Fluorescence and physical properties of the organic salt 2-chloro-4-nitrobenzoate–3-ammonium-phenol

• Organic salt of 2-chloro-4-nitrobenzoate–3-ammonium-phenol (CNBA− · AP+) was grown by solution growth technique.
• Single crystal X-ray diffraction demonstrate that two molecules were linked via N+–H⋯O− interactions.
• The narrow spatial overlap between HOMO and LUMO leads to low ΔEST = 73 meV.
• The fluorescence emission was observed at ≈338 nm with Stokes shift of 53 nm.
• The melting point of CNBA− · AP+ is 187 °C which is higher than the individual components.

Organic salt 2-chloro-4-nitrobenzoate (CNBA−) 3-ammonium-phenol (AP+) exhibits fluorescence at 338 nm in solution and frontier molecular orbitals generated from TDDFT calculations indicate that the ground state and the excited state are physically separated on AP+ and CNBA−. The crystal structure and physical–chemical properties of the CNBA− · AP+ were investigated using X-ray single crystal and powder diffraction, SEM, FTIR, UV–Vis–NIR, and fluorescence spectrometry. X-ray diffraction demonstrates that the two molecules are linked via N+–H⋯O− ammonium–carboxylate interactions, as expected considering their interaction propensities. Proton transfer has been confirmed by FTIR analysis. The melting point of CNBA− · AP+ was observed at 186 °C, which is higher than pure CNBA (140 °C) or AP (120 °C). The observation of a spatially separated HOMO and LUMO possessing a narrow ΔEST = 73.3 meV and an emission in the blue region is promising as an alternative method for the production of OLED materials.

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