摘要
不含普通发光单元的非典型生色团发光化合物因其基础研究重要性和广泛的应用前景引起了人们的极大兴趣.其中许多化合物还具有独特的聚集诱导发光(Aggregation-induced emission,AIE)特性.然而其发光机理仍然存在争议.在此前的研究中,提出了簇聚诱导发光(clustering-triggered emission,CTE)机理,即非典型生色团的簇聚和电子共享来解释这些体系的发光和AIE现象.为进一步验证这一假说,设计合成了不含传统生色团的聚甲基丙烯酸(N-羟基琥珀酰亚胺)酯(PNHSMA).其稀溶液基本不发光,但浓溶液,纳米聚集体,固体粉末均发射蓝光,呈现出AIE性质.通过与其单体甲基丙烯酸(N-羟基琥珀酰亚胺)酯(NHSMA)的发光行为对比及单体单晶结构解析,利用CTE机理很好地解释了其光物理行为.
Nonconventional luminogens without classic aromatic or conjugated structures are attracting increasing interests owing to their fundamental importance and promising applications in diverse areas. Many of them even exhibit unique aggregation-induced emission （AIE） characteristics. The emission mechanism, however, remains under debate. Previously, we proposed the clustering-triggered emission （CTE） mechanism, namely the clustering of nonconventional chromophores and subsequent electron overlap to rationalize the emission behaviors of such luminogens. To further our understanding, herein, we designed and synthesized poly（N-hydroxysuccinimide methacrylate） （PNHSMA） without any aromatic structures, which was obtained by the radical polymerization of N-hydroxysuccinimide methacrylate （NHSMA） monomer in toluene at 65℃ utilizing azobisisobutyronitrile （AIBN） as initiator. And NHSMA was prepared through the elimination between N-hydroxysuccinimide （NHS） and methacryloyl chloride in the presence of triethylamine （Et3N）. It is found that PNHSMA is virtually nonluminescent in dilute solutions （40.4 mg.mL-1） even at 77 K, but gets emissive in concentrated solutions （e.g. 40 mg.mL-1） with photoluminescence （PL） maxima at 434 and 485 nm at room temperature. Moreover, its solid powders emit intense blue light with multiple PL peaks upon UV irradiation, indicating its AlE nature and the formation of varying emission species. Further PL measurement of PNHSMA in dimethylformide （DMF） and DMF/acetone （good solvent/nonsolvent） mixtures duly verifies its AlE feature. Meanwhile, NHSMA monomer shows similar emission behaviors to those of PNHSMA, demonstrating concentration enhanced emission and AlE characteristics. In light of above results, it is assumed that NHSMA and its polymeric counterpart PNHSMA may share the similar emission mechanism. Single crystal structure of NHSMA reveals the conjugation of imide group and 3D intermolecular interactions of C=O…C=O （n-n, 3.072 A）, C=O…H-C （2.651, 2.642 A） and C=O…C--H （3.099 A）. The emission of PNHSMA and NHSMA in concentrated solutions and solid states is thus ascribed to the clustering of imide and ester groups, which results in electronic interactions. The overlap of π and lone pair （n） electrons among C = O, N and O units, together with effective intermolecutar interactions in the solid powders extend the conjugation and rigidify the molecular conformations, thus leading to boosted emissions. Such CTE mechanism might be well extended to other nonconventional systems and should be inspiring for the rational design of novel luminogens.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2016年第11期935-941,共7页
Acta Chimica Sinica
基金
国家自然科学基金(No.51473092)
上海市青年科技启明星计划(No.15QA1402500)资助~~
