Funada Tomohito, Hirose Takuya, Tamai Naoto, Yao Hiroshi
Graduate School of Material Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan.
Phys Chem Chem Phys. 2015 Apr 28;17(16):11006-13. doi: 10.1039/c5cp00031a.
In tracing the biological processes using fluorescent probes, it is desirable to shift the excitation/emission energy to a far-red/near-infrared (FR/NIR) region. In this study, we successfully synthesize FR fluorescent organic nanoparticles via ion-association between the malachite green (MG) cations and tetrakis(4-fluorophenyl)borate (TFPB) anions in the presence of a neutral stabilizing polymer. Binding of MG with TFPB results in the prominent appearance of an absorption band that can be assigned to an H-aggregate of MG. The fluorescence intensity as well as the fluorescence lifetime shows a significant increase with a decrease in the nanoparticle size. Since the MG dye is known as a local viscosity or environmental rigidity probe showing a rotational friction dependence of the excited state lifetime, we find that the rigidity of the organic nanoparticle is strongly size-dependent; that is, the smaller the size of the nanoparticle, the greater the rigidity of the nanoparticle. We also reveal that surface regions of the ion-based organic nanoparticles are more rigid than inner regions. The presence of H-aggregates that are almost non-fluorescent is the major origin of aggregation-caused quenching (ACQ) and still avoids the enhancement of the fluorescence quantum yield of the MG nanoparticles, so we develop a new approach to prevent H-aggregation inside the nanoparticle by incorporating photochemically inert, bulky phosphonium cations, which results in a 430-fold enhancement of its fluorescence yield. We believe that such a methodology will open up an avenue in the development of new types of fluorescent nanomaterials for many applications.
在使用荧光探针追踪生物过程时，希望将激发/发射能量转移到远红/近红外（FR/NIR）区域。在本研究中，我们通过孔雀石绿（MG）阳离子与四（4-氟苯基）硼酸根（TFPB）阴离子在中性稳定聚合物存在下的离子缔合，成功合成了FR荧光有机纳米颗粒。MG与TFPB的结合导致出现一个可归属于MG的H-聚集体的吸收带。随着纳米颗粒尺寸的减小，荧光强度和荧光寿命均显著增加。由于MG染料是一种局部粘度或环境刚性探针，其激发态寿命显示出旋转摩擦依赖性，我们发现有机纳米颗粒的刚性强烈依赖于尺寸；也就是说，纳米颗粒尺寸越小，其刚性越大。我们还揭示了离子基有机纳米颗粒的表面区域比内部区域更刚性。几乎无荧光的H-聚集体的存在是聚集诱导猝灭（ACQ）的主要来源，并且仍然避免了MG纳米颗粒荧光量子产率的提高，因此我们开发了一种新方法，通过引入光化学惰性的大体积鏻阳离子来防止纳米颗粒内部的H-聚集，这导致其荧光产率提高了430倍。我们相信，这种方法将为开发用于许多应用的新型荧光纳米材料开辟一条道路。
