Mechanistic Insights into the Triplet Sensitized Photochromism of Diarylethenes

Abstract

Operating photoswitchable molecules repetitively and reliably is crucial for most of their applications, in particular in (opto)electronic devices, and related to reversibility and fatigue resistance, which both critically depend on the photoisomerization mechanism defined by the substitution pattern. Two diarylethene photoswitches bearing biacetyl triplet sensitizers either at the periphery or at the core were investigated using both stationary as well as transient UV/Vis absorption spectroscopy ranging from the femtosecond to the microsecond time scale. The diarylethene with two biacetyl moieties at the periphery is switching predominantly from the triplet excited state, giving rise to an enhanced fatigue resistance. In contrast, the diarylethene bearing one diketone at the photoreactive inner carbon atom cyclizes from the singlet excited state and shows significantly higher quantum yields for both cyclization and cycloreversion.

Molecular photoswitches in aqueous environments

“…350 The properties of DTEs, such as QYs, 351,353,354 PSDs, 353 and wavelength of irradiation for O-C photo-interconversion 355,356 were subject of extensive study and optimization. The characteristics and the efficiency of the O-C interconversion strongly depends on structural properties, such as the type of bridging moiety, 333,335,338,357 the nature of the (hetero)aromatic ring or the substituents of the aryl rings 358,359 or at the reactive carbon, 354,360 and the influence of the used solvent. 357 While the QY of the closing reaction F O-C is between 0.21 and 0.59 for differently substituted perfluoro cyclopentene bridged derivatives in n-hexane, 331 and QYs up to 1.0 were measured for Fig.…”

“…23B). 356,360 DAEs with (perfluorinated) cyclopentadiene bridges can be switched reversibly over several cycles in the solid state 331,361 and in a wide range of solvents, including water, 358 aqueous buffer, and 349,370 in living cells. 371 However, by changing the bridging moiety to electron-acceptor moieties such as maleimide, 333 maleic anhydride, 357 or benzoquinone, 338 the O -C reaction is suppressed in polar solvents and hence, cannot proceed in water and water/co-solvent mixtures (Fig.…”

Expanding excitation wavelengths for azobenzene photoswitching into the near-infrared range via endothermic triplet energy transfer

“…Triplet-sensitized Z -to- E isomerization of azobenzenes is an especially viable approach for indirect excitation due to its reversibility, non-destructivity and near-unity conversion efficiency. 26,29,31 Triplet sensitization has also been utilized to isomerize other types of photoswitches, such as overcrowded alkenes, 32 diarylethenes, 33 stilbenes 34 and indigos. 35 However, in previous reports triplet sensitizers have been excited in the UV-to-yellow (<580 nm) range, while the capabilities of potent red and NIR-absorbing triplet sensitizers, such as porphyrins, have not been utilized in azobenzene photoswitching.…”

Future‐Oriented Advanced Diarylethene Photoswitches: From Molecular Design to Spontaneous Assembly Systems

“…Thus, the influence of π‐conjugation (formed by biacetyl moieties and the DAE core) as a triplet sensitizer changed significantly as different sites were modified. [ 31a ]…”

“…[29] In recent years, many strategies have been developed to avoid the direct excitation of DAE by UV light, [30] including making changes to the structural design of the DAE molecule itself, such as by using an extended π-conjugated system. [29] In addition, the interaction between the triplet sensitizer unit and the DAE core, [31] an upconversion strategy using rare earth metal nanoparticles, [32] and a multiphoton absorption process [19d,33] are all promising methods. In the practical application of a new generation of DAE molecules, the assembly strategy for DAE and other molecular components plays a key role.…”