Emission behaviours of novel V- and X-shaped fluorophores in response to pH and force stimuli.

A family of novel fluorophores with V- and X-shaped skeletons is rationally designed and prepared. Due to the extended cross π-conjugation in the X-shaped ones, their emission wavelengths in both solution and the solid state exhibit considerable bathochromic shifts compared with those of the V-shaped ones. It is found that a heavy intramolecular charge transfer (ICT) effect is the primary element for the mechanofluorochromic (MFC) response of this family, and an appropriate crystallinity of the sample is also indispensible for it to be MFC-active. Additionally, most fluorophores in this family are responsive to pH stimuli and display diverse and reversible changes of emission features. Interestingly, a V-shaped fluorophore exhibits a unique size-dependent emission behaviour, which makes it a distinctive three-color emitter.