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Enhanced Photochromism of Diarylethene Induced by Excitation of Localized Surface Plasmon Resonance on Regular Arrays of Gold Na

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Enhanced Photochromism of Diarylethene Induced by Excitation of Localized Surface Plasmon Resonance on Regular Arrays of Gold Na Enhanced Photochromism of Diarylethene Induced by Excitation of Localized Surface Plasmon Resonance on Regular Arrays of Gold Nanoparticles Ryohei Yasukuni, Nordin Félidj, Leïla Boubekeur-Lecaque, Stéphanie Lau-truong, Jean Aubard To cite this version: Ryohei Yasukuni, Nordin Félidj, Leïla Boubekeur-Lecaque, Stéphanie Lau-truong, Jean Aubard. En- hanced Photochromism of Diarylethene Induced by Excitation of Localized Surface Plasmon Reso- nance on Regular Arrays of Gold Nanoparticles. ChemPhysChem, Wiley-VCH Verlag, 2020, 21 (22), pp.2614-2619. 10.1002/cphc.202000613. hal-03036870 HAL Id: hal-03036870 https://hal.archives-ouvertes.fr/hal-03036870 Submitted on 9 Dec 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Manuscript Click here to access/download;Manuscript;Chem Phys Chem_final version.docx 1 2 3 Enhanced Photochromism of Diarylethene Induced by Excitation 4 5 of Localized Surface Plasmon Resonance on Regular Arrays of Gold 6 7 8 Nanoparticles 9 10 11 Ryohei Yasukuni,[a,b] Nordin Félidj,*[a] Leïla Boubekeur-Lecaque,[a] Stéphanie Lau- 12 13 [a] [a]** 14 Truong and Jean Aubard 15 16 a Dr. R. Yasukuni 17 18 Present address: Graduate School of Science and Technology, Nara Institute of Science and Technology, 19 20 Ikoma, 8916-5, Japan; 21 22 b Dr. R. Yasukuni, Prof. N. Félidj, Dr. L. Boubekeur-Lecaque, S. Lau-Truong, Prof. J. Aubard 23 24 Université de Paris, ITODYS, CNRS, UMR 7086, 15 rue J-A de Baïf, F-75013 Paris, France 25 26 Corresponding authors: 27 28 * Prof. Nordin.Félidj: [email protected] 29 30 **Jean Aubard: [email protected] 31 32 Abstract 33 34 35 Localized surface plasmon resonance (LSPR) excitation on the photochromic reaction of a diarylethene derivative 36 37 (DE) was studied by surface enhanced Raman scattering (SERS). UV and visible light irradiations transform 38 39 reversibly DE between open-form (OF) and closed-form (CF) isomers, respectively. A mixture of PMMA and DE 40 41 (either OF or CF isomer) was spin-coated onto gold nanorods (GNRs) arrays, designed by electron beam 42 lithography, with two localized surface plasmon resonances (LSPR) at distinct wavelengths, due to their 43 44 anisotropy. The photochromic reaction rates from CF to OF isomers, under LSPR excitation, were monitored 45 46 from SERS spectral changes under different polarizations, on the same GNR substrate to compare the effect of 47 LSPR field strength. It appears that the photoisomerization rate was faster when LSPR was excited with the 48 49 polarization parallel to the GNR long axis. The present results highlight a potential genuine mechanism, from near 50 51 field LSPR excitation, involved in the photochromic enhancement of diarylethene photochromes. 52 53 54 55 56 57 58 59 60 61 62 63 64 65 1 2 Introduction 3 4 Photochromism of organic compounds is defined as a reversible transformation induced by light between two 5 6 [1] 7 isomeric states with different molecular absorption bands. Among various series of organic photochromes, 8 9 diarylethenes (DE) have received much interest during the past 20 years thanks to their interesting photochromic 10 11 properties. These molecules show good efficiency of the photoisomerization process, both in solution and in solid 12 13 states, high fatigue resistance, thermal stability and fast conversion between isomeric states, which makes DE 14 15 [2] 16 promising candidates for optical devices such as single molecular level optical switches and memories. The 17 18 use of DE in practical applications requires however, that more efficient photochromism takes place, at least in 19 20 one direction and this requires an enhancement of the corresponding photo-induced quantum yield. [3] Excitation 21 22 of localized surface plasmon (LSP) resonance of metal nanostructures can be one possibility to induce efficient 23 24 25 photoisomerization. 26 27 The excitation of localized surface plasmon (LSP) resonances, which arise from collective oscillations of free 28 29 electrons at the surface of noble metal nanoparticles (NPs), leads to intense extinction (absorption and scattering) 30 31 bands, mostly in the visible and near –infrared, the spectral position of which depends on the NP size, shape, 32 33 chemical nature and local dielectric environment. In addition, under LSP excitation, the local electromagnetic 34 35 [4] 36 (EM) field is strongly enhanced at the surface of nanostructures. The localized EM field nearby metal 37 38 nanoparticles (NPs), mainly Au and Ag, also leads to giant scattering and emission processes such as Surface 39 40 Enhanced Raman Scattering (SERS) and Surface Enhanced Fluorescence (SEF) which have nowadays various 41 42 applications in the fields of (bio)sensor and chemical analysis.