Abstract
Azoheteroarene photoswitches have attracted attention due to their unique properties. We present the stationary photochromism and ultrafast photoisomerization mechanism of thiophenylazobenzene (TphAB). It demonstrates impressive fatigue resistance and photoisomerization efficiency, and shows favorably separated (E)‐ and (Z)‐isomer absorption bands, allowing for highly selective photoconversion. The (Z)‐isomer of TphAB adopts an unusual orthogonal geometry where the thiophenyl group is perfectly perpendicular to the phenyl group. This geometry is stabilized by a rare lone‐pair⋅⋅⋅π interaction between the S atom and the phenyl group. The photoisomerization of TphAB occurs on the sub‐ps to ps timescale and is governed by this interaction. Therefore, the adoption and disruption of the orthogonal geometry requires significant movement along the inversion reaction coordinates (CNN and NNC angles). Our results establish TphAB as an excellent photoswitch with versatile properties that expand the application possibilities of AB derivatives.
Highlights
The operation of molecular photoswitches is based on the reversible transformation of the switching molecule between states of different physicochemical properties.[1]
We present the stationary photochromism and ultrafast photoisomerization mechanism of thiophenylazobenzene (TphAB)
Our theoretical calculations demonstrate that the (Z)-isomer of TphAB adopts a geometry where the thiophene ring is perfectly orthogonal to the phenyl ring, with the S-atom facing the phenyl ring
Summary
Azobenzenes (AB) are a prominent group of widely utilized photoswitches They are highly fatigue-resistant and relatively easy to synthesize.[3] The photochromism of ABs is based on the EQZ photoisomerization of the central N=N bond, which results in substantial geometric and spectral changes.[4] Spectrally, ABs are characterized by a strong p!p* transition band (S2), typically located in the 300– 350 nm range for the (E)-isomer and the 250–290 nm range for the (Z)-isomer. Due to distortions because of steric effects, the spectral properties of azoheteroarenes are altered This often results in a favorable separation of the (E)- and the (Z)-isomer bands that permits > 98 % conversion in each direction.[12a,b,d] choice, position, and orientation of the heteroaryl and its substituents represent a new tuning dimension for ABs. the presence of heteroatoms permits new functional designs previously unavailable in conventional ABs. azoheteroarenes offer an untapped potential for further optimization and expansion of the capabilities of AB photoswitches. We present its synthesis along with the theoretical and experimental investigation of the photoisomerization of this thiophenylazobenzene (TphAB) photoswitch
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