Polyimides with Heavy Halogens Exhibiting Room-Temperature Phosphorescence with Very Large Stokes Shifts

Semiaromatic polyimides (PIs) and imide compounds containing heavy halogens (Br, I) in pyromellitic moieties were designed and synthesized to examine their photoluminescence properties. Solutions of imides and PI films exhibited reddish-color room-temperature phosphorescence (RTP) with very large Stokes shifts (ca. 10000 cm^-1). In addition, the PI films showed small-Stokes-shifted fluorescence emissions at around 540 nm with absorption bands arising from aggregated PI chains at 400-500 nm. Enhanced phosphorescence observed for the PI films under vacuum indicates that the RTP lifetime is significantly influenced by the triplet-triplet energy transfer to atmospheric oxygen. These PIs with very-large-Stokes-shifted RTP are applicable as spectral conversion materials in displays, photovoltaic devices, and crop cultivators, as well as to oxygen/air sensors.