Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
J Phys Chem B. 2010 Oct 21;114(41):13159-66. doi: 10.1021/jp106689w.
Ultrafast fluorescence resonance energy transfer (FRET) in a mixed micelle containing a room-temperature ionic liquid (RTIL) is studied by picosecond and femtosecond emission spectroscopy. The mixed micelle consists of a triblock copolymer, (PEO)(20)-(PPO)(70)-(PEO)(20) (Pluronic P123), and a RTIL, 1-pentyl-3-methyl-imidazolium tetra-flouroborate, ([pmim][BF(4)]) or 1-pentyl-3-methyl-imidazolium bromide ([pmim][Br]). Coumarin 480 (C480) is used as the donor, and the acceptor is rhodamine 6G (R6G). Multiple time scales of FRET were detected-an ultrashort component of 1-3 ps and two relatively long components (300-400 ps and 2500-3500 ps). The different time scales are attributed to different donor-acceptor distances. It is proposed that the ionic acceptor (R6G) is localized in the polar corona region of the mixed micelle, while the neutral donor (C480) is distributed over both corona and hydrophobic core regions. The ultrafast (1-3 ps) components are assigned to FRET at a close contact of donor and acceptor. This occurs for the donor in the polar corona region in close proximity of the acceptor. The longer components (300-400 ps and 2500-3500 ps) arise from long-distance FRET from the donor at the core and the acceptor at the corona region. The relative contribution of the ultrafast component of FRET (∼3 ps) increases from 5% at λ(ex) = 375 nm to 30% at λ(ex) = 435 nm in the 0.3 M [pmim][BF(4)] mixed micelle and from 25 to 100% in the 0.9 M [pmim][BF(4)] mixed micelle. It is suggested that, at λ(ex) = 435 nm, mainly the donor molecules present at the corona are excited, causing ultrafast FRET due to a short donor-acceptor distance. At shorter λ(ex), the donor (C480) molecule at the core regions is excited, giving rise to a very long 3400 ps component (R(DA) ∼ 50 Å). Thus, λ(ex) variation leads to excellent spatial resolution. The counterion dependence (Br(-) vs BF(4)(-)) is attributed to the difference in the local polarity and size of the two mixed micelles.
研究了含有室温离子液体 (RTIL) 的混合胶束中的超快荧光共振能量转移 (FRET)，采用皮秒和飞秒发射光谱法进行了研究。混合胶束由三嵌段共聚物（PEO）(20)-(PPO)（70)-(PEO)（20）（Pluronic P123）和 RTIL、1-戊基-3-甲基-咪唑四氟硼酸盐 ([pmim][BF(4)]) 或 1-戊基-3-甲基-咪唑溴化物 ([pmim][Br]) 组成。香豆素 480 (C480) 用作供体，而受体是罗丹明 6G (R6G)。检测到 FRET 的多个时间尺度-1-3 ps 的超快成分和两个相对较长的成分（300-400 ps 和 2500-3500 ps）。不同的时间尺度归因于不同的供体-受体距离。提出离子受体 (R6G) 定位于混合胶束的极性冠区，而中性供体 (C480) 分布在冠区和疏水区两者中。超快 (1-3 ps) 成分归因于供体和受体的紧密接触处的 FRET。对于在靠近受体的极性冠区中的供体，发生这种情况。较长的成分（300-400 ps 和 2500-3500 ps）是由于核心处的供体和冠区处的受体之间的远距离 FRET 产生的。FRET 的超快成分（约 3 ps）的相对贡献从 0.3 M [pmim][BF(4)] 混合胶束中在 λ(ex) = 375 nm 时的 5%增加到在 λ(ex) = 435 nm 时的 30%，并从 25%增加到 0.9 M [pmim][BF(4)] 混合胶束中的 100%。表明，在 λ(ex) = 435 nm 时，主要激发位于冠区的供体分子，由于供体-受体距离较短，导致超快 FRET。在较短的 λ(ex) 时，激发位于核区的供体 (C480) 分子，导致非常长的 3400 ps 成分（R(DA) ∼ 50 Å）。因此，λ(ex) 变化导致出色的空间分辨率。抗衡离子依赖性（Br(-) 与 BF(4)(-))归因于两种混合胶束的局部极性和尺寸的差异。
