The Role of Structural Flexibility in Plasmon‐Driven Coupling Reactions: Kinetic Limitations in the Dimerization of Nitro‐Benzenes

Abstract

molecules simultaneously, which facilitates coupling reactions of two or more molecules. [7][8][9] On the other hand, nanoscale heating can increase the speed of molecular reorganization and surface diffusion, thereby increasing the rate of favorable reactive encounters. Several important examples of plasmon-driven bond formation were demonstrated in recent years, [10,11] including CC bond formation in hydrocarbons, [7,12] Suzuki-Miyaura type reactions, [13] and molecular dimerization reactions by NN bond formation. [7,14,15] Until recently, the question if the dominating effect of plasmonic nanoparticles is to act as charge donors [16,17] or heat sources [14,18] has been heavily debated. Nowadays, most authors agree that depending on the reaction, one or the other effect can dominate. [19] For example, the dissociation of diatomic compounds on gold-particles, in particular of H 2 [1,20] and O 2 , [21,22] is likely determined by the transfer of energetic electrons, while the fragmentation of organic molecules, such as the decomposition of dicumyl-peroxide, [18] is rather dominated by the plasmon-mediated photo-heating. Although much progress has been made in understanding such dissociation reactions, our understanding of plasmon-driven multistep bond-formation processes is still in its infancy. In these reactions, different reaction steps might profit from the presence of plasmonic excitations. As a prominent example, the dimerization reaction of 4-nitrothiophenol (4NTP) to 4-4′-dimercaptoazobenzene (DMAB) was confirmed by many

The electronic structure of the metal–organic interface of isolated ligand coated gold nanoparticles

“…(iii) In addition, also an electron transfer from the metal to the molecule affects the work function, which has been described elsewhere in more detail for the present system. 37 …”

“…(iii) In addition, also an electron transfer from the metal to the molecule affects the work function, which has been described elsewhere in more detail for the present system. 37 (iv) A fourth effect is a possible shi of the Au 4f signals due to the different chemical environment of the gold sulfur bond. The shi for NTP coupled to a single Au atom compared to pure Au has been calculated by DFT to be 1.3 eV to higher BE, which is in good agreement with previously reported values for Au-S 65 and other hybridized Au species.…”

“… 34 Recently, it has been demonstrated by comparing the plasmon mediated formation of diazo bonds from NTP and 4-nitrobenzylmercaptan (NBM) that the reaction kinetics are significantly influenced by the molecular geometry. 37 The in-depth knowledge of the electronic properties at the molecule–NP interface allows efficient tuning of the kinetics of plasmon mediated electron transfer reactions. 38 Therefore, the following needs to be understood:…”

Colloidal black gold with broadband absorption for photothermal conversion and plasmon-assisted crosslinking of thiolated diazonium compound

“…1440 cm -1 are not related to the original MBD molecules but rather to an azobenzene derivative (Figure 5a), similar to the very common dimercaptoazobenzene (DMAB). 11,26 Also, the peak for the N2 + stretching around 2200 cm -1 is not observed. Since the diazonium moiety is very reactive, it is possible that the self-assembled MBD molecules are sufficiently close to each other on the gold surface to react with each other and dimerize.…”

“…First, the Raman spectra showed that the diazonium molecules are selfassembled in a dimer form, resembling the typical DMAB structures. 26 Second, upon continuous excitation of the surface plasmon, the Raman peak assigned to the N=N vibrational modes decreases in intensity, while the C=C peak is broadened with time, suggesting the crosslinking of the adsorbed molecules accompanied by removal of the nitrogen.…”