Ketone-Driven Solid-State Emission Color Modulation from Cyan to Red in Carbazole–Cyanostilbene-Based A–D–A Luminophores

We report carbazole–cyanostilbene-based A–D–A luminophores incorporating ketone-derived acceptors (xanthenone and anthraquinone) that enable precise modulation of excited-state behavior and solid-state emission color. The rigidity and electronic nature of the acceptor units exert a decisive influence on charge-transfer characteristics in solution as well as the solid state. XAN-CZ-CS exhibits emission dominated by a hybridized local and charge-transfer excited state (HLCT) with only limited CT character, whereas the strongly electron-withdrawing and rigid diketone unit in AQ-CZ-CS drives a more pronounced CT state, resulting in stronger solvatochromism and a substantial red shift in THF solution (450 → 635 nm). In the solid state, acceptor-dependent packing and restricted intramolecular motion generate substantial bathochromic shifts, yielding tunable emission from cyan (∼475 nm, ϕ = 10%) to orangish red (∼610 nm, ϕ = 2.7%). Notably, XAN-CZ-CS exhibits fully reversible mechanofluorochromism, while AQ-CZ-CS shows nonreversible MFC behavior. The experimental observations are further supported by DFT, TD-DFT, and NTO analyses, which validate the distinct CT characteristics and the role of acceptor rigidity in directing excited-state processes. Overall, this study highlights acceptor engineering as a powerful strategy for designing multicolor, stimuli-responsive organic luminophores for advanced optoelectronic and security applications.