Figure 1: Chemical structures of designed phosphor and polymer and description of covalent cross-links strategy.

(a) Chemical structures of the newly designed DA1 and PFMA are shown. Diels–Alder click reaction in DA1-doped PFMA blend film forms covalent bonds between DA1 and PFMA, resulting in greatly enhanced phosphorescence efficiency (ΦP) compared with Br6A-doped PFMA blend film having no covalent linkages. (b) A general Jablonski diagram of organic emitters is presented. General rules for efficient RTP emitters are shown in the grey box. The influence of cross-linking via the Diels–Alder reaction is described in the blue box. The restriction of motions of phosphors and matrices by cross-linking effectively reduces the collision frequency and hence the Dexter-type triplet ET processes (kq) and the vibronic mixing that directs the reduction of the rate of the ISC process from T1 to S0 (kTS).