Colorless Partially Alicyclic Polyimides Based on Tröger’s Base Exhibiting Good Solubility and Dual Fluorescence/Phosphorescence Emission

This study proposes a molecular design and synthetic route to novel colorless, transparent polyimides that exhibit dual fluorescence/phosphorescence emission at long wavelengths applicable to solar energy conversion. Partially alicyclic polyimides (Ac-PI-TBs) based on Tröger’s base (TB) and denoted as Ac-PI-TB-1, Ac-PI-TB-2, and Ac-PI-TB-3 were synthesized by in situ TB formation. The resulting Ac-PI-TBs are readily soluble in common organic solvents and have good mechanical properties with tensile strengths of 72.5–102.3 MPa, elongations at breaks of 12.5–75.0%, low dielectric constants (∼2.66) and low thermal diffusivities (D_⊥ ≤ 7.7 × 10^–8 m²/s), and good thermal stability. The films are totally colorless and transparent with transmittances above 77% at 400 nm. The films also show dual fluorescence and phosphorescence emissions with Stokes shifts as large as 11 421 cm^–1 at low temperatures. The results highlight the possible application of these films in the spectral conversion of unused UV solar radiation to useful visible light.