Covalent Functionalization of Two-Dimensional Black Phosphorus Nanosheets with Porphyrins and Its Photophysical Characterizations

Black phosphorus nanosheets (BPNSs) are a rising star among 2D materials and hold applications in a wide range of research areas. However, the poor stability of BPNSs due to chemical degradation in the presence of air and water limits their practical applications. Chemical functionalization is a promising strategy to improve the stability and impart new properties to BPNSs. Herein, functional porphyrin units are attached onto BPNSs through a direct phosphorus–carbon linkage using diazonium chemistry. The porphyrin functionalized BPNSs are characterized using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR) and transmission electron microscopy (TEM) analyses. The formation of a P–C bond between BPNSs and porphyrin units is confirmed by the appearance of a new peak at 131.16 eV in the high resolution P 2p XPS spectrum. A control experiment under similar conditions with diazonium free porphyrins further supports the covalent attachment by precluding noncovalent interactions between porphyrins and BPNSs in the hybrid. Furthermore, the photophysical properties of the BPNS–TPP hybrid were investigated in detail using steady state and time-resolved spectroscopic techniques. Importantly, the porphyrin functionalized BPNSs exhibit an improved ambient stability compared to pristine BPNSs, confirmed by UV-Vis absorption and XPS measurements. This study proposes a potential useful route to obtain stable functional BPNSs, holding promising applications in optoelectronic devices such as nonlinear optics and solar energy harvesting devices