Synthesis and energy band characterization of hybrid molecular materials based on organic–polyoxometalate charge-transfer salts

• Charge-transfer salts are obtained by self-assembling POMs with an anthracene cation.
• Their energy parameters are comparable to those of optoelectronic materials in OLEDs.
• These POM-based hybrids could be applied in the area of optoelectronic devices.

A cationic amphiphilic molecule was synthesized and employed to encapsulate Lindqvist ([M6O19]2−) and Keggin polyoxometalates ([SiM12O40]4−, M=Mo, W) to form hybrid molecules through electrostatic interaction. The X-ray diffraction results illustrate that the former hybrids possess lamellar nanostructures in their solid states, while the latter hybrids show a cubic Im3m packing model with low intensities and poor long-range order. These hybrids have clear charge-transfer characters as shown in their deeper colors and UV–vis diffuse reflectance spectra. According to the reported reduction potentials of the POM acceptors and the band gaps deduced from their diffuse reflectance spectra, we have calculated the theoretical values of the lowest unoccupied molecular orbital (LUMO) position similar to the electron affinity (EA) of solid materials. Such energy level parameters are comparable to those of electroluminescence and electron-transport materials commonly used in organic electroluminescence devices. These organic–polyoxometalate charge-transfer salts have more advantages, such as higher decomposition temperatures, easier film fabrication and better electron affinities, which presumably would be used for electron-transport materials in the area of the electroluminescence.

Hybrid molecular materials with charge-transfer characters formed by a positively charged donor L and acceptors of the Lindqvist-type and Keggin-type POMs have lamellar and cubic structures in their solid state.Figure optionsDownload as PowerPoint slide