Fig. 5: Density functional theory (DFT) calculations for 1L WSe₂ and nitrophenyl (NPh) oligomers.

The band structure calculations presented here assume a 1% biaxial tensile strain for the 1L WSe₂ substrate. The Fermi energy (E_F) is set to the energy of valence band maximum (VBM). a Pristine, defect-free 1L WSe₂. Here, blue: electronic bands from WSe₂, purple: spin–orbit split bands of WSe₂ that are closest to the VBM and conduction band maximum (CBM) band edges. b 1L WSe₂ with a physisorbed NPh 3-ring oligomer. The real-space distribution of the density of states shows that the valence band maximum retains the WSe₂ character while the lowest energy of the weakly dispersive mid-gap states near the conduction band minimum (CBM) are localized at the NPh oligomer, suggesting the formation of a type-II heterojunction. Although the change in the WSe₂ conduction bands is minimal, there is a finite coupling of the bands to the higher lying NPh orbitals, and thus the conduction bands near CBM are also colored in red. c 1L Wse₂ with a single mono-vacancy of Se, as a prototypical example of defects that can emit light with localized strain. The new mid-gap states near the CBM are localized at the defect site and are colored in green. d, Calculation for the combination of a Se mono-vacancy and NPh 3-ring oligomer. e Illustration of NPh oligomers physisorbed on the surface of 1L WSe₂. In a typical sample, the 4-NBD treatment results in a polydisperse mixture of NPh oligomer species. f Illustration of the quenching mechanism that results in a simplified SPE spectrum following 4-NBD treatment. The represented colors of the band in this illustration follow the color coding used in the calculation in (a–d). Black dashed arrow indicates NPh orbitals and WSe₂ defect states that are in resonance and can effectively quench the emission from these defects. The strain- and defect-trapped exciton thus only recombine radiatively from the available defect states with lower energy that are not quenched by the NPh states (red arrow).