Abstract
AbstractPlasmonic enhancement of absorption in charge‐transfer (CT) complexes formed under NO2 gas adsorption onto 2D hybrid structure, based on the metal–organic monolayer and gold nanoparticles (AuNPs), is demonstrated. By using Langmuir–Blodgett deposition of low‐symmetry zinc phthalocyanine (ZnPc) molecules, the metal–organic monolayer is fabricated with greatly suppressed intermolecular aggregation. Oxidation of the monolayer through coordination of NO2 molecules with axial zinc ions of ZnPc molecules gives rise to the specific absorption band inherited to cation radical ZnPc+. The hybrid AuNPs–ZnPc structure is engineered to maximize exciton–plasmon interaction of CT complexes at the radical form of the metal–organic monolayer. Excellent spectral and spatial overlaps with plasmon resonance boost absorption of CT internal optical transition, so‐called “fingerprint” band, by a factor of six from 0.45% to 2.8% in total. The approach paves the way for efficient plasmonic control over photochemical reactions promoted by charge‐transfer complexes in metal–organic films. In particular, the plasmonic effect is harnessed to improve NO2 gas sensing properties; the experimental study shows a 15‐fold increase of the detection efficiency in the specific band of CT complexes under the gas exposure.
Highlights
Results and DiscussionTo form the densely packed monolayer of gold nanoparticles, we implement in situ control of both: its surface pressure and absorption spectra
Under NO2 gas adsorption onto 2D hybrid structure, based on the metal– organic monolayer and gold nanoparticles (AuNPs), is demonstrated
We identify the collapse point from absorption spectra of the Langmuir AuNPs monolayer measured in situ at different subphase area and pressure as shown in Figure 1b The absorption band centered at ≈530 nm corresponds to localized surface plasmon (LSP) resonance in gold nanoparticles
Summary
To form the densely packed monolayer of gold nanoparticles, we implement in situ control of both: its surface pressure and absorption spectra. Within the picture of weak excitonplasmon interaction, there are two primary effects behind the increase of optical density: plasmonic enhancement of absorption in ZnPc molecules nearby gold nanoparticles[24] and LSP resonance amplification due to the high refractive index of surrounding ZnPc monolayer To discriminate between these contributions and extract pure enhancement factor of ZnPc absorption in the hybrid structure, we calculate E-field distribution acting on the molecules and integrate over the whole ZnPc layer. To gain more insight into origins of the large enhancement at this specific band, we have simulated the spectra using modified complex permittivity of ZnPc+-NO2− layer which we derived from experimental data by means of Kramers–Kronig analysis using absorption spectrum of the bare ZnPc monolayer under NO2 exposure Plasmon enhanced absorption of CT complexes is the main contribution to the “fingerprint”LSP band and underlying mechanisms for the improved NO2 gas sensing properties
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call