Defect-Based Modulation of Optoelectronic Properties for Biofunctionalized Hexagonal Boron Nitride Nanosheets.

Defect engineering potentially allows for dramatic tuning of the optoelectronic properties of two-dimensional materials. With the help of DFT calculations, a systematic study of DNA nucleobases adsorbed on hexagonal boron-nitride nanoflakes (h-BNNFs) with boron (VB ) and nitrogen (VN ) monovacancies is presented. The presence of VN and VB defects increases the binding strength of nucleobases by 9 and 34 kcal mol-1 , respectively (h-BNNF-VB >h-BNNF-VN >h-BNNF). A more negative electrostatic potential at the VB site makes the h-BNNF-VB surface more reactive than that of h-BNNF-VN , enabling H-bonding interactions with nucleobases. This binding energy difference affects the recovery time-a significant factor for developing DNA biosensors-of the surfaces in the order h-BNNF-VB >h-BNNF-VN >h-BNNF. The presence of VB and VN defect sites increases the electrical conductivity of the h-BNNF surface, VN defects being more favorable than VB sites. The blueshift of absorption peaks of the h-BNNF-VB -nucleobase complexes, in contrast to the redshift observed for h-BNNF-VN -nucleobase complexes, is attributed to their observed differences in binding energies, the HOMO-LUMO energy gap and other optoelectronic properties. Time-dependent DFT calculations reveal that the monovacant boron-nitride-sheet-nucleobase composites absorb visible light in the range 300-800 nm, thus making them suitable for light-emitting devices and sensing nucleobases in the visible region.