Jun Young Kim

Photoinduced Molecular Re-orientation and Supramolecular Helical Structure Formation in Azobenzene Materials

ABSTRACT Photoinduced chirality in azobenzenes has been investigated. Even in low-molecular weight azobenzenes, photoinduced optical rotation could be observed and the characteristics were similar to that of ever reported in azobenzene side-chain-type polymer. Any relationship between molecular chirality and photoinduced chirality could not be observed in low-molecular weight azobenzenes. Further, very large optical rotation of 41 deg./μm could be observed in an azobenzene copolymer containing large birefringent unit. Dependence of optical rotation on intensity, wavelength and ellipticity of excitation beam were examined. The phenomenon was discussed based on the assumption that photoinduced helical structure was formed by elliptically polarized beam irradiation.

Photoinduced Chirality in an Azobenzene Amorphous Copolymer Bearing Large Birefringent Moiety

A photoresponsive amorphous copolymer that consists of cyanoazobenzene and a large birefringent moiety with extended π-conjugation was recently designed and synthesized. It has been confirmed that this copolymer exhibits a very large optical rotation of 41°/µm under the optimized excitation conditions practically determined within our optical setup, i.e., 457.9 nm, 30 mW and ellipticity=-0.5. The large rotation angle observed could be attributed to the increment of the order parameter of the polymer side chains promoted by the introduction of the extended π-conjugated moiety. Even more, the dependence of optical rotation on beam power, wavelength and ellipticity of the excitation beam has been examined. The phenomenon of photoinduced chirality in an azobenzene amorphous copolymer is discussed and analyzed on the basis of general ellipsometry by solving the transformation matrix of the sample.

Large Photo-Induced Birefringence in Azobenzene Copolymer

ABSTRACT In order to develop the photoresponsible materials for holographic memory, we report an amorphous azobenzene copolymer having large photo-induced birefringence (Δn) and having good thermal stability. We have achieved large photo-induced Δn value of 0.244 in the amorphous film containing azobenzene chromophore at the specific composition ratio. Any relaxation has not been observed even after turn off the writing beam. This large Δn value is attributed to the effective molecular cooperative motion between two chromophores and highly anisotropic molecular structure. Also, the good thermal stability was originated from a rigid rod-like structure of long π-conjugated copolymer segment. From the result, our copolymer can be applied as a new class of material for high performance holographic memory application.

Photoinduced Birefringence and Optical Rotation on Achiral Azobenzene Copolymer

Photoinduced birefringence and photoinduced optical rotation has been investigated on poly{4-[2-(methacryloyloxy)ethyloxy-4′-cyanoazobenzene]-co-4-[[2-(methacryloyloxy) ethyloxy]-2-methyl-4-(phenylazo)]azobenzene} (PCDY50). Originating in a good optical response of cyanoazobenzene side-chain and large birefringence of long π-conjugated side chains, a fairly large photoinduced birefringence (0.28) and photoinduced optical rotation (41°/μm) could be observed. Some applications utilizing these superior photoresponsive properties of PCDY50 have been suggested and demonstrated.

Photoinduced birefringence and cooperative molecular reorientation in azo copolymer: optical characterization for rewritable memory application

In this paper, new azobenzene copolymers (PCDY and PPDY) with large photoinduced birefringence and good long-term stability of a recorded data have been introduced. The largest photoinduced value of 0.289 was obtained on the PCDY50 at 458 nm light irradiation. This value was brought about a result of molecular cooperative reorientation of cyanoazo and bisazobenzene moieties. It should be noted that the PCDY50 exhibited quite stable characteristics on the archival viewpoint. Furthermore, if we can optimize experimental conditions, more than 105 cycles of reversible data storage could be achieved. Making use of these superior characteristics of the PCDY50, an application for rewritable holographic memory and/or other optical addressable devices is anticipated.

Synthesis and Optical Characterization of Photoresponsive Polyester Blend Filmsfor Holographic Data Storage

Two types of new photoresponsive polyester containing 4-cyanoazobenzene (CNAz) and 4-[4-(phenylazo)phenylazo]-o-cresol (DY7) moiety have been synthesized and their optical properties of the two polymer blend were evaluated. The polymers were synthesized from the reaction between azobenzene modified epoxy resin and isophthaloyl chloride. Thin films with good optical quality of each azobenzene modified epoxy resin, its polymer and its polymer blend were obtained by spin coating. The photoinduced birefringence (Δn) measurement was performed with excitation beams of 405 nm, 458 nm, and 488 nm. As a result, with increasing the DY7 content, the Δn was increased due to large intrinsic birefringence of DY7 that originates from extended π-conjugation and highly anisotropic structure of the moiety.

Computer simulation of photoinduced helical structure formation on azobenzene-containing materials

Theoretical models for photoinduced birefringence and chiral structure formation in achiral azobenzene-containing materials were proposed considering phototriggered molecular reorientation via trans-cis-trans photoisomerization cycles of azobenzene. The photoisomerization cycles were expressed by two rate equations of the orientation distributions of trans- and cis-forms. Phototriggered molecular reorientation by illuminating linearly polarized light was verified theoretically. The photoinduced helical structure formation was simualted by elliptically polarized light. The molecular rotation angle was dependent on the sign of the ellipticity. The time evolution of the helical structure formation was consistent with the experimental result that reported by other papers.

Optical characteristics of novel bisazo polymer for rewritable holographic data storage

A novel photoresponsive polymer containing bisazo chromophores have been synthesized for comparative study with monoazo polymer. Since the bisazo structure has an extended Π-conjugation electronic system, it is expected to have large intrinsic molecular birefringence that can realize large macroscopic photoinduced birefringence (ΔnPI) via photoinduced molecular re-orientation process of bisazo molecules. As a result, it was found that the large value of ΔnPI (0.17) could be obtained by using bisazo polymer at 514.5nm excitation with 1.0W/cm2.