Simultaneously fluorescence-phosphorescence dual-emission based on phenoxathiin and polycyclic aromatic hydrocarbons towards temperature sensing

Abstract

Dual-mode fluorescence-phosphorescence emission materials have attracted significant attention due to their wide range of potential applications. However, it remains challenging to obtain organic dual-mode fluorescence-phosphorescence materials that are both highly efficient and long-lived. To investigate the impact of molecular structure on fluorescent-phosphorescent temperature probes, phenanthrene (Phen) and teriphenylene (TP), two polycyclic aromatic hydrocarbons (PAHs), were introduced into the phenoxathiin (POX) unit, which exhibit a folding-induced enhanced spin-orbit coupling (SOC) effect. The POX derivatives (POXPhen and POXTP) were doped as guest emissive molecules into melamine-formaldehyde (MF) polymer films, showing both highly efficient fluorescence and phosphorescence with phosphorescence quantum yields and lifetimes exceeding 20% and 1 second, respectively. Theoretical and experimental results demonstrate that different steric hindrance effects and van der Waals forces exerted by the Phen and TP groups on the POX unit lead to the perturbed conformations involving the torsion angles between the Phen/TP groups and POX fragments. These perturbed conformations impact the intersystem crossing process and fluorescence and phosphorescence processes. Notably, the molecular conformational distribution exhibits temperature reliability, and the temperature-dependent emission of POXPhen and POXTP demonstrates a good linear response relationship between the phosphorescence to fluorescence intensity ratio (I_P/I_F) and temperature (T), ranging from 9.25 °C to 110.95 °C and 5.25 °C to 88.95 °C, respectively. These findings provide important theoretical guidance for the design of precise temperature probes gauging fluorescent-phosphorescent ratio by regulating the perturbed molecular conformations.