Z-E Isomerization of Azobenzenes Catalyzed by Bare and Core-Shell Gold Nanoparticles

SABRINA SIMONCELLI; PEDRO F. ARAMENDÍA

Maresias-San Pablo

Congreso; XII Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2015

p { margin-bottom: 0.25cm; direction: ltr; color: rgb(0, 0, 0); line-height: 120%; }p.western { font-family: "Liberation Serif","Times New Roman",serif; font-size: 12pt; }p.cjk { font-family: "Droid Sans Fallback"; font-size: 12pt; }p.ctl { font-family: "FreeSans"; font-size: 12pt; }The interaction of metallicnanoparticles (MNPs) with azobenzenes (ABs) has received considerableattention in view of the changes that the photochromic transformationconfers to NP properties and photocontrollable layers on metalsurfaces. MNPs can deactivate the electronic state of organicmolecules placed near their surface, modulating the switchingcapability of the probe. Not so well studied is the isomerizationkinetic rates of azobenzenes placed near MNPs. Scaiano et al. werethe first ones to report the AuNP catalysis of the thermal Z-Eisomerization of unbounded ABs in suspensions of ?pseudo-naked?AuNPs. They reported average rates in AuNP suspension in water. Herewe examine the kinetics of the thermal Z-E isomerization of ABs inAuNPs suspensions to answer the questions: Which is the magnitude ofthe catalytic effect of the AuNPs? Can we obtain the Z-E thermalisomerization rate of azobenzenes over the AuNPs? Which is the roleof the metallic surface? Is it necessary for the photochromiccompound to be in direct contact with the metallic surface or doesthe NP influence on the catalysis extend in volume due to the highpolarizability of the NP plasmonic interaction? We explored thecatalytic effect of 15 nm diameter AuNPs upon the thermal Z-Eisomerization reaction of azobenzene and nine 4 and 4-4' substitutedazobenzenes (ABs). The kinetics follows a first order rate in a rangeof [ABs] = 5 to 50 µM and [AuNPs] = 50 pM to 1 nM. A kineticanalysis of this compartmentalized system renders the thermal Z-Eisomerization rate constant associated to each AuNP, which is 10 to10⁶ fold higher in comparison to the same freeABs in solution. Experiments with selective Au facets coverage, aswell as the kinetics studied in gold-silica core-shell nanoparticles(AuNP@SiO2) of different thickness, demonstrate the surface nature ofthe catalysis and allow to evaluate the diffusion coefficient of ABin the silica layer.