Molecular weight (MW) control is always an important issue in numerous cases of polymerization and oligomerization. For polymerization, MW control is generally achieved by ways of controlling the processes of mainchain initiation, transfer and termination. For oligomerization, in contrast, it is basically accomplished by the step-by-step expansion of the repeating unit in backbone (Chem. Rev. 2011, 111, 2321; J. Am. Chem. Soc. 2013, 135, 19095). As compared with these traditional solution-based synthesis, topochemistry can effectively work without additional reagents and solvation requirements (Acc. Chem. Res. 2008, 41, 1215; Chem. Soc. Rev. 2009, 38, 1958), hence it is attractive in various fields of modern chemistry. Although topochemical reactions can be convenient and straightforward, they largely rely on preorganization of the reactive components to facilitate bond-making and bond-breaking through minimal atom displacement. In this way, scientists developed different ways of controlling the alignment of reactants for pursuing high reaction rate, high yield or diverse conversions (Science 2006, 312, 1030; Chem. Soc. Rev. 2013, 42, 950, etc.). However, to the best of our knowledge, MW control in topochemical polymerization or oligomerization remains out of precise control, probably due to the lack of smart and optimized intermolecular alignment fashions.
Zhu’s group aimed at seeking the way to control the topochemical photocrosslinking degree for obtaining a series of uniform oligomeric π-functional species, since difference in repeating-unit of yielded π-structured oligomers can normally connect with distinct functionality-oriented applications, especially for those visualized optoelectronic events. (Chem. Rev. 2000, 100, 2537; Chem. Sci. 2016, 7, 2058). To address the above-mentioned issues, they proposed the strategy in the work with the following contributions:
1) They presented a rational design of a diphenyldiacetylene derivative DPDA containing two quaternized imidazole, which has a good solubility in aqueous media and can build electrostatic interaction with negatively charged species or templates. Well-selected biomacromolecular templates, namely, BSA (Albumin from bovine serum), DNA (Calf thymus) and HS (Heparin sodium), were employed, and their binding constant exhibited a progressive order of magnitude towards DPDA. On this basis, MW control for uniquely forming corresponding dimeric and trimeric oligodiacetylenes can be successfully achieved upon photoirradiation with the template optimized from the perspective of adjustable dynamic equilibrium.
2) As a tunable molecular photoluminescence property has become crucial in diverse needs of bioimaging and labelling (J. Am. Chem. Soc. 2013, 135, 5175; Chem. Commun. 2017, 53, 10765). The formed dimeric and trimeric oligodiacetylenes, interestingly, exhibit respectively blue and yellow fluorescence, and therefore can be applied into selective and multi-channel bioimaging with good biocompatibility on account of their biomacromolecular templates, featuring the merits of obtaining species with repeating-unit difference for material applications.
The related paper has been published in Macromolecules, with Dr. Xiaoyong Jia, a postdoc in the group as the first author. See details:
Xiaoyong Jia, Mingjie Zhu, Qiao Bian, Bingbing Yue, Yaping Zhuang, Bin Wu, Lin Yu, Jiandong Ding, Junji Zhang, Liangliang Zhu*, Precisely Controlling Dimerization and Trimerization in Topochemical Reaction Templated by Biomacromolecules, Macromolecules 2018. DOI: 10.1021/acs.macromol.8b01824
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