Narrow-spectrum and strong-absorptive fluorescent dyes: molecular design strategy and electroluminescence applications

Narrow-spectrum, strong-absorptive fluorescent dyes are effectively meeting the requirements of organic light-emitting diodes (OLEDs) for colour purity and exciton energy utilisation, showing considerable potential for future display applications. As typified by cyanine dyes, the absorption and emission spectral behaviors are strongly correlated with their intrinsic electronic structural features: homogeneous bond lengths and alternating atomic charges. Further studies reveal that these electronic structural features arise from the resonance balance of two ground-state resonance forms, and this balance can be modulated by donor-acceptor substituents. On this basis, this review comprehensively summarizes the molecular design strategies of fluorescent dyes for OLEDs, followed by a systematic overview of their inherent advantages, remaining challenges, and future application prospects in electroluminescent devices.