Two bromobenzene-capped quinoline-based oligoamide foldamers with different lengths and different side chains are designed and synthesized. The compounds have been characterized by UV-Vis, fluorescence spectra, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results show that the side chains have no effects on the morphology of the aggregated state and the different aggregated morphologies have great influence on the fluorescence intensity. The photoluminescence behavior of the compounds in THF-H2O binary solvent system and films has been studied, and these compounds display aggregation-induced emissions (AIE). They hardly emit light in the solution state, whereas the photoluminescence intensity in the solid state is several dozen times higher than that in THF-H2O binary solvent system. This AIE phenomenon is caused by the stable helical structure of foldamers which restricts the intramolecular random rotation of single bonds and intermolecular closest packing. Moreover, the AIE effect of the foldamers is strongly affected by solvents.
[1] Zhao Z, Chen S, Chan C Y, et al. A facile and versatile approach to efficient luminescent materials for applications in organic light-emitting diodes[J]. Chem Asian J, 2012, 7(3):484-488.
[2] Shan X C, Zhang H B, Chen L, et al. Multistimuli-responsive luminescent material reversible switching colors via temperature and mechanical force[J]. Cryst Growth Des, 2013, 13(4):1 377-1 381.
[3] Kim T I, Jin H, Bae J, et al. Excimer emission-based fluorescent probe targeting caspase-3[J]. Anal Chem, 2017, 89(19):10 565-10 569.
[4] Liu J, Ren J, Bao X J, et al. pH-Switchable fluorescent probe for spatially-confined visualization of intracellular hydrogen peroxide[J]. Anal Chem, 2016, 88(11):5 865-5 870.
[5] Deng H P, Su Y, Hu M, et al. Multicolor fluorescent polymers inspired from green fluorescent protein[J]. Macromolecules, 2015, 48(16):5 969-5 979.
[6] Ma X F, Sun R, Cheng J Y, et al. Fluorescence aggregation-caused quenching versus aggregation-induced emission:a visual teaching technology for undergraduate chemistry students[J]. J Chem Educ, 2015, 93(2):345-350.
[7] Luo J D, Qiu C S, Kwok H, et al. Aggregation induced emission of 1-methyl-1,2,3,4,5-pentaphenylsilole[J]. Chem Commun, 2001, 381(18):1 740-1 741.
[8] Chen J W, Charles C W, Jacky W Y, et al. Synthesis, light emission, nanoaggregation, and restricted intramolecular rotation of 1,1-substituted 2,3,4,5-tetraphenylsiloles[J]. Chem Mater, 2003, 15(7):1 535-1 546.
[9] 张双,秦安军,孙景志,等. 聚集诱导发光机理研究[J]. 化学进展, 2011, 23(4):621-636.
[10] Fan X, Sun J, Wang F, et al. Photoluminescence and electroluminescence of hexaphenylsilole are enhanced by pressurization in the solid state[J]. Chem Commun, 2008, (26):2 989-2 991.
[11] Ren Y, Jacky W Y L, Dong Y Q, et al. Enhanced emission efficiency and excited state lifetime due to restricted intramolecular motion in silole aggregates[J]. J Phys Chem B, 2005, 109(3):1 135-1 140.
[12] Xie Z Q, Yang B, Xie W J, et al. A class of nonplanar conjugated compounds with aggregation-induced emission:structural and optical properties of 2,5-diphenyl-1,4-distyrylbenzene derivatives with all cis double bonds[J]. J Phys Chem B, 2006, 110(42):20 993-21 000.
[13] Zhang G, Lu J, Fraser C L. Mechanochromic lum-inescence quenching:force-enhanced singlet-to-triplet intersystem crossing for iodide-substituted difluoroboron-dibenzoylmethane-dodecane in the solid state[J]. Inorg Chem, 2010, 49(23):10 747-10 749.
[14] Braye E H, Hubel W, Caplier I. New unsaturated heterocyclic systems[J]. J Am Chem Soc, 1961, 83(21):4 406-4 413.
[15] Luo J, Song K, Gu F L, et al. Switching of non-helical overcrowded tetrabenzoheptafulvalene derivatives[J]. Chem Sci, 2011, 2(10):2 029-2 034.
[16] Becker H D, Sandros K, Skelton B W, et al. Relationship between fluorescence and molecular geometry. proximity effects in fluorescence quenching by the anthrone-anthracene interaction[J]. J Phys Chem B, 1981, 85(20):2 927-2 930.
[17] Nyakatura E K, Rezaei A R, Mortier J, et al. An unusual interstrand H-bond stabilizes the heteroassembly of helical alphabetagamma-chimeras with natural peptides[J]. ACS Chem Biol, 2014, 9(3):613-616.
[18] Montalvo G L, Zhang Y, Young T M, et al. De novo design of self-assembling foldamers that inhibit heparin-protein interactions[J]. ACS Chem Biol, 2014, 9(4):967-975.
[19] Qi T, Deschrijver T, Huc I. Large-scale and chromatography-free synthesis of an octameric quinoline-based aromatic amide helical foldamer[J]. Nat Protoc, 2013, 8(4):693-708.
[20] Chen Z, Urban N D, Gao Y, et al. Covalent reinforcement of hydrogen-bonded discs into stably folded helical structures[J]. Org Lett, 2011, 13(15):4 008-4 011.
[21] Dolain C, Jiang H, Leger J M, et al. Chiral induction in quinoline-derived oligoamide foldamers:assignment of helical handedness and role of steric effects[J]. J Am Chem Soc, 2005, 127(37):12 943-12 951.
[22] Jiang H, Leger J M, Dolain C, et al. Aromatic delta-peptides:design, synthesis and structural studies of helical, quinoline-derived oligoamide foldamers[J]. Tetrahedron, 2003, 59(42):8 365-8 374.
