| Organic cocrystal engineering has received much attention as an efficient strategy for designing organic multifunctional materials.So far,organic binary cocrystals exhibit excellent optical,electrical and magnetic properties.Inspired by the successful exploration of organic binary cocrystals,the fabrication of higher-order cocrystals,such as ternary cocrystals,have also gained the attention of scientists.The introduction of additional third components and the increase of structural diversity promote the emergence of more novel functions in organic cocrystals.Organic ternary cocrystals not only have superior optoelectronic properties of organic binary cocrystals,but also expand innovative optoelectronic functions,showing great potential in the photoelectric fields of tunable luminescence,optical waveguide,electron transport and external stimulus response.However,compared to the research on the magnetic properties of organic binary cocrystals,there are few studies on the spin or magnetic properties of organic ternary cocrystals.Organic materials exhibit the behavior of unique soft material,so flexible organic semiconductors are also known as strong electron phonon interaction systems.This intrinsic property allows carriers in organic systems to be localized by the lattice,resulting in a unique mode of polaron carrier transport in organic cocrystals,which plays an important role in the photoelectric performance of materials.In addition,electron phonon interactions are not only easily regulated by external stimulis,but also negatively correlated with the number of carbon atoms.With the further exploration of the magnetic origin in organic materials,it has been found that electron phonon coupling plays an indispensable role in the generation and regulation of spin polarization in organic ferromagnets,leading to the emergence of abundant spin properties dependent on spin-lattice interactions,such as spin-Peierls phase transition,magnetoelastic coupling and magnetic anisotropy.In most cases,the molecular weight of the third component in the organic ternary cocrystals is significantly different from that of the initial two molecules.Therefore,when a donor or acceptor molecule is introduced into the organic binary crystal as the third component,it will not only interfere with the self-assembly process of the donor and acceptor,but also change the overall lattice confguration inside the crystal.Thus,the introduction of the third component will most likely modify electron phonon coupling and spin-lattice interactions,thereby further regulate the spin polarization associated with electron-lattice interactions.In order to realize the third component dependent spin effect in organic ternary cocrystals,two steps are needed.The first is to explore the influence mechanism of the third component on the electron-lattice interaction.The second is to realize the regulation of spin polarization or spin lattice interaction related to the third component in the cocrystal.Therefore,based on various types of organic ternary cocrystals prepared by doping or introducing a third component,combined with experimental results and theoretical calculations,this thesis conducted the study of spin-lattice related effects in organic ternary cocrystals.(1)By changing the donor type and the doping ratio of the third element,we prepared different series of ternary charge transfer crystals Donor1-Donor2-Acceptor(D1-D2-A)with TCNB as acceptor to study the third component dependent electron-lattice interactions in these ternary crystals.Firstly,combining the experimental data and theoretical calculation,the effects of the competition between two charge transfer interactions on the band structure,electronic states and spin properties are studied in the ternary cocrystals.With the doping of the third component D2,the charge transfer interaction between D1-A and D2-A is obviously competitive.And the third component related competition can be regulated by incident light field and temperature.Furthermore,under the stimuli of external magnetic field,Dx-A with weaker charge transfer interaction shows a better tunability of the related physical properties.In addition,by measuring the electron phonon coupling strengths of organic ternary cocrystals with different doping ratios,it was found that the electron-lattice interaction is significantly related to the third component doping ratio.The electron phonon coupling strength decreases with the increase of the third component doping ratio,and its electron phonon coupling strength is also regulated by external light intensity and temperature,thereby further affecting the charge dissociation.These results provide more detailed information for understanding the spin and photophysical phenomena of organic ternary crystals.(2)Based on the conclusions drawn from the first work,in the second work,we studied the spin polarization effect in organic ternary cocrystals by doping the third component purposely.Through introducing a third component as inducer,the self-assembly process of donor pyrene and acceptor TCNQ was regulated,then two organic allotropic charge transfer cocrystals C1 and C2 with different space group,lattice parameters and molecular configuration are fabricated.The experimental and computational results of lattice dynamics show that under the stimulation of the third element,the lattice vibrations and total electron phonon coupling of C1 and C2 exhibit significant differences,and compared to the C2 configuration with weak electron phonon coupling,the C1 configuration with strong electron phonon coupling has a smaller spin polarization,realizing the indirect control of the spin-lattice interaction by the third element.In addition,due to the significant differences in spin-lattice coupling,there are obvious differences in the degree of regulation of magnetic fields on the transmittance and fluorescence lifetime of C1 and C2 crystals.By lowering the temperature or applying electric field,the electron phonon coupling coefficient tends to decrease,where the electron phonon coupling dependence of magnetical dielectric coupling present pronounced differences for the C1 and C2 crystals.This work emphasizes the influence of the third component doping on spin polarization and spin-lattice interaction in organic ternary cocrystals,laying a foundation for the further research about spin-lattice coupling dependent novel spin properties in organic ternary cocrystals.(3)We successfully fabricated three organic full component ternary charge transfer crystals by introducing a third component into the unit cell of organic binary cocrystals,breaking through the difficult problem about the growth of organic ternary cocrystals.We mainly studied the third component dependent magnetic anisotropy,phase transition and multiferroics magnetoelectric coupling effects.Utlizing single crystal XRD,the arrangement of three different molecules in crystal was analyzed.As the third donor molecule was introduced into the binary crystal,the lattice configuration changed and the localization degree of holes became weak,thereby the spin polarization intensity of the ternary cocrystals were significant regulated.More importantly,the third component induces dimerization between adjacent donor and acceptor,resulting in lattice symmetry breaking,where a nonpolar to polar phase transition is ensuing to lead to a dipolar polarization.Magnetic field can effectively control the dipole polarization in polar charge transfer crystals,resulting in magnetoelectric coupling effects.In addition,the introduction of new donors may lead to the rearrangement of molecular configurations,thereby changing the electron phonon interaction.As a result,anisotropic magnetism is observed due to the anisotropic electron phonon coupling in ternary crystals.Overall,the coexistence of dipole polarization and spin polarization in organic ternary crystals provides a potential path for the design of organic multiferrous materials,indicating that the research on the spin properties of organic ternary cocrystals has infinite potential. |
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