[5] On the other hand, coupling plasmonic 43 44 45 nanoparticles with photochromic molecules could lead, under certain conditions, to an improvement of the 46 47 photoswitching efficiency.[6] The distance between the metallic NPs and the photochromic molecules, and the 48 49 overlap between the LSP resonance and the electronic transition of the photochromic unit have been shown to 50 51 play a major role. Coupling LSPR to molecular resonance induces modifications either on the molecular 52 53 54 properties or on the optical properties of plasmonic nanostructures and these modifications can be detected by 55 56 SERS or by far field extinction spectroscopy. It should be noted that efficient coupling occurs, if and only if an 57 58 optimal distance, molecule/ NPs, is fulfilled and when LSPR and molecular resonances overlap spectrally. Lastly, 59 60 if the molecule is light sensitive, e.g. a photochromic molecule, LSPR excitation could lead to enhanced 61 62 63 64 65 1 2 photochromism. In this latter case, several reports have shown that photoisomerization kinetics were accelerated 3 4 (enhanced) in the presence of gold or silver nanoparticles with respect to the solution photochromism.[7] In these 5 6 7 reports, authors claimed that the photoisomerization rate was increased due to enhanced EM field following LSPR 8 9 excitation. Various effects in the presence of metal (gold and silver) nanoparticles could take place, such as 10 11 nonlinear processes (e.g. two photon process) after light excitation, photo-thermal isomerization due to local 12 13 heating following nonradiative plasmon energy relaxation, charge transfer between molecules and metals, and 14 15 16 they should be taken into account since they could contribute to enhance the isomerization efficiency on the 17 18 plasmonic substrate.[8] In most cases, however, they can hardly be distinguished from the effect of LSPR 19 20 excitation. Moreover, in previous studies, the photoisomerization process was monitored by UV-Visible 21 22 absorption change which is not sensitive enough when analyses at the nanoscale are considered. In addition, such 23 24 25 detection methods could induce some isomerization of the photochromic state under study, which is not relevant 26 27 for an efficient analysis of the genuine mechanism. In an effort to design LSPR based efficient photochromic 28 29 switching systems, the mechanism of photochromic enhancement on metal nanoparticles has to be clarified. 30 31 In this work, the effect of LSPR excitation on the photochromic reaction of a diarylethene derivative (DE) was 32 33 34 studied by surface enhanced Raman scattering (SERS). DE photochromes, either open or closed isomers (resp. 35 36 OF or CF), were deposited by spin coating onto gold nanorods (GNRs) regular arrays. GNRs arrays were 37 38 designed by Electron Beam Lithography (EBL) and display two LSPR modes along the GNR short (S) and long 39 40 (L) axis, respectively. These modes can be selectively excited by switching the excitation light polarization. The 41 42 43 main advantage of using such EBL structures is the possibility to tune in a fine way the LSPR 44 45 wavelengths. Moreover, the EBL fabricated array the metal surface of the NPs is free of any chemical species, 46 47 48 and therefore a chemical reactivity between DE isomers and the metal surface is unlikely, in contrast to 49 50 colloidal NPs. This rule out a contribution by a charge transfer mechanism of the observed enhanced ring - 51 52 opening photochromic reaction. Photoisomerization kinetics from CF to OF isomers was monitored from 53 54 55 SERS intensity changes under the two different polarizations, using 785 nm laser excitation. By this way, it has 56 57 been possible to analyze the contribution of the different processes, arising from near field LSPR excitation, on 58 59 the enhanced photochromism of DE. 60 61 62 Experimental 63 64 65 1 2 Synthesis of 1, 2-bis(5′-ethoxy-2′-(2″-pyridyl)thiazolyl)perfluorocyclopentene (DE) and the characterization of 3 4 its optical properties have already been reported in detail elsewhere.[3] 5 6 7 Plasmonic substrates consisted of gold nanorod arrays were designed by electron beam lithography. In the 8 9 fabrication process, a 100 nm thick layer of poly(methyl methacrylate), PMMA, was spin-casted onto a 10 11 glass/indium tin oxide (ITO, 80 nm thickness) substrate. After chemical development of the exposed areas, 12 13 thermal evaporation of gold and a lift-off procedure followed. The particle height was set at 40 nm. The whole 14 15 2 16 arrays area was fixed to 100 x 100 m . The electron beam lithography has the advantage of the fine control of 17 18 the shape and the spatial arrangement of NPs, allowing the tunability of the LSP resonances which depend on the 19 20 polarization of the incident light.
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