Isatin N²-diphenylhydrazones: new easily synthesized Vis-Vis molecular photoswitches

Abstract

The photochromic properties of isatin N 2 -diphenylhydrazones as a new type of molecular switches were investigated. Interestingly, dimerization stabilizes the formation of only E-isomers in synthesis, even without Z-isomer presence in the mother liquor. The irradiation of E-isomers in solution at their absorption maxima leads to the formation of the corresponding Z-isomers. Although the shift in absorption maximum is not large and photochemical quantum yields are lower compared than in commonly used photoswitches, the absorbance changes are sufficient for potential practical use of these compounds as On-Off switches when the readout wavelength is optimally selected. The process is reversible and switching cycles can be repeated many times in both directions. Determined thermodynamic parameters and calculated geometry of the transition state clearly indicate the inverse mechanism of thermally initiated slow back Z-E isomerization. Due to the Vis-Vis character of molecular photoswitching and significant geometric changes during the switching process, isatin N 2 -diphenylhydrazones are eminently suitable for molecular switching in biological/biotechnological applications. Moreover, the interaction of isatin N 2 -diphenylhydrazones with strongly basic anions increases their functionality and creates a four-state On-Off switch in one molecule. This four-state switch includes the unique E-Z isomerization induced photochemical switching between two stable tautomeric forms of organic amide anion. Simple synthesis of these derivatives and their sufficiently sensitive response to external stimuli promote isatin N 2 -diphenylhydrazones as suitable candidates for both discussed photochemistry areas (molecular switching and actinometry).

Isatin-1,8-Naphthalimide Hydrazones: A Study of Their Sensor and ON/OFF Functionality

“…It also appeared in the ultraviolet-visible (UV-Vis) spectra (Table 1). Compared to the isatin N 2 -diaryl hydrazones or arylhydrazones these compounds have a long absorbent band, which is batochromically shifted at least about 30 nm [1,2]. The maximum band position is at 460 nm and depends a little on solvent polarity.…”

“…The photochromic molecules ability “to function” as molecular switches and to communicate with other chromophores create conditions for on Boolean’s logic working photonic gates formation. In our previous works the isatin N 2 -diarylhydrazone [1] or arylhydrazones [2,3] and their deprotonated forms were examined with the aim to use them as organic material for electronics or anion sensors. The UV-Vis spectra of these compounds are similar.…”

Detailed solvent, structural, quantum chemical study and antimicrobial activity of isatin Schiff base

“…Investigated isatin derivatives showed chemical shift of the azomethine carbon in the range of 150.43-156.72 for E isomer, and 150.90-155. 16 for Z isomer listed in Table S6.…”

“…Also, the mechanism of photochemically and thermally initiated E-and Z-isomer transformations in solvents of different polarity, was investigated on two isatin N-phenylsemicarbazone colorimetric sensors [15]. In other studies, the photochemical (irradiation) and thermal treatment of the E-isomers of isatin N 2 -diphenylhydrazones leads to the transformation to Z-isomers in a reversible process [16].…”

Structural and Spectroscopic Properties of Benzoylpyridine‐Based Hydrazones

“…Photoswitches with short half‐life of the back thermal reaction of thermodynamically less stable form are T‐type photoswitches, whereas those with long half‐life are classified as P‐type photoswitches. Among new photochromic compounds, hydrazone photoswitches represent a really important family of (particularly) the P‐type photoswitches, mainly due to their extraordinarily high thermal stability (half‐lives up to 5,300 years), straightforward synthesis, easy skeleton modularity, high photostability (fatigue resistance) and even bistable fluorescence On‐Off response [4–19] . Interestingly, the Aprahamian research group recently introduced light‐induced regulation of transparency of nematic liquid crystals containing a chiral dopant attached to two hydrazone‐based photoswitches, [20] or, for example, reported fluorescent bistable amphiphilic copolymers containing hydrazone photoswitches whose Z to E photoisomerization leads to an expansion of the copolymer nanoparticle and thus to the regulation of drug release (cytotoxicity) monitored by quenching of hydrazone fluorescence [21] …”