulfonyl (tosyl) group. This compound is essentially colourless in the visible region and exhibits reddish fluorescence through excited-state intramolecular proton transfer (ESIPT) in the crystalline state with a considerably large Stokes shift of 9786 cm(-1), as well as bright fluorescence in the full-colour range, from purple to red, when dissolved in 10 different organic solvents. Excitation wavelength measurements, lifetime measurements, and time-dependent density functional theory (TD-DFT) calculations clarified that the full-colour solvatochromism of the fluorescence results from the combination of the fluorescence emissions from the three different excited states: locally excited (N*), intramolecular proton-transferred (T*), and anion states (A*). This unique solvatochromic fluorescence property is expected to be applied in organic electronic devices and biological imaging tools.

Automated summary

A multi-colour solvatochromic fluorophore was developed, showing bright fluorescence in a full-colour range in different organic solvents and having potential applications in organic electronic devices and biological imaging tools.