The light induced behaviour of siloxane substituted azobenzene compounds in the presence of alkylene spacers is reported for the first time. Firstly, these photosensitive compounds were synthesized and elucidated the molecular structure by spectral analysis such as NMR, FTIR, and UV/Vis. Photoisomerization effect was evaluated in solution and also in nematic phase. The photosaturation occurred exactly at 29 seconds, whereas thermal back relaxation was observed ranging from 19.8 to 23.8 hours. Long duration of the thermal back relaxation is due to the presence of sterically hindered siloxane group substituted to the azobenzene molecules. Decrease in the duration of
The data can be optically stored by a device with the influence of suitable light. The phenomenon is called optical storage and the gadget is known as optical storage device [
Generally, light induced properties of azobenzene differ with varieties of structure, spacers, and functional group associated with it. Mainly, optical activity depends on the number of alkylene spacers present in the molecular structure [
Organosilicons are the derivatives of silane (SiH4). Generally, silane is spontaneously flammable and hydrolyses rapidly with atmospheric moisture [
The azobenzene derivatives are sterically hindered by bulky siloxane group [
The materials include ethyl-4-aminobenzoate (Fluka), sodium nitrite (Aldrich), hydrochloric acid (Fluka), sodium hydroxide (Fluka), methanol (Fluka), phenol (Aldrich), 4-bromo-1-butene (Fluka), 5-bromo-1-pentene (Fluka), 6-bromo-1-hexene (Fluka), potassium carbonate (Aldrich), potassium iodide (Aldrich), acetone (Fluka), potassium hydroxide (Aldrich), toluene (Fluka), Karstedt’s catalyst (Aldrich), and 1,1,1,3,5,5,5-heptamethyltrisiloxane (Aldrich). Acetone was dried over phosphorus pentoxide (Fluka) and dichloromethane was dried over calcium hydride (Fluka) and distilled out before the use. Other solvents and chemicals were used as such.
Instrumental details are as follows. IR spectra were recorded using a Perkin Elmer (670) FTIR spectrometer. 1H NMR (500 MHz) and 13C NMR (125 MHz) were recorded in Bruker. The photoswitching study was performed using UV-visible spectrophotometer from Ocean Optics (HR2000+). For photoswitching studies in solutions, the compounds were dissolved in chloroform at fixed concentration of
The siloxane substituted azobenzene derivatives (
Synthetic scheme for halogen substituted azo dyes.
The solution of 4-ethyl amino benzoate (7.59 g, 46.00 mmol) was prepared by methanol (40 mL) and cooled to 0–2°C. 25% HCl was added dropwise to the solution at 2°C. The solution of sodium nitrite (3.03 g, 44.6 mmol) was prepared in water and added to the reaction mixture dropwise at 2°C for 15 minutes. Then, phenol (4.19 g, 44.6 mmol) was dissolved in methanol and slowly added to the reaction mixture at 2°C. Next, 1 N NaOH solution was added to the reaction mixture to increase the pH (around 8.5–9.0) and reaction mixture was stirred for 4 hours. Finally, the reaction mixture was poured into the beaker containing crushed ice with methanol (250 mL). The solution was filtered to collect the reddish brown precipitate and it was dried and recrystallized with methanol. A red coloured solid; yield: 82%; melting point: 160.2–160.5°C; IR (KBr Pellet)
The solution of
Dried precipitate (
These azo bridged compounds consist of siloxane substitution at one side and carboxylic acid substitution at another side. Tacitly, these compounds were characterized using UV-Vis light to evaluate the photoswitching properties. The compounds
In photoisomerization of
The absorption of the solutions of
Spectroscopic studies showed that thermal back relaxation of the compounds
Thermal back relaxation of the compounds
Usually, the back relaxation decreases when the spacer length increases [
Comparison of thermal back relaxation with spacers.
Exactly 5% of
Fabricated optical storage device by using the compound
Photoisomerization of
In Figure
The prototype of liquid crystal cell was prepared to prove the ability of the siloxane substituted azobenzene compound
Figure
The determination of photostability of
Siloxane substituted azo dyes with various oligomethylene spacers being synthesized. These spacers play important role in the variation of
The authors declare that there are no competing interests.
This work was supported by FRGS grant obtained from Ministry of Education, Malaysia (no. 130121).