Tetraphenylethylene-Based Wholly Aromatic Polyimides with Enhanced Photoluminescence Efficiency.

Wholly aromatic polyimides (PIs) are promising candidates for next-generation optoelectronic materials owing to their excellent comprehensive properties. However, the strong charge-transfer (CT) interactions present in both solution and solid states typically result in poor photoluminescence (PL) efficiency, posing a significant limitation for conventional wholly aromatic PIs for optoelectronic applications. Tetraphenylethylene (TPE), a well-established fluorophore, is well known for its straightforward synthesis, versatile functionalization capability, and high fluorescence quantum yield (Φ PL) even when decorated with various substituents. Thus, incorporating TPE fluorophore into the PI backbone presents a promising strategy to develop photoluminescent PIs and overcome the inherent drawbacks of traditional conjugated polymers. Herein, TPE-diamines with trans- and cis-configurations were synthesized and subsequently polymerized with 6FDA or BPADA dianhydrides to introduce TPE into the PI main chains (MC-TPE-PIs). However, the resulting MC-TPE-PIs exhibited negligible Φ PL, failing to deliver the anticipated emission properties. To address this limitation, a carboxyl-functionalized TPE derivative (TPE-COOH) was prepared and grafted as a side-chain substituent onto the PI backbone via esterification (SC-TPE-PIs). By tuning the flexibility and electronic effects of the dianhydrides, a series of SC-TPE-PI thin films with varying TPE contents were obtained. Among them, the highest Φ PL reached 13.7%, with a tensile strength of 83.3 MPa, a tensile modulus of 1.78 GPa, a glass transition temperature of 203.1 °C, and a thermal decomposition temperature of 377 °C at 5% weight loss, demonstrating their potential as luminescent polymers for optoelectronic applications.