In\nSitu Photoreversible\nTuning of Chemical Interface\nDamping in Single Gold Nanorods Through Cucurbit[8]uril-Based Host–Guest\nInteractions

Chemical interface damping (CID)\nis a recently proposed\nplasmon-damping\npathway based on the interfacial hot-electron transfer from metal\nto adsorbate molecules. However, the in situ reversible tuning of\nCID in single gold nanorods (AuNRs) has remained a considerable challenge.\nIn this study, we used total internal reflection scattering microscopy\nand spectroscopy to investigate the CID induced by <i>p</i>-aminoazobenzene (<i>p</i>-AAB), which has fast photoisomerization\ncharacteristics, attached to single AuNRs. We demonstrated the in\nsitu reversible tuning of CID in single AuNRs by switching between\nultraviolet (UV, 365 nm) and visible (vis, 465 nm) irradiation to\ninduce photoresponsive structural conversions between the cis and\ntrans forms of <i>p</i>-AAB in ethanol, leading to different\nlowest unoccupied molecular orbital (LUMO) energies for both forms.\nThe localized surface plasmon resonance (LSPR) line width was wide\nunder vis irradiation but narrow under UV irradiation, indicating\nthat hot electrons are more efficiently transferred to <i>trans</i>-<i>p</i>-AAB with a low LUMO energy level. We further\ninvestigated the in situ photoreversible tuning of CID by manipulating\nsupramolecular host–guest interactions between cucurbit[8]uril\n(CB[8]) and <i>p</i>-AAB in the single AuNRs. Additionally,\nreal-time in situ reversible tuning of CID in single AuNRs was achieved\nthrough photonic switching of the cis–trans forms of <i>p</i>-AAB inside CB[8]. The LSPR line width was narrow under\nvis irradiation but gradually widened under UV irradiation before\nnarrowing again upon returning to vis irradiation, unlike the case\nwith <i>p</i>-AAB only. These results can be ascribed to\nthe fact that <i>cis</i>-<i>p</i>-AAB completely\nencapsulated within CB[8] in water is thermodynamically more favorable\nthan <i>trans</i>-<i>p</i>-AAB. Therefore, we\nhave discovered a new strategy for tuning the CID by performing <i>p</i>-AAB photoisomerization and adjusting the wavelength of\nincident light in single AuNRs. In addition, this study demonstrates\nthat CID can be effectively applied to the development of biosensors\nto detect guest molecules and their structural changes inside the\ncavity of CB[8] in single AuNRs.