Ghosh Subhadip, Dey Shantanu, Adhikari Aniruddha, Mandal Ujjwal, Bhattacharyya Kankan
Physical Chemistry Department, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, India.
J Phys Chem B. 2007 Jun 28;111(25):7085-91. doi: 10.1021/jp070235y. Epub 2007 May 27.
Fluorescence resonance energy transfer (FRET) from coumarin 480 (C480) to rhodamine 6G (R6G) is studied in the micelle and the gel phase of a triblock copolymer, (PEO)20-(PPO)70-(PEO)20 (Pluronic P123 (P123)) by picosecond and femtosecond emission spectroscopy. The time constants of FRET were obtained from the rise time of the acceptor (R6G) emission. In a P123 micelle, FRET occurs in multiple time scales: 2.5, 100, and 1700 ps. In the gel phase, three rise components are observed: 3, 150, and 2600 ps. According to a simple Förster model, the ultrafast (2.5 and 3 ps) components of FRET correspond to donor-acceptor distance RDA=13 +/- 2 A. The ultrafast FRET occurs between a donor and an acceptor residing at close contact at the corona (PEO) region of a P123 micelle. With increase in the excitation wavelength (lambdaex) from 375 to 435 nm, the relative contribution of the ultrafast component of FRET ( approximately 3 ps) increases from 13% to 100% in P123 micelle and from 1% to 100% in P123 gel. It is suggested that at lambdaex = 435 nm, mainly the highly polar peripheral region is probed where FRET is very fast due to close proximity of the donor and the acceptor. The 100 and 150 ps components correspond to RDA = 25 +/- 2 A and are ascribed to FRET from C480 deep inside the micelle to an acceptor (R6G) in the peripheral region. The very long component of FRET (1700 ps in micelle and 2600 ps component in gel) may arise from diffusion of the donor from outside the micelle to the interior followed by fast FRET.
通过皮秒和飞秒发射光谱，研究了三嵌段共聚物（PEO）20 -（PPO）70 -（PEO）20（普朗尼克P123（P123））的胶束和凝胶相中香豆素480（C480）到罗丹明6G（R6G）的荧光共振能量转移（FRET）。FRET的时间常数由受体（R6G）发射的上升时间获得。在P123胶束中，FRET发生在多个时间尺度上：2.5、100和1700皮秒。在凝胶相中，观察到三个上升成分：3、150和2600皮秒。根据一个简单的福斯特模型，FRET的超快（2.5和3皮秒）成分对应于供体 - 受体距离RDA = 13 ± 2埃。超快FRET发生在位于P123胶束冠部（PEO）区域紧密接触的供体和受体之间。随着激发波长（lambdaex）从375纳米增加到435纳米，FRET超快成分（约3皮秒）的相对贡献在P123胶束中从13%增加到100%，在P123凝胶中从1%增加到100%。据推测，在lambdaex = 435纳米时，主要探测的是高极性的外围区域，由于供体和受体靠得很近，FRET非常快。100和150皮秒成分对应于RDA = 25 ± 2埃，归因于从胶束内部深处的C480到外围区域受体（R6G）的FRET。FRET非常长的成分（胶束中为1700皮秒，凝胶中为2600皮秒成分）可能源于供体从胶束外部扩散到内部，随后发生快速FRET。
