Highly Luminescent TCNQ in Melamine

Area of Science:

• Materials Science
• Photochemistry
• Crystallography

Background:

• Molecular optical properties are highly sensitive to environmental interactions.
• 7,7,8,8-tetracyanoquinodimethane (TCNQ) typically exhibits limited luminescence in solution.

Purpose of the Study:

• To enhance the luminescence of TCNQ by encapsulating it within a crystalline matrix.
• To investigate the mechanism of luminescence enhancement and the role of impurities.

Main Methods:

• Single-crystal X-ray diffraction for structural analysis.
• Mass spectrometry and UV-Vis spectroscopy for impurity identification.
• Density-functional theory (DFT) calculations for theoretical elucidation.
• Fluorescence spectroscopy for optical property characterization.

Main Results:

• Colored single crystals of melamine doped with TCNQ were successfully synthesized.
• Impurities identified as neutral TCNQ and its oxidation product, dicyano-p-toluoyl cyanide anion (DCTC-).
• Encapsulated TCNQ exhibits bright fluorescence centered at 450 nm with 19% quantum yield and 2 ns lifetime.

Conclusions:

• Crystalline melamine acts as a host matrix that significantly enhances TCNQ luminescence.
• The concentration of TCNQ and DCTC- impurities can be controlled by precursor molar ratios.
• This encapsulation strategy offers a promising route to induce fluorescence in other non-luminescent molecules.