The Missing Piece: Concentration Dependence of Donor‐Acceptor Stenhouse Adduct (DASA) Reactivity

Abstract

Donor‐Acceptor Stenhouse Adducts (DASAs) are molecular photoswitches that reversibly isomerize from a linear to a cyclized form upon visible light irradiation. In the cyclized form, these molecules selectively react with a thiol in a thiol‐Michael addition. Driven by the complexity of the switching mechanism and chemical properties of DASAs, the effect of concentration (ranging from 1 to 5 mM DASA) on the thiol‐Michael addition was investigated. We find that the rate limiting step in the reaction is the photochemically induced DASA isomerization, as higher concentrations of thiol do not alter the rate at which the thiol‐Michael adduct (TMA) is formed. Moreover, the kinetics of the product formation were found to be more significantly affected by irradiation at higher concentrations. In two distinct scenarios, where either the concentration or the molar equivalence of the reaction partner was kept constant, the TMA was found to be more efficiently formed under irradiation at higher concentrations. These findings indicate that the DASA reactivity towards thiol‐Michael reactions appear to be equilibrium‐driven at lower concentrations and light‐driven at higher concentrations.

Fatigue of Donor‐Acceptor Stenhouse Adducts in Polymer Matrices and Solution

“…Commercial polymer binders contain various additives such as cross‐linking agents, residual polymerisation initiators, surfactants, and radical scavengers [21] . While additives such as hindered amine light stabilisers (HALS) and UV absorbers are meant to protect the binder from degradation, they have the potential to react with the photochromic dye in both the highly susceptible open and closed DASA structures [6,7] …”

Enhanced Sampling Aided Design of Molecular Photoswitches

“…In particular, the photoswitching mechanism of DASA-based systems starts with an actinic step (E/Z photoisomerization) but is followed by a multitude of competing thermal pathways involving 4p electrocyclization, bond rotation and proton transfer. [23][24][25][26][27][28][29][30][31][32][33][34][35] In our Raucci, U and Sanchez, D. M et al -Enhanced Sampling Aided Design 3 recent work [29][30] we showed for the first time the natural evolution of the nuclear wavepacket relaxing through conical intersections via ab initio nonadiabatic and adiabatic quantum molecular dynamics (Fig. 1).…”

Enhanced Sampling Aided Design of Molecular Photoswitches

“…Unlike previous photoswitches, DASAs can switch from a colored conjugated form to a colorless ring-closed structure via a rather complex multistep mechanism initiated by light with subsequent thermal steps governing the overall switching behavior. In particular, the photoswitching mechanism of DASA-based systems starts with an actinic step ( E / Z photoisomerization) but is followed by a multitude of competing thermal pathways involving 4π-electrocyclization, bond rotation, and proton transfer. − In our recent work, , we showed for the first time the natural evolution of the nuclear wavepacket relaxing through conical intersections via ab initio nonadiabatic and adiabatic quantum molecular dynamics (Figure ). Our dynamics suggested that several pathways are accessible on the electronic ground state beyond the main photoswitching mechanism.…”

“…Unlike previous photoswitches, DASAs are capable of switching from a colored conjugated form to a colorless ring-closed structure via a rather complex multistep switching mechanism involving an actinic step coupled to a multitude of competing thermal pathways. [18][19][20][21][22][23][24][25][26][27][28][29][30] Recently, we showed for the first time the natural evolution of this entire photochemical process using ab initio nonadiabatic and adiabatic quantum molecular dynamics, revealing several competing pathways involving E/Z photoisomerization, Raucci, U and Sanchez, D. M et al -Enhanced Sampling Aided Design 3 4p-electrocyclization, bond rotation, and proton transfer (Fig. 1).…”