p-Methoxy Azobenzene Terpolymer as a Promising Energy-Storage Liquid Crystal System

Abstract

Light-responsive materials capable of undergoing photoinduced molecular transformation are excellent candidates for energy storage. Herein, we report a promising new liquid crystalline terpolymer that is capable of trapping the absorbed photon energy upon exposure to UV light through trans → cis isomerization and molecular aggregation. MeOAzB-T (contains pmethoxyazobenzene, 2-acrylamido-2-methyl-1-propanesulfonic acid, and methyl(methacrylate) monomeric units) shows a trans ← cis normal thermal recovery in solution (THF) after UV exposure, whereas in the glassy state (at 22 °C) and smectic phase (at 75 °C), the recovery process indicates an unusual increase in absorbance of the trans isomer. Surprisingly, when the smectic phase was cooled down to the glassy state while maintaining UV exposure, the increase in absorbance of the trans isomer was maintained at the same level in the dark (monitored for 20 days) until the sample was heated to 75 °C and then cooled to 22 °C in which a full recovery was achieved. Enhancement of H-and Jaggregations of the trans-MeOAzB units was found to be responsible for the absorbance increase. Both forms of aggregation have absorbance signatures and were reproduced by time-dependent density functional theory (TD-DFT). A long lifetime component was detected in the femtosecond transient absorption (TA) spectra in thin films (215 ps in the glass state and 97 ps in the smectic phase) and was assigned to a long-lived intermediate state as a result of aggregation. The stability of the excited state leads to more aggregation as a consequence of the larger dipole moment, compared to the ground state, which is manifested in the TD-DFT calculations as an increase in electron density at the central azo bond. The current results suggest that aggregation after UV irradiation can be maintained for a long time at room temperature and can be relaxed to the original configuration by heating above the glass transition, showing the suitability of MeOAzB-T as a solar thermal fuel.

Light-responsive bent-core liquid crystals as candidates for energy conversion and storage

“…Even though azobenzenes have been studied for several decades [5][6][7], they continue to attract interest due to their potential to promote long-range macroscopic changes induced by short-range molecular modifications. [8][9][10][11][12] Bent-core liquid crystals, BCLCs, exhibit anti-ferroelectric and ferroelectric behaviour with high figures of merit, which can be useful for energy storage applications. BCLCs can form columnar (Col, former B 1 ), polar smectic C (SmCP, former B 2 ), twist grain boundary dark conglomerate (DC) or helical nanofilament (HNF, former B 4 ) phases among others [13][14][15][16][17][18][19][20].…”

“…Even though azobenzenes have been studied for several decades, 5–7 they continue to attract interest due to their potential to promote long-range macroscopic changes induced by short-range molecular modifications. 8–12…”

Solar–Thermal Fuels and the Role of Carbon Nanomaterials: A Perspective with Emphasis on the Azobenzene System

“…Therefore, the design of STFs with expanded capacity of absorption and discharging within the full solar spectrum is of strong interest. In this sense, a coupling of UV-sensitive azopolymers with visible-light-sensitive azopolymer was exploited by Saydjari et al A similar approach to UV-sensitive azopolymers relying on a p -methoxy AB terpolymer was recently proposed by Ibrahim et al Other interesting possibility is the expansion of the isomerization window to the near-infrared region, which was exploited in different works. , …”

“…Therefore, the design of STFs with expanded capacity of absorption and discharging within the full solar spectrum is of strong interest. In this sense, a coupling of UV-sensitive azopolymers with visible-light-sensitive azopolymer was exploited by Saydjari et al 164 A similar approach to UVsensitive azopolymers relying on a p-methoxy AB terpolymer was recently proposed by Ibrahim et al 165 Other interesting possibility is the expansion of the isomerization window to the near-infrared region, which was exploited in different works. 3,166 Nonetheless, these hybrid STFs still face serious difficulties in combining their new properties with high photochromic reaction yields (i.e., full conversion of trans-AB into cis-AB, upon irradiation) and a narrow UV absorption maximum, failing to capture most of the solar spectrum.…”

Exciton states of azobenzene aggregates: A first-principles study

“…Shifting between the isomers with light enables various transformations and control over numerous properties of systems ranging from macromolecules 1-3 through interfaces 4,5 to solids. [6][7][8] In (soft) condensed matter systems, such as azobenzene-containing self-assembled monolayers (SAMs), 9,10 micelles, [11][12][13] , liquid crystals 14 or crystals, 15 azobenzene units are, in general, coupled to each other. This coupling manifests itself in spectral changes with respect to the corresponding "monomer" case, e.g.…”