厦门大学学报（自然科学版）2025，Vol.64Issue(5)：775-781,7.DOI:10.6043/j.issn.0438-0479.202404023
手性共轭纳米柱自由基的合成与表征
Synthesis and characterization of chiral conjugataed nanopillar radicals
摘要
Abstract
[Objective]Chiral organic radicals,which combine molecular chirality with open-shell-lay er properties,are endowed with small highest occupied molecular orbit(HOMO)and lowest unoccupied molecular orbit(LUMO)energy levels,strong electronic polarizabilities,and suitable electron spin relaxation times,making them ideal systems for studying electron spin-chiral interactions and for developing multifunctional materials.However,most chiral radicals tend to be poorly stabilized,easily quenched,and difficult to separate into chiral isomers.Thus,the preparation of stable chiral radicals remains a major challenge.Herein,chiral π-conjugated nanopillar anions A4-·/B4-·and dianions A42-·/B42-·with naphthodithiophenediimide(NDTI)as the unit were synthesized to construct stable chiral radicals.[Methods]The chiral π-conjugated nanopillar B4 was subjected to square wave voltammetry test to evaluate its electron gaining ability.Cobaltocene was chosen as the reducing reagent,and the A4 or B4 dichloromethane solution was titrated using cobaltocene solution to obtain pure anion A 4-·/B4-·and dianion A42-·/B42-·solution by observing the changes in the ultraviolet-visible-near infrared(UV-Vis-NIR)absorption spectra after the addition of different equivalents of cobaltocene.A4-·/B4-·and A42-·/B42-·were characterized using electron paramagnetic resonance(EPR)and UV-Vis-NIR circular dichroism spectroscopy,and the electron spin densities of both were calculated at the B3LYP-D3/6-31+G(d)level.[Results]Square-wave voltammetry tests showed that the B4 molecule exhibited a low reduction potential,with the first and second reduction potentials at-0.09 and-0.20 V,respectively,reflecting the strong electron deficiency property of B4,which is favorable for redox reaction with cobaltocene.The UV-VIS-NIR absorption spectra showed that both B4-·and B42-·embodied the near-infrared absorption property,in which the absorption spectrum of B42-·produced a characteristic two-photon absorption peak of the open-shell singlet ground state.Variable-temperature(VT)EPR spectrum confirmed that B42-·was an open-shell singlet ground state diradical with a singlet-triplet energy gap(△ES-T)of-1.11 kJ/mol.In addition,UV-Vis-NIR circular dichroism spectra combined with spin density maps revealed the near-infrared circular dichroism of A4-·/B4-·and A42-·/B42-·,which could be attributed to the interaction of unpaired electrons with chirality.The large steric hindrance effect led to the inability of the NDTI units to rotate freely,which enhanced the π-elect ron delocalization between structural units.The unpaired electrons were predominantly distributed on the π-conjugated nanopillar backbone,surrounded by chiral thiophene groups.The chiral-induced effect led to spin polarization of the unpaired electrons.When it received the right energy,the system could produce locally excited polarized electrons,and the difference in the absorption of left and right circularly polarized light by these excited polarized electrons finally produced the near-infrared circular dichroism signal.[Conclusion]In this study,chiral radical A4-·/B4-·and diradical A42-·/B42-·were synthesized by chemical reduction,demonstrating that π-conjugated nanopillar could sufficiently delocalize unpaired electrons to stabilize open-shell layer radical or diradical.A4 2-·and B42-·showed potential applications in the field of organic semiconductors due to its extremely low△ES-T and unique nanopillar structure.In addition,changing the interaction of the unpaired electrons and chiral groups could modulate the resulting chiral-induced effect,leading to the near-infrared circularly polarized characteristic absorption of radical or biradical.This work presents a new method for the development of chiral organic biradicals that combine high stability with a low △ES-T.关键词
有机自由基/手性/萘并二噻吩二酰亚胺/共轭纳米柱Key words
organic radical/chirality/naphthodithiophenediimide/conjugataed nanopillar分类
化学化工引用本文复制引用
潘元丰,林建斌..手性共轭纳米柱自由基的合成与表征[J].厦门大学学报（自然科学版）,2025,64(5):775-781,7.基金项目
国家自然科学基金(22071208,22271239) （22071208,22271239）
