Thermal Cis-to-Trans Isomerization of Azobenzene-Containing Molecules Enhanced by Gold Nanoparticles: An Experimental and Theoretical Study

Abstract

International audienceWe report on the experimental and theoretical investigation of a considerable increase in the rate for thermal cis -> trans isomerization of azobenzene-containing molecules in the presence of gold nanopartides. Experimentally, by means of UV vis spectroscopy, we studied a series of azobenzene-containing surfactants and 4-nitroazobenzene. We found that in the presence of gold,nanoparticles the thermal lifetime of the cis isomer of the azobenzenecontaining molecules was decreased by up to 3 orders of magnitude in comparison to the lifetime in solution without nanoparticles. The electron transfer between azobenzene-containing molecules and a surface of gold nanopartides is a possible reason to promote the thermal cis trans switching. To investigate the effect of electron attachment to, and withdrawal from, the azobenzene-containing molecules on the isomerization rate, we performed density functional theory calculations of activation energy barriers of the reaction together with Eyring's transition state theory calculations of the rates for azobenzene derivatives with donor and acceptor groups in para position of one of the phenyl rings, as well as for one of the azobenzene-containing surfactants. We found that activation barriers are greatly lowered for azobenzene-containing molecules, both upon electron attachment and withdrawal, which leads, in turn, to a dramatic increase in the thermal isomerization rate

Long‐Distance Rate Acceleration by Bulk Gold

“…It is known that charge transfer can accelerate the cis-trans isomerization rates of azobenzenes.Azobenzenes that are either oxidized to the corresponding radical cations or reduced to the radical anions exhibit very fast thermal isomerization rates. [17] The low cis-trans activation barriers of azobenzenes directly absorbed on gold nanoparticles [18,19] or lying flat on Au-(111) [20] or Bi(111) [21] surfaces have been explained by atransfer of electron density from the azobenzene to the metal. [19] To investigate if such acharge transfer would be operative in our system, we synthesized azobenzene 6,w here an Au + ion is directly connected to the ethinyl group (Scheme S5).…”

“…[17] The low cis-trans activation barriers of azobenzenes directly absorbed on gold nanoparticles [18,19] or lying flat on Au-(111) [20] or Bi(111) [21] surfaces have been explained by atransfer of electron density from the azobenzene to the metal. [19] To investigate if such acharge transfer would be operative in our system, we synthesized azobenzene 6,w here an Au + ion is directly connected to the ethinyl group (Scheme S5). According to the NBO analysis of 6,t he azoethinyl group carries approximately half an elementary charge (À0.508 e).…”

Modulation of Electronic Mobility of a One‐Dimensional Coordination Polymeric Molecular Wire with Light

“…The effect of metal ions on the photoisomerization of azobenzene systems were studied in a Ag I ‐complex with a 24‐membered cyclic azobenzene by Tamaoki (Figure A) where the trans ‐complex was found to be more stable. Scaiano and Santer's groups have reported the enhanced photoswitching rate of acyclic azobenzene systems in presence of AuNPs (Figure B) . These observations prompted us to prepare and explore the properties of a coordination polymer with with the cyclic azobenzene 1 and Ag + ions.…”

“…Scaiano and Santer's groups have reported the enhanced photoswitching rate of acyclica zobenzene systemsi np resence of AuNPs (Figure 1B). [53,54] These observations prompted us to prepare and explore the properties of ac oordination polymer with with the cyclic azobenzene 1 and Ag + ions. The [Ag + -1]C P-2 was prepared by the addition of silver nitrate (AgNO 3 )s alt dissolved in methanolt oas olution of the 1 in acetonitrile, followed by continuous stirring of the mixture at room temperature for 48 hours in dark conditions (Figure 2A).…”

“…The probable reason of this decrease in the activation energy for the thermal cis!trans reversal process can be ascribed to the complextation of the azobenzene ligand with the Ag + ions. [53,54] In the absence of the metal ion, the double bond character of the N=Nd ouble bond restricts the N-N rotation that slows down the thermals witching process. The Ag + ion, upon coordination to 1,i mpartsapartial positive charge to the sulfur atom.…”