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

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Carbazole-cyanostilbene derivatives are explored for optoelectronic applications.
• Tuning molecular structure influences photophysical properties and solid-state behavior.
• Developing stimuli-responsive and thermally stable luminophores is crucial for advanced applications.

Purpose of the Study:

• To synthesize and characterize carbazole-cyanostilbene luminophores with various diketone acceptors.
• To investigate the effect of acceptor units on emission color, solvatochromism, and aggregation-induced emission (AIE) properties.
• To evaluate the solid-state luminescence, mechanofluorochromism, and thermal stability of the synthesized compounds.

Main Methods:

• Synthesis of carbazole-cyanostilbene derivatives with naphthalimide, anthraquinone, phenanthraquinone, and naphthoquinone acceptors.
• Photophysical characterization including absorption, emission spectra, quantum yields, and solvatochromic studies.
• Aggregation studies, solid-state emission measurements, mechanofluorochromism tests, thermal analysis (TGA), and powder X-ray diffraction (PXRD).
• Computational analysis using Density Functional Theory (DFT) and time-dependent DFT (TD-DFT).

Main Results:

• Naphthalimide (NPCZCS), anthraquinone (AQCZCS), and naphthoquinone (NQCZCS) derivatives showed significant solvatochromic shifts, indicating strong charge-transfer characteristics.
• Phenanthraquinone analogue (PQCZCS) exhibited solvent-independent emission due to a localized excited state.
• NPCZCS and AQCZCS displayed nonclassical AIE behavior, with initial emission enhancement upon aggregation.
• Solid-state studies revealed bright green emission for NPCZCS (522 nm, ϕ = 24%) and orangish red for AQCZCS (610 nm, ϕ = 2.7%).
• Irreversible mechanofluorochromic responses with red shifts were observed for NPCZCS and AQCZCS upon grinding, confirmed by PXRD.
• All derivatives exhibited high thermal stability with decomposition temperatures above 360 °C.
• DFT and TD-DFT calculations supported the experimental photophysical observations.

Conclusions:

• Fine-tuning diketone acceptors in carbazole-cyanostilbene scaffolds allows for precise control over emission color and solid-state properties.
• The developed luminophores demonstrate potential for color-tunable, thermally robust, and stimuli-responsive emissive materials.
• These materials are suitable for next-generation optoelectronic and display applications.