Nitrogen-Doped TiO2 Nanotubes-Catalyzed Synthesis of Small D-pi-A-Type Knoevenagel Adducts and beta-Enaminones

For the first time, interstitial nitrogen-doped TiO2 nanotubes (INDTNTs) have been utilized as heterogeneous green catalysts for the synthesis of D-pi-A-type Knoevenagel adducts (3) and beta-enaminones (6). Notable advantages of the present method include its wide substrate scope, low catalyst loading, avoiding the use of hazardous bases and solvents, products do not require chromatographic purification, high yields, catalyst reusability, etc. The optimized catalyst, INDTNTs-4 has been characterized by XRD, HRTEM, and XPS techniques. The photophysical and electrochemical properties of D-pi-A-type 3 and 6 have been evaluated. The study revealed that the colour tunability (cold white light to orange light) and the HOMO/LUMO levels depend mainly on the presence of various electron donating and withdrawing groups on the aromatic/heteroaromatic rings of 3 and 6. The results indicate that the D-pi-A-type 3 and 6 could be promising materials for the fabrication of optoelectronic devices.