The origin of the thermally stable white-light emission property of POSS-conjugated polymer hybrid films

We have previously reported thermally stable white-light luminescence from polymer hybrid films consisting of tetraphenylethene (TPE)-tethered polyhedral oligomeric silsesquioxane (POSS) and poly(1,4-phenylenevinylene) (PPV). We observed that the intensity ratios between the dual emission bands from the POSS and the conjugated polymer, and thus the color balance, were maintained even in the higher-temperature region. In this paper, the origin of the thermally stable dual-emission properties of these white-light-emitting hybrid films is investigated using a series of POSS derivatives with different tethered luminophores and various conjugated polymer matrices. We obtained homogeneous hybrid films and revealed that one of the key factors for the expression of dual-emission properties is the relationship between the photoluminescence quantum yields of the energy donors (fillers) (Φ_D) and acceptors (polymers) (Φ_A). When the emission quantum yield of either the donor or acceptor molecules is high, only an emission band originating from the molecule with the higher emission quantum yield can be observed. Dual emission from both the donor and acceptor is detectable only when the Φ_D is as high as the Φ_A or slightly higher than the Φ_A. Based on these findings, we have demonstrated a logical design for dual-emissive materials. We also found that the affinity between POSS and polymers is responsible for maintaining the emission color balance at high temperatures. It was observed that POSS substituted with bulky groups can hybridize with conjugated polymer chains, and that the thermal behavior of the polymer is dominated by the POSS. As a result, the thermal stability can be enhanced. We revealed the origin of the thermally stable white-light luminesce properties of POSS hybrids based on two aspects.