Analytical Applications of Excited-state proton transfer (ESPT) in Pyrene-Based Photoacids

质子转移反应作为最基本的反应之一，已被广泛研究了60多年。我们最近发表了一系列基于著名的光酸吡喃(8-羟基吡喃-1，3，6-三磺酸)的光酸，它们在激发态的pKa值低至-4。然而，除了用于研究反应动力学外，这些光酸还可以预见更多的应用。质子按需，即通过可见的超短激光脉冲激发，可以触发类似酮-烯醇重排的反应级联反应，然后可以例如通过时间分辨红外光谱进行研究。当分子停留在激发态几纳秒时，观察到双发射。由于光酸在质子转移前的激发态寿命只有皮秒，因此可以用高灵敏度的Förster共振能量转移在较低的纳米范围内进行距离测量。当更多的(光)化学活性侧基连接到芘核上时，可以产生更多的发射态。预期的应用仍然是过去未能实现的想法，因为所有三个磺酸盐侧基同时被转化为更强的吸电子部分。为了克服目前的局限性，我们提出了两种方法：一方面，用氮杂芘代替芘作为起始原料，从而得到更强的光酸。这些衍生品将会对两个合作伙伴产生极大的兴趣。另一方面，我们引入了辅助取代，并通过X-射线结晶学进行了验证，这使得我们能够有区域选择性地修饰芘核心。赠款提案的精髓是致力于这些化合物的合成，我们预计这些化合物将保持我们以前羟基芘衍生物的有益性质，即高荧光量子产率、高光稳定性和电磁光谱可见范围内的电子跃迁。

Proton-transfer as one of the most fundamental reactions is intensively studied for more than 60 years. We recently published a series of photoacids on the basis of the well-known photoacid pyranine (8-Hydroxypyrene-1,3,6-trisulfonate) which exhibit pKA-values in the excited-state down to -4. However, more applications of these photoacids can be foreseen beyond their use for studying reaction dynamics. Protons-on-demand, i.e. by excitation with visible ultrashort laser-pulses, can trigger reaction cascades like keto-enol rearrangements which can then be studied e.g. by time-resolved IR spectroscopy. As the molecules stay in the excited-state for several nanoseconds, dual emission is observed. The lifetime in the excited-state of the photoacid before the proton-transfer, only lasting for picoseconds, allows for distance measurement in the lower nanometer range by Förster-resonance energy transfer with ultrasensitivity. More emissive states can be created when more (photo)chemically active side groups are attached to the pyrene core.The anticipated applications are yet ideas which withstood realization in the past as all three sulfonate side groups were simultaneously transformed to stronger electron-withdrawing moieties. We propose two approaches to overcome the current limitations: on the one hand, pyrene as starting material will be replaced by aza-pyrene from which even stronger photoacids are figured out. These derivatives would be of great interest for two collaboration partners. On the other hand, we introduced helper substitution, verified by x-ray crystallography, which enables us to modify the pyrene core regioselectively. The marrow of the grant proposal is dedicated to the synthesis of these compounds from which we expect maintenance of the beneficial properties of our previous hydroxy-pyrene derivatives, i.e. high fluorescence quantum yields, high photostabilities and electronic transitions in the visible range of the electromagnetic spectrum.