Two tetraphenylethene-pyrene isomers: Distinct fluorescence and mechanochromic properties

Melding aggregation induced emission (AIE) scaffolds with aggregation caused emission quenching (ACQ) luminophores might eliminate the ACQ effect and endow such derived molecules with AIE properties and other novel optical behavior. How the AIE scaffold connects with the ACQ luminophore is critical to determine the properties of the resultant molecules. Melding the tetraphenylethene (TPE) building block with pyrene, isomers 1 and 2 were obtained with an ester group connected in different orientations. Molecule 1 with pyrene connecting with the carbonyl of the ester group possessed aggregation induced emission enhancement (AIEE) and three-state mechanochromic behavior, while molecule 2 with pyrene connecting with the oxygen atom of the ester group still exhibited ACQ property. Theoretical calculations revealed that the connection manner with ester group impacted the charge distribution and molecular conformation of these two isomers, thus resulting in their different fluorescence properties in solution and aggregate states. Mechanochromic molecule 1 with three fluorescence states (blue, lambda(em) = 456 nm, Phi(fl) = 5.5%; green, lambda(em) = 504 nm, Phi(fl) = 3.3%; dim, lambda(em) = 461 nm, Phi(fl) = 0.9%) may be promising in the application of optical recording.

Automated summary

Combining AIE scaffolds with ACQ luminophores can eliminate the ACQ effect and give derived molecules new optical behavior. The manner in which the AIE scaffold connects with the ACQ luminophore determines the properties of the resulting molecules. Differences in the connection of pyrene with the ester group led to distinct fluorescence properties in molecules 1 and 2, with molecule 1 showing potential for optical recording applications.