4 research outputs found
Mechanism of plasmon-induced catalysis of thiols and the impact of reaction conditions
Plasmon-induced catalysis of the thiols 4-aminothiophenol (ATP) and 4-nitrothiophenol (NTP) has been investigated in numerous studies. Currently, two reaction pathways are discussed in the literature, one leading to dimerization to 4,4’-dimercaptoazobenzene (DMAB), and the other, depending on experimental conditions, resulting in a monomer commonly assigned to ATP. In this joint experimental-theoretical study, we disentangle the involved photo-/plasmon-mediated reaction mechanisms by thorough control of the reaction conditions, particularly the involved surface-enhanced Raman scattering (SERS) substrates. The Raman spectra experimentally and strongly suggest that the formation of a new stable intermediate plays a crucial role. Tracking the reaction with time-dependent SERS experiments allows us to build the connection between the dimer (DMAB) and monomer pathways and to propose potential reaction pathways for different environmental conditions. Furthermore, theoretical modelling addressing the excited-states properties of key intermediates involved in both reaction pathways and the respective thermodynamics allows to investigate the underlying reaction mechanism in more detail – complementing the spectroscopic results
Mechanism of Plasmon-Induced Catalysis of Thiolates and the Impact of Reaction Conditions
The conversion of the thiols 4-aminothiophenol (ATP)
and 4-nitrothiophenol
(NTP) can be considered as one of the standard reactions of plasmon-induced
catalysis and thus has already been the subject of numerous studies.
Currently, two reaction pathways are discussed: one describes a dimerization
of the starting material yielding 4,4′-dimercaptoazobenzene
(DMAB), while in the second pathway, it is proposed that NTP is reduced
to ATP in HCl solution. In this combined experimental and theoretical
study, we disentangled the involved plasmon-mediated reaction mechanisms
by carefully controlling the reaction conditions in acidic solutions
and vapor. Motivated by the different surface-enhanced Raman scattering
(SERS) spectra of NTP/ATP samples and band shifts in acidic solution,
which are generally attributed to water, additional experiments under
pure gaseous conditions were performed. Under such acidic vapor conditions,
the Raman data strongly suggest the formation of a hitherto not experimentally
identified stable compound. Computational modeling of the plasmonic
hybrid systems, i.e., regarding the wavelength-dependent character
of the involved electronic transitions of the detected key intermediates
in both reaction pathways, confirmed the experimental finding of the
new compound, namely, 4-nitrosothiophenol (TP*). Tracking the reaction
dynamics via time-dependent SERS measurements allowed us to establish
the link between the dimer- and monomer-based pathways and to suggest
possible reaction routes under different environmental conditions.
Thereby, insight at the molecular level was provided with respect
to the thermodynamics of the underlying reaction mechanism, complementing
the spectroscopic results
Mechanism of Plasmon-Induced Catalysis of Thiolates and the Impact of Reaction Conditions
The conversion of the thiols 4-aminothiophenol (ATP)
and 4-nitrothiophenol
(NTP) can be considered as one of the standard reactions of plasmon-induced
catalysis and thus has already been the subject of numerous studies.
Currently, two reaction pathways are discussed: one describes a dimerization
of the starting material yielding 4,4′-dimercaptoazobenzene
(DMAB), while in the second pathway, it is proposed that NTP is reduced
to ATP in HCl solution. In this combined experimental and theoretical
study, we disentangled the involved plasmon-mediated reaction mechanisms
by carefully controlling the reaction conditions in acidic solutions
and vapor. Motivated by the different surface-enhanced Raman scattering
(SERS) spectra of NTP/ATP samples and band shifts in acidic solution,
which are generally attributed to water, additional experiments under
pure gaseous conditions were performed. Under such acidic vapor conditions,
the Raman data strongly suggest the formation of a hitherto not experimentally
identified stable compound. Computational modeling of the plasmonic
hybrid systems, i.e., regarding the wavelength-dependent character
of the involved electronic transitions of the detected key intermediates
in both reaction pathways, confirmed the experimental finding of the
new compound, namely, 4-nitrosothiophenol (TP*). Tracking the reaction
dynamics via time-dependent SERS measurements allowed us to establish
the link between the dimer- and monomer-based pathways and to suggest
possible reaction routes under different environmental conditions.
Thereby, insight at the molecular level was provided with respect
to the thermodynamics of the underlying reaction mechanism, complementing
the spectroscopic results