Perylene diimide (PDI), initially synthesized and explored as an organic dye, has since gained significant recognition for its outstanding optical and electronic properties. Early research primarily focused on its vibrant coloration; however, the resolution of solubility challenges has revealed its broader potential. PDIs exhibit exceptional optical characteristics, including strong absorption and high fluorescence quantum yield, along with remarkable electronic properties, such as high electron affinity and superior charge carrier mobility. Furthermore, the robust π-π stacking interactions and liquid crystalline behavior of PDIs facilitate precise their self-assembly into highly ordered structures, positioning them as valuable materials for advanced applications in optoelectronics, photonics, and nanotechnology. This article provides a comprehensive review of the progress made in the design, synthesis, and optoelectronic performance of PDI-based liquid crystals. It explores how various substituents and their placement on the PDI core impact the properties of these liquid crystal molecules and discusses the challenges and opportunities that shape this rapidly evolving class of optical materials. This review is strictly focused on PDIs and does not cover their elongated or laterally extended derivatives, nor does it include monoimide or ester compounds.

To reveal the relationships among molecular structures, self-assembly behavior and the organic electronic properties of discotic liquid crystals, 2-(neopentyloxy)-3,6,7,10,11-pentakis(pentyloxy)triphenylene (T5ON1) and 2-pivalate-3,6,7,10,11-penta-pentyloxy-triphenylene (T5EP1) have been synthesized based on hexapentyloxy-triphenylene (HAT5). Their mesomorphic properties were studied by differential scanning calorimetry (DSC), one-dimensional wide-angle X-ray diffraction (1D WAXD) and two-dimensional wide-angle X-ray diffraction (2D WAXD). T5ON1 and T5EP1 showed an ordered hexagonal columnar phase and a highly ordered hexagonal columnar plastic phase, respectively. To our surprise, Transmission Electron Microscope (TEM) images proved that a uniformly distributed superlattice nanostructure formed in the organic system of T5EP1. In addition, the hole and electron mobilities of T5EP1, which were 3.66 × 10⁻² cm² V⁻¹ s⁻¹ and 3.33 × 10⁻² cm² V⁻¹ s⁻¹, respectively, indicated that T5EP1 was a bipolar charge carrier transport material.

The toxicity of lead in conventional perovskites and their inherent chemical instability impede the commercialization of perovskite-based optoelectronics. Therefore, it is vital to develop chemically stable and environmentally friendly Pb-free alternatives. Recently, zero-dimensional (0D) all-inorganic Cs₂ZnCl₄ doped with Sn(II) has emerged as a promising candidate, exhibiting superior chemical robustness, minimal biotoxicity, and exceptional optoelectronic properties. In this work, pressure effects on structure and optical properties in Sn(II)-doped all-inorganic zero-dimensional halide perovskite are investigated both experimentally and theoretically. The structure–property relationship of Sn(II)-doped Cs₂ZnCl₄ is studied using high-pressure techniques. Piezochromism, accompanied by a remarkable change in emission color from orange/red and green to orange/yellow, was obtained from 1 atm to 22.5 GPa. Angle dispersive synchrotron X-ray diffraction (ADXRD) patterns and Raman spectra manifest that the material underwent an isostructural phase transition followed by amorphization with increasing pressure. The piezochromism and band gap engineering originate from the pressure-induced lattice compression and isostructural phase transition. This work advances STE emission studies and provides a robust strategy to boost emission efficiency and to construct multifunctional materials with piezochromism in environmentally friendly perovskites, thus facilitating diverse future applications.