Architecturally diverse nanostructured foldamers reveal insightful photoinduced single-molecule dynamics
Architecturally diverse nanostructured foldamers reveal insightful photoinduced single-molecule dynamics
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DOI：
10.1021/ja078302p
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发表时间：
2008-06-04
影响因子：
15
通讯作者：
Li, Alexander D. Q.
中科院分区：
文献类型：
--
作者：
Han, Jason J.;Shaller, Andrew D.;Li, Alexander D. Q.
单分子荧光光谱已用于探测结构多样且独特的模型低聚物，其中恰好包含两个或四个二萘嵌苯四羧酸二酰亚胺（PTDI）单元：线性折叠体lin 2和lin 4、单环互补物cyc 2和级联可折叠环cat 4。线性，循环和级联的折叠体揭示了光吸收和激发诱导展开和重折叠，产生从一种光谱类型到另一种光谱类型的彩色光谱切换。折叠分子结构决定了展开和重折叠过程，因此也决定了光谱动力学。因此，线性四聚体表现出积极的帧到帧的光谱切换伴随着显着的颜色变化，但级联的四聚体显示一个多色的复合光谱，很少或没有光谱切换。激发态动力学导致光谱切换：电子解耦的PTDI单体发射绿色荧光，而电子耦合的PTDI T-堆叠发射红色荧光，较长的π-堆叠发射更红的荧光。我们解决的一个关键问题是激发态离域长度，或激子相干长度，在T-栈，这已被证明是难以直接测量。使用具有受控序列、结构和明确定义的长度和发色团数目的折叠体，我们绘制出了π堆叠中的激子相干长度。对发色折叠体的单分子荧光研究表明，最大结构域长度在四个g-堆叠的PTDI染料之间是离域的，并且对于超出四聚体的低聚物没有发现新的纯色。因此，π堆叠中的荧光颜色的范围是发色团的数量的函数，仅直到四聚体。
Single molecule fluorescence spectroscopy has been used to probe architecturally diverse and unique model oligomers containing exactly two or four perylene tetracarboxylic diimide (PTDI) units: linear foldamers lin2 and lin4, monocyclic complement cyc2, and concatenated foldable rings cat4. Linear, cyclic, and concatenated foldamers reveal that photoabsorption and excitation induces unfolding and refolding, generating colorful spectral switching from one spectral type to another. Foldamer architectures dictate the unfolding and refolding processes, and hence the spectral dynamics. As a result, linear tetramer exhibits active frame-to-frame spectral switching accompanying dramatic changes in colors, but a concatenated tetramer displays a multicolored composite spectrum with little or no spectral switching. Excited state dynamics causes spectral switching: an electronically decoupled PTDI monomer emits green fluorescence while electronically coupled PTDI T-stacks emit red fluorescence, with longer pi-stacks emitting redder fluorescence. A key question we address is the excited-state delocalization length, or the exciton coherence length, in the T-stacks, which has been proven difficult to measure directly. Using foldamers having controlled sequences, structures, and well-defined length and chromophore numbers, we have mapped out the exciton coherence length in pi-stacks. Single molecule fluorescence studies on chromophoric foldamers reveal that the maximum domain length is delocalized across just four g-stacked PTDI dyes and no new pure color can be found for oligomers beyond the tetramer. Therefore, the range of fluorescent colors in pi-stacks is a function of the number of chromophores only up to the tetramer.