Fluorinated Trimers for Enhancing the Stability and Solubility of Organic Small Molecules Without Spectral Shifts: Ultrastable Ultraviolet Absorbers for Transparent Polyimide Films

The development of highly stable organic small molecules for optical applications is of growing interest. Multimerization of monomeric small molecules can enhance stability via increased π-π stacking, but it often reduces solubility and induces undesirable spectral shifts due to π-extension. To overcome this trade-off, we report a trimeric small molecule (F-TPBT) derived from a model monomer (Tinuvin 327) using a 1,3,5-fluorinated phenyl linker. This design markedly improves thermal stability and solubility while minimizing changes in the optical absorption spectrum. F-TPBT shows superior thermal properties (5 wt% decomposition temperature = 427 °C; weight loss after 1 hour at 300 °C = 0.32 wt%) and excellent solubility (5.3 wt% in dichloromethane; 6.4 wt% in N-methylpyrrolidone (NMP)), with an absorption spectrum nearly identical to that of Tinuvin 327. These properties make F-TPBT a promising UV light absorber for transparent polyimide (TPI) films, which require processing above 300 °C and are widely used in flexible displays. Notably, F-TPBT-containing films retain their absorption properties even after 80 hours of accelerated UV irradiation, demonstrating excellent photostability. This study presents a broadly applicable molecular design strategy for enhancing the stability and solubility of organic small molecules while avoiding significant spectral shifts.