Multi-photon patterning of photoactive o-nitrobenzyl ligands bound to gold surfaces

We quantitatively investigate lithographic patterning of a thiol-anchored self-assembled monolayer (SAM) of photocleavable o-nitrobenzyl ligands on gold through a multi-photon absorption process at 1.7 eV (730 nm wavelength). The photocleaving rate increases faster than the square of the incident li...

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Bibliographic Details
Published in:Photochemical & photobiological sciences 2019, Vol.18 (1), p.30-44
Main Authors: Magill, Brenden A., Guo, Xi, Peck, Cheryl L., Reyes, Roberto L., See, Erich M., Santos, Webster L., Robinson, Hans D.
Format: Article
Language:English
Subjects:
Absorption
Biochemistry
Biomaterials
Chemistry
Gold
Incident light
Ligands
Light intensity
Luminous intensity
Photoactivation
Photon absorption
Photons
Physical Chemistry
Plant Sciences
Raman spectroscopy
Self-assembled monolayers
Self-assembly
Surface chemistry
Wavelengths
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Summary:We quantitatively investigate lithographic patterning of a thiol-anchored self-assembled monolayer (SAM) of photocleavable o-nitrobenzyl ligands on gold through a multi-photon absorption process at 1.7 eV (730 nm wavelength). The photocleaving rate increases faster than the square of the incident light intensity, indicating a process more complex than simple two-photon absorption. We tentatively ascribe this observation to two-photon absorption that triggers the formation of a long-lived intermediate aci -nitro species whose decomposition yield is partially determined either by absorption of additional photons or by a local temperature that is elevated by the incident light. At the highest light intensities, thermal processes compete with photoactivation and lead to damage of the SAM. The threshold is high enough that this destructive process can largely be avoided, even while power densities are kept sufficiently large that complete photoactivation takes place on time scales of tens of seconds to a few minutes. This means that this type of ligand can be activated at visible and near infrared wavelengths where plasmonic resonances can easily be engineered in metal nanostructures, even though their single-photon reactivity at these wavelengths is negligible. This will allow selective functionalization of plasmon hotspots, which in addition to high resolution lithographic applications would be of benefit to applications such as Surface Enhanced Raman Spectroscopy and plasmonic photocatalysis as well as directed bottom-up nanoassembly.
ISSN:1474-905X
1474-9092
DOI:10.1039/c8pp00346g