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White-light emitting (WLE) polymers have attracted continuous attention for their promising applications in solid-state lighting, flexible display and related fields. However, achieving dual-emission and pure white-light emission in a single-component polymer is still challenging. In this study, a brominated single-component polymer BrOD-TFB was designed and synthesized, which shows dual-emission and white light emission properties in solution and room-temperature phosphorescence (RTP) in thin films. The dual-emission properties can be tuned by concentration, solvent polarity, and excitation energy. Spectral analyses and theoretical calculations reveal that the origin of the high-energy emission band (HEB) is intramolecular charge transfer (ICT) along the polymer chain, whilst the low-energy emission band (LEB) originates from the excited-state related to the intra-chain and inter-chain C-Br⋯π interactions as demonstrated by the single-crystal structure of the model compound. Appropriate control of the formation and the destruction of the halogen-assisted interactions can initiate white-light emission in the single-component polymer. More interestingly, by dispersing BrOD-TFB (0.1 wt%) in a non-emissive, colorless and transparent polymer, the characteristics of this white-light emission can be fully demonstrated while exhibiting unexpected RTP properties, with photoluminescence quantum efficiency (ΦPL) of up to 23% and CIE coordinates of (0.32, 0.32).

Luminophores usually suffer from luminescent quenching when introduced into a polymer backbone or side chain, which leads to the inefficient luminescence or even no luminescence of the polymer. In this work, alicyclic imide rings were found to be capable of balancing the donor-acceptor properties between the rigid spacer and the aggregation-induced emission-active fluorophore in light-emitting polymers. Along with the nonplanar and rigid emitter, the suppressed intramolecular charge-transfer effect and interchain disturbance can efficiently preserve the luminescence characteristics of the active center, resulting in high solid-state photoluminescence quantum yields of up to 89%. The amorphous polyimides exhibit excellent thermal properties, such as high glass transition temperature (Tg) values (398 °C) and high thermal decomposition temperature (Td) values (538 °C). As far as we know, these luminescent polymer materials are of excellent heat resistance with the highest luminescence efficiency reported. The results have significant impact for the precise prediction of the optical properties of light-emitting polymers by appropriate monomer design, providing controllable ways for synthesizing high thermal stability polymeric materials with efficient fluorescence properties.

To expand the existing application conditions of photochromic polymers and enhance the tolerance of photochromic polymer electronic devices in extreme environments, a diamine monomer DTEDA bearing the diarylethylene (DTE) moiety was synthesized and polymerized with commercially available dihydrides to afford three polyimides (PIs, named DTEODPI, DTE6FPI and DTEHPMPI) through chemical imidization. These PIs realized reversible photo-triggered isomerization both in solution and in film state, with solution photoluminescence “on/off” effects. Semi-aromatic DTEHPMPI showed the largest contrast of color and fastest light response due to its local excited (LE) state. This research provides a simple method to prepare photochromic polymer materials with excellent comprehensive properties.

A series of rigid nonconjugated polyimide (PI)-based thermally activated delayed fluorescence (TADF) polymers were reported for the first time, based on a "TADF-Linker-Host" strategy. Among of which, the TADF unit contains a typical TADF luminous core structure, the "Host" unit exhibits effective conjugation length that endows polyimide with high triplet energy, and the "Linker" unit has an aliphatic ring structure to improve solubility and inhibits intramolecular charge transfer effect. All the TADF polymers exhibit high thermal stability (Tg >308.7 °C) and refractive index (1.76-1.79). Remarkably, highly-efficient polymer light-emitting diodes (PLEDs) based on the polymers are successfully realized, leading to a maximal external quantum efficiency of 21.0 % along with low efficiency roll-off. Such outstanding efficiency is amongst the state-of-the-art performance of nonconjugated PLEDs, confirming the effectiveness of structural design strategy, providing helpful and valuable guidance on the development of highly-efficient fluorescent polymer materials and PLEDs.

To develop stimuli-responsive polymers with highly comprehensive properties, sulfide-containing polyimides with relatively simple structures were designed and synthesized. The polyimides were found to have infrequent oxidation-induced fluorescence turn-on effects by being soaked in hydrogen peroxide (H2O2). The high contrast ratios of fluorescence quantum yield, from not being detected to up to 9.1%, were observed before and after reacting with H2O2. Varied emission wavelengths could be achieved by tailoring the monomer structure. This H2O2-sensitive phenomenon was believed to be the result of the inhibition of charge-transfer effects in the polyimide molecular structure by turning sulfide (donor) into sulfone (acceptor) in the diamine moiety. Furthermore, these tough and thermally stable polyimide films accomplished fluorescence turn-on characteristics without sacrificing their original comprehensive performance of good flexibility and transparency, indicating their potential in high-performance H2O2 sensors, data-security and anti-counterfeit materials.