Studies Of Diradicalized Graphene-Like Molecules And Their Properties

The researchers from all over the world have appeared new upsurge in the study on carbonaceous materials since graphene was discovered by Geim et al.in 2004.Graphene has excellent properties in the field of mechanics,electrics,photics and thermotics because of its own special structure.More importantly,graphene has extended ? conjugations which are beneficial to electron transfer and can be used as excellent magnetic materials.However,the reasonable design and application of graphene and its derivative magnetic molecular materials need to be further studied and expanded.There are also some deficiencies in how to regulate the magnetism of graphene magnetic molecules effectively.Designing novel and stable graphene-like organic diradical molecules and exploring their potential magnetic coupling characteristics through comprehensive theoretical calculations will provide strong theoretical basis for the practical application of magnetic materials and promote the development of magnetic material molecules.In order to further expand the research field of graphene-like magnetic materials,we designs four kinds of novel diradical magnetic molecules and their magnetism can be tuned by different ways.The main contributions are as follows:1.Beryllium-doped graphene-like magnetic molecules.A number of studies have shown that small benzene and graphene patches are difficult to generate magnetism.People neeed to further explore simple and effective methods to make small benzene and graphene exhibit significant magnetism.In this work,multi-beryllium-expanded small graphene-like molecules including oligoacenes and graphene patches are computationally designed through introducing two or three Be atoms into the specific benzenoid rings of the graphene-like molecules.As we expected,all these multi-Be-expanded graphene-like molecules exhibit well-defined diradical or polyradical characters,in contrast with the common fact that their parent graphene molecules are closed-shell systems.This work would open a new perspective for the rational design of perfect and stable singlet diradicals or polyradicals with large spin-coupling constants on the basis of small closed-shell graphene-like molecules.2.Core-modified porphyrin-like diradicals with a C=C unit.Porphyrins are similar to graphene and possess extended ? conjugation.The work explores the intramolecular spin interactions of the core-modified porphyrin diradicals with a C=C unit(R-(C=C)and R-(C=C)2+)featuring(C=C)porphyrin and(C=C)porphyrin2+ as the couplers and verdazyl,nitronyl nitroxide,and imino nitroxide as spin sources(R)and the C=C effect.Our results suggest that the core modification with a C=C unit noticeably enhances the spin couplings in R-(C=C)and R-(C=C)2+ compared with R-(Null)with a planar porphine coupler,and R-(C=C)possess mild ferromagnetic couplings but R-(C=C)2+ present strong antiferromagnetic ones,indicating that two-electron redox can switch the magnetisms.The differences in the magnetic properties and coupling magnitudes should be attributed to distinctly different spin-interacting pathways among R-(C=C)and R-(C=C)2+.Besides,the energies of the lowest unoccupied molecular orbitals of the couplers regulate the magnetic couplings,and the linking modes of the radical groups to the couplers also affect the magnetic coupling strengths.This work provides a promising strategy for rational designs of the porphyrin-based diradicaloids and new insights into the spin interaction mechanisms in such diradicaloids which are useful bases for further applications in the future.3.C=C or B-B-cored porphyrin-mimetic graphene patch diradicals.In this work,the cored-modified porphyrin with a C=C or B-B unit is further modified by changing four N atoms into C atoms which can be named the CC-cored molecule and BB-cored molecule,respectively.The spin coupling constants(J)of diradicals were calculated by considering the different linking modes of two nitroxide groups.The results indicate that different core modification considerably affects the J values of such diradicals,and the linking modes can tune the sizes and signs of J.More interestingly,the spin coupling interactions of the CC-cored molecules can also be tuned by stretching the core unit C-C bond.On the other hand,for the BB-cored molecules,two-electron reduction can switch or tune their magnetism from ferromagnetic to antiferromagnetic.The findings about magnetic regulation in these core-modified porphyrin-mimetic graphene patch nitroxide diradicals provide a rational theoretical basis for designing novel building blocks of magnetic functional molecular materials.4.Trinary-bridged bisphenol-like diradicals.Many studies show the biphenyl molecules can be use as couplers to constract diradicals,but the magnetic interactions of biphenyl diradicals can not be tuned,they only show several kinds of magnetic interactions.In this work,biphenyl couplers can be modified by heteroatom or other groups.The intramolecular spin coupling interactions of bisphenol-like trinary-bridged diradicals(nitroxide-(para/meta)phenylene-X-phenylene(para/meta)-nitroxide,X = C=CH2,O,BH,NH and SO2)were explored with an emphasis on the tuning role of the X coupler by density functional theory.The calculated results indicate the linking modes of the radical and X as a middle bridge can mediate spin coupling.All results have been reasonably explained by molecular structures and properties,spin alternation rule,spin density distribution and orbital energy levels.In particular,detailed spin coupling mechanisms are suggested to be cooperative through-space and through-bond pathways with different cooperativity.Clearly,these bisphenol-like molecules possess a greater variety of magnetic properties,which can meet the needs of different practical applications.In summary,the article designs four kinds of graphene-like molecules with diradical characters from more than one angle and explore their magnetic porperties.The work has further expanded the design field of graphene magnetic molecular material.Meanwhile,the study will provide a rational theoretical basis for designing novel building blocks of magnetic functional molecular materials and provide a variety of choices for the application of magnetic materials.