Stimulus-triggered Anion-Cation-Exciplex Formation in Copper(I)-Complexes as new Mechanism for Mechanochromic Phosphorescence

The investigation of the mechanisms of mechanochromic lumine scenceis of fundamental importance for the development of materialsfor photonic sensors, data storage or luminescence switches. Thestructural origin for this phenomenon in phosphorescent molecular systems is rarely known and thus the formulation of structurepropertyrelationships remains challenging. For d10 coinage metalcompounds, changes of M-M interactions have been proposed asthe main mechanism. Herein, we describe a new mechanism, which is mechanically induced reversible cation-anion exciplex formationbased on Cu-F interactions, that leads to highly efficient mechanochromicphosphorescence and for CuI complexes unusual large emission shift from UV-blue to yellow. The low-energy lumine scence is thermo- and vapo responsive, allowing for the generation of whitelight as well as for recovering the original UV-blue emission.