Zero-Overlap Fluorophores for Fluorescent Studies at Any Concentration
Zero-Overlap Fluorophores for Fluorescent Studies at Any Concentration
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DOI：
10.1021/jacs.0c02450
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发表时间：
2020-07-15
影响因子：
15
通讯作者：
Flood, Amar H.
中科院分区：
文献类型：
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作者：
Dhara, Ayan;Sadhukhan, Tumpa;Flood, Amar H.
荧光团是研究化学、生物学和物理学的有力工具。然而，当浓度超过5 μ M时，由于发射光的自吸收和色移等效应，荧光受到严重损害。在此，我们报告了电荷转移（CT）荧光团的创建，并发现其在低浓度下的发射颜色即使在5 mM也不变，超过典型限制约3个数量级。该荧光团由三苯胺取代的蓝星大环组成，在633 nm处产生15 000 cm（-1）的显著斯托克斯位移。对该荧光团的性能至关重要的是观察到其发射光谱在325 nm处与吸收带接近零重叠。我们建议将光谱重叠减少到零是在所有浓度下实现全荧光的关键。大环的三苯胺供体和五个氰二苯乙烯受体单元产生发射CT态。与密切相关的供体-受体对照化合物显示双重发射不同，蓝星框架抑制第二态的发射，从而产生零重叠荧光团。我们展示了在毫摩尔浓度下使用发射光谱来表征主客体络合，这通常是核磁共振光谱的专有领域。pf6阴离子的结合产生2:1的夹心配合物，具有蓝移发射。与扭曲的分子内电荷转移（TICT）状态不同，实验支持的密度功能理论显示，在CT状态下，受体单元内部有67度的扭曲，而不是在供体和受体之间显示扭曲；它很像tict。受研究结果的启发，我们发现了一种对照化合物类似的浓度无关行为，强烈表明这种行为可能是潜在的其他大斯托克斯位移荧光团。我们讨论了能够产生零重叠荧光团的策略，以便在所有实际浓度下对过程进行准确的荧光表征。
Fluorophores are powerful tools for the study of chemistry, biology, and physics. However, fluorescence is severely impaired when concentrations climb above 5 mu M as a result of effects like self-absorption and chromatic shifts in the emitted light. Herein, we report the creation of a charge-transfer (CT) fluorophore and the discovery that its emission color seen at low concentrations is unchanged even at 5 mM, some 3 orders of magnitude beyond typical limits. The fluorophore is composed of a triphenylamine-substituted cyanostar macrocycle, and it exhibits a remarkable Stokes shift of 15 000 cm(-1) to generate emission at 633 nm. Crucial to the performance of this fluorophore is the observation that its emission spectrum shows near-zero overlap with the absorption band at 325 nm. We propose that reducing the spectral overlap to zero is a key to achieving full fluorescence across all concentrations. The triphenylamine donor and five cyanostilbene acceptor units of the macrocycle generate an emissive CT state. Unlike closely related donor-acceptor control compounds showing dual emission, the cyanostar framework inhibited emission from the second state to create a zero-overlap fluorophore. We demonstrated the use of emission spectroscopy for characterization of host-guest complexation at millimolar concentrations, which are typically the exclusive domain of NMR spectroscopy. The binding of the PF6-anion generates a 2:1 sandwich complex with blue-shifted emission. Distinct from twisted intramolecular charge-transfer (TICT) states, experiment-supported density functional theory shows a 67 degrees twist inside an acceptor unit in the CT state instead of displaying a twist between the donor and acceptor; it is TICT-like. Inspired by the findings, we uncovered similar concentration-independent behavior from a control compound, strongly suggesting this behavior may be latent to other large Stokes-shift fluorophores. We discuss strategies capable of generating zero-overlap fluorophores to enable accurate fluorescence characterization of processes across all practical concentrations.