Photoinduced phase transitions

Abstract

Employing actinic light to alter/stabilise a particular thermodynamic phase via the photo-isomerisation of the constituent molecules is an interesting tool to investigate soft matter from a new dimension. This article focuses on our recent results on several aspects of these non-equilibrium phase transitions, which are isothermal in nature. We specifically discuss (i) the influence of different parameters, such as confinement, applied electric field, pressure etc., on the dynamics associated with both the photochemical transition driving the equilibrium nematic to the nonequilibrium isotropic phase and the thermal back relaxation recovering the nematic phase, (ii) unique light-driven disorder-order transition in a reentrant system, (iii) dynamic self-assembly of the smectic A phase, which is stabilised only in the presence of actinic light, (iv) novel temperature-intensity phase diagrams and an example of primary and secondary photo-ferroelectric effects in an antiferroelectric smectic C system. These results highlight the fact that the actinic light can be used as a new tool to study phase transitions and the associated critical phenomena that could also bring about effects that are not seen in equilibrium situations.

Photoresponsive behavior of hydrophilic/hydrophobic-based novel azobenzene mesogens: synthesis, characterization and their application in optical storage devices

“…(1) (n ¼ 7) yield: 71.5%. 1 H NMR (400 MHz, CDCl 3 ) d/ppm 7.38-7.32 (m, 2H), 7.13 (s, 1H), 6.88-6.80 (m, 2H), 3.96-3.88 3.1.2 General synthetic procedure for 4-alkyloxyanilines (4)(5)(6). To a 250 mL round-bottom ask containing the corresponding 4-acetamidophenoxyalkanes (1-3), sodium hydroxide pellets in ethanol were added.…”

“…Excess 1,6-dibromohexane was removed by washing the residue with n-hexane and the products were recrystallized from methanol to yield compounds 10-12. 6.98 (dd, J ¼ 9.0, 1.0 Hz, 4H), 4.02 (td, J ¼ 6.5, microscopy (POM) and differential scanning calorimetry (DSC). For polarizing microscopy, a Linkam hot stage and temperature observation under polarized light of an Olympus BX 51 polarizing optical microscope were used.…”

“…[1][2][3][4][5] Organic photochromic compounds are used to evaluate the photoinduced behaviour of optical storage devices. 6,7 This process arises from the reversible photoinduced isomerization of a photochromic group such as azobenzene. The azobenzene chromophore is a good candidate for storing data optically due to its photosensitivity and good photoisomerization properties.…”

Photocontrolled Phase Transitions and Reflection Behaviors of Smectic Liquid Crystals by a Chiral Azobenzene

“…A small amount of azobenzene chromophores could be used as guest molecules to affect the structures and properties of host LCs, due to their trans-to-cis photoisomerization. [10] The trans isomers stabilize the phase structure of LCs, while the cis isomers tend to destabilize the phase structure of the mixture because of their bent shape. [11][12][13][14] As such, it is not unexpected that plenty of work has focused on controlling the optical properties of nematic and cholesteric LCs doped with azobenzene chromophores.…”

Photoinduzierte Stimulierung und Unterdrückung von Phasenübergängen in Flüssigkristallen

“…Auf die Temperatur reagierende LCs werden hierbei als thermotrop und konzentrationsempfindliche als lyotrop bezeichnet. [1] Vor einiger Zeit kam als neuer Parameter das Licht hinzu, [2] und LCPhasen, die durch Licht induziert werden, werden phototrop genannt. [3] Die Mçglichkeit, durch Licht die konstituierenden Moleküle zu isomerisieren und somit die thermodynamische Phase entweder zu verändern oder zu stabilisieren, stellt für die Festkçrperforschung eine interessante neue Dimension dar.…”