Effect Of Branched Structure On Organic Photorefractive Performance

Photorefractive effect is a nonlinear optical phenomenon that can change the internal structure of the material due to light response and eventually produce refractive index modulation.It has been applied to many aspects,such as three-dimensional holographic storage,biomedical imaging,data storage,signal amplification,and so on.Organic photorefractive materials have received much attention due to their ease of design and excellent optical properties.Our group has designed and synthesized a series of organic all-optical photorefractive materials in the past.However,the relationship between the material structure and organic photorefractive properties has not been fully explored.In addition,since most materials with good photorefractive properties require pre-polarization or external electric field,system exploration of all-optical photorefractive materials is of great significance.The main purpose of this paper is to systematically explore the relationship between the branched structure and all-optical photorefractive properties,the internal and external factors during the fabrication of photorefractive devices.Through which provides theoretical basis and different ideas for designing organic all-optical photorefractive materials and improving device performance.In the first part of this paper,the two-wave coupling experimental setup was built for organic photorefractive characterization.Then the applicable calibration in different optical power ranges and the calculation formula of gain coefficient was deduced.On the other hand,the method of fabricating devices has also been demarcated which lays the foundation for the following work.The second part of this paper talks about linear polymer（LP）and hyperbranched polymer（HP）with triphenylamine as the main part,and proved that the hyperbranched structure can improve the photorefractive properties of materials.Under the same condition,HP’s gain coefficient(62.50cm^-1)was 1.7 times as the value of LP in all-optical photorefractive performance.In the third part of this paper,a series of hyper-structured macromolecules（HSM）with one generation of dendritic morphology were studied.Calix[4]resorcinarene（CRA）was used as a core and azobenzene/methane groups were used as NLO chromophores,respectively.The photorefractive properties and the effects of chromophore’s structure and concentration were explored.Experiments showed that all the samples had satisfied all-optical photorefractive properties,which proved that the dendritic structure plays an effective role.Among them,the two-wave coupling gain coefficient of the device formed by CRA-CSN₇₅-Cz₂₅ reached 80.11cm^-1.In the fourth part,combining the two major structure mentioned above,a dendronized hyperbranched polymer with chromophores at the periphery was designed,and used as a research object to explore the effect of this unique three-dimensional structure on the photorefractive effect.The test proved that it had all-optical photorefractive properties(Γ=44.11cm^-1),and its sensitivity to low external electric field was greatly improved than that of other branched structures.Under low electric field of 10.00V/μm,the value ofΓwas increased about 7.2 times.In the fifth part,the hyper-structured macromolecules with simple structure were chosen to add carbon materials for tests.The photorefractive devices were optimized and adjusted by exploring the doping order and proportion.When adding0.5%wt of poly-carbon,the two-wavelength coupling gain coefficient of the device reached 117.25cm^-1,which achieved the 46%increase compared to the un-doped one.