Tetrabenzo-chichibabin’s Hydrocarbons:Substituent Effects And Unusual Opto-electronmagnetic Properties

Chichibabin’s hydrocarbons represent a typical type of diradicals,which push the significant development in the field of open-shell molecules.They play a crucial role in understanding the nature of chemical bonds and the underlying physicochemical phenomena ofπ-conjugated systems.Their unique optoelectronic physics has received great attention in the field of materials science,and has potential applications in near-infrared dyes,organic field-effect transistors and nonlinear optical materials.Due to the contribution of the biradical resonance,they usually exhibit extremely activitity.Thus,they are quite unstable,even at the room temperature.To stabilize them,the thermodynamic and dynamic method are important means,including electron delocalization and active site protection.However,their substituent effects is rarely reported.In this work,we have design two precursors,which can proceed the reactions by either the Suzuki coupling or radical resonance.The target molecules are the tetrabenzo-Chichibabin’s hydrocarbons.In these cases,different substituents are incorporated into the reaction precusors.Then we can study the substituent effect in both reaction,as well as the final structural analysis.We have also investigated TBCs’properties,and found that the compound TBC-4DMA@2Cl exhibits unusual thermochromic and thermomagnetic behaviours.Based on these results,we have proposed that double-fused Chichibabin hydrocarbon should be interesting precursor if hetero atoms（i.g.,sulfur）are fused at peri-position.After reduction of such precursor,a new class of tetraradical cation could generate since positive sulfur should be used as effective unpair electron acceptors.The main content of this article is as follows:（1）We designed two precursors bearing different substituents,which are arranged the central biphenyl group in butterfly-like and orthogonal configuration,respectively.The former performed Suzuki coupling reaction to afford quinoidal tetrabenzo-Chichibabin’s hydrocarbons,while the later resonace into the biradic al forms after reduction with SnCl₂.In these cases,substituents effect would be investigated,for both radical process and structure influence.Surprisingly,the strong electron-donating group（dimethyl amine）makes the molecular system generate a cationic salt with similar structure of cyanine dye.（2）We further explored the physical properties of TBCs,and found that the-CF₃,and-OMe groups have a less influence on the ground state electronic structure,as well as opoeletronic properties.Their ground state electronic structures are closed-shell quinoid-like configuration.Interestingly,the unexpected cyanine-like product TBC-4DMA@2Cl is a potential magnetic and chromic switch upon thermal excitation due to thermally access to meta-stable biradical form.（3）Encouraged by the above results,we we designed a double-fused Chichibabin’s hydrocarbon derivative,which consist of a perylen core and peri-fused four sulfur at the terminals.After reduction with one-electron oxidant,a new class of cation could be generated,which should possess tetraradical character.This paln aims to provide a new idea for polyradicaloid system.