Enhancement of the photochromic switching speed of bithiophene azo dyes

Abstract

A series of heteroaryl substituted bithiophene azo dyes in solution were irradiated with visible light to promote the azo E-Z isomerization and then the kinetics of the thermal Z-E back reaction was studied. The speed of this process is strongly influenced by the nature of the aromatic ring linked to the N=N function. While thiazole bithiophene azo dyes exhibit high switching speeds between the two isomers, but limited interconversion, for benzothiazole and substituted thiadiazole bithiophene azo dyes the switching between the two photoisomers can be performed in 3 seconds with a significant conversion of the trans-isomer to the thermal unstable cis-isomer (19-21%) and therefore a notable variation of the visible spectrum is observed.

A comprehensive spectroscopic, solvatochromic and photochemical analysis of 5-hydroxyquinoline and 8-hydroxyquinoline mono-azo dyes

“…Furthermore, some efficient chromophoric and metallochromic indicators have 8HQ in their structure [34] . The presence of a stable chromophore azo group ( -N = N -) conjugated with an aromatic ring creates a molecule with intense and highly stable color in different solvents throughout the visible region of light [35][36][37][38] . Although numerous papers have described the synthesis and properties of azo-8-hydroxyquinoline [39][40][41][42] , there is no report on the synthesis of similar 5-hydroxyquinoline (5HQ) azo analogous ( Fig.…”

Azobispyrazole Family as Photoswitches Combining (Near-)Quantitative Bidirectional Isomerization and Widely Tunable Thermal Half-Lives from Hours to Years

“…The visible light switch 5-5 showed a t1/2 of 7 h, much higher than that of the other visible light bis-heteroaryl azo switches reported so far. 41,42,[44][45][46][47] In order to understand the thermal Z→E isomerization behavior of azobispyrazole family, we studied their potential energy curves, which indicated that the lowest energy pathway followed inversion mechanism (Figure 5b and Figure S31). Based on the inversion transition states (TSs), their free energy barriers ΔG ‡ (difference in Gibbs free energy between TS and Z-isomer, GTS -GZ) were calculated (Table S17).…”

“…43 By combining electron-rich (thienyl)pyrrole/bithiophene and electron-deficient (benzo)thiazole, a series of push-pull bis-heteroaryl azo switches were constructed, which were responsive to visible light and their Z-isomer t1/2 ranged from milliseconds to seconds. [44][45][46][47] In view of the very limited types of bis-heteroaryl azo switches reported so far and their limitations on bidirectional photoconversion and/or Z-isomer stability, the potential of Het-N=N-Het architecture is far from exploited, calling for the development of new molecular systems.…”

Selectively Biodegradable Polyesters: Nature-Inspired Construction Materials for Future Biomedical Applications

“…The azo group is well known for the photosensitive properties in organic chemistry. The Z -configuration can be easily switched to a more stable E -configuration by specific wavelength irradiation [90]. In the polymer chemistry, the reduction of azo group is taken in advantage and it is widely used for drug delivery systems.…”