Diketone Acceptor Modulation as a Structural Design Strategy for Tunable Carbazole-Cyanostilbene Emitters

A series of carbazole-cyanostilbene luminophores incorporating four diketone-based acceptors (naphthalimide, anthraquinone, phenanthraquinone, and naphthoquinone) were developed to explore the effect of acceptor tuning on emission color and solid-state behavior. Among them, the naphthalimide (NPCZCS), anthraquinone (AQCZCS), and naphthoquinone (NQCZCS) derivatives exhibited distinct solvatochromic shifts, revealing strong charge-transfer characteristics in the excited state, while the phenanthraquinone analogue (PQCZCS) showed nearly solvent-independent emission on varying polarities of solvents due to its localized excited state. Aggregation studies revealed that the naphthalimide and anthraquinone derivatives exhibit a nonclassical AIE behavior, with emission initially increasing upon aggregation and then decreasing at higher fractions, whereas the other two compounds remained nonemissive. In the solid state, the naphthalimide and anthraquinone derivatives displayed bright green (522 nm, ϕ = 24%) and orangish red (610 nm, ϕ = 2.7%) emissions, respectively, accompanied by irreversible mechanofluorochromic responses with clear red shifts upon grinding, as supported by PXRD studies. The high decomposition temperatures (>360 °C) confirmed their excellent thermal robustness. Density functional theory (DFT) and time-dependent DFT analyses supported the experimental findings. Altogether, this study demonstrates how fine-tuning the electronic nature of diketone acceptors in a carbazole-cyanostilbene scaffold can generate color-tunable, thermally stable, and stimuli-responsive materials suitable for next-generation emissive applications.