Rational guest selection: a general principle for stabilizing multi-component luminescent materials.

The practical deployment of multi-component luminescent materials is universally hampered by the photodegradation of organic guests, a fundamental challenge that conventional host-centric designs struggle to overcome. Herein, we propose a paradigm-shifting strategy termed "rational guest selection", which elevates the intrinsic molecular photostability of emissive guests to a primary design criterion, equal in importance to emission color. This principle is rigorously validated using the first metal-organic framework constructed from europium ions and pillar[6]arene (Eu-P6MOF) as a model host. While a white-light-emitting composite was initially achieved by co-encapsulating Coumarin 6 and Coumarin 1, its emission color shifted significantly under illumination due to the degradation of Coumarin 1. By applying our principle-rationally replacing the unstable Coumarin 1 with the robust perylene dye-we constructed a stable white-light-emitting composite. The generality of this approach is demonstrated by its success in a low-toxicity ethanol solvent. Mechanistic studies reveal that the rigid MOF pores suppress molecular motions associated with non-radiative decay and photodegradation, with the efficacy of this stabilization being dictated by the guest's innate structural rigidity. The "rational guest selection" principle established here provides a universal blueprint for designing durable multi-component functional materials, transcending specific hosts and applications.