多足化合物的分子内激基缔合物形成及pH对其荧光的影响

THE INTRAMOLECULAR EXCIMER FORMATION AND THE pH EFFECT ON THE FLUORESCENCE OF MULTI-PEDAL COMPOUNDS

研究了含萘脲基多足化合物溶液的稳态和瞬态光物理行为 .由于分子内不同足间脲基的相互作用干扰了萘基的π π叠合 ,使分子内萘基的激基缔合物生成受到影响 .实验表明 :由于三足化合物存在着给电子叔胺基团 ,因此当萘基被激发时、可因分子内的光诱导电子转移而导致荧光猝灭 .正因如此 ,在三足化合物归一化后的稳态光谱中激基缔合物的发光强度很弱 .用皮秒级单光子记数技术测得该化合物的瞬态荧光为三指数衰变过程 .其中最长寿命的物种 ,即属于生成激基缔合物后再分解为萘激发态的部分仅占总量的 4 % ,与稳态的结果相一致 .工作表明对这类可用作荧光化学敏感器的三足化合物 ,如利用其激基缔合物的强度变化为其识别外来物种的敏感部位并不适合 .相反 ,如引入的外来物种能影响化合物的分子内光诱导电子转移 ,进而影响萘基的发光强度 。

The steady and transient state photo physical behaviors of multi pedal naphthyl urea derivatives were studied in this work. It is due to the fact that the interaction between urea groups perturbs the π π overlap of naphthyl groups resulting in a negative effect on the excimer formation of naphthalene. Experiments show that because the electronic donating group, tertiary amine, exists in the molecule 1, the fluorescence of excited naphthyl group can be quenched via the intra molecular electron transfer process. In this case, although the fluorescence of excimer can be observed by method of spectrum normalization from the steady state spectra of tri podal compound, but the intensity is quite weak. In addition, the pico second single photon counting method is used to measure the fluorescence life time of these compounds. It is found that the decay process of transient species is an tri exponential one. The emission species with the longest life time is attributed to the formation and decomposition of naphthalene excimer. The quantity of the largest life time component in total excited species is just only 4%. This corresponds to the results obtained from the steady state study. The results indicate that for the compound 1, used as a fluorescence chemical sensor, the change of fluorescence of the excimer used as a sensing part for the detection of foreign species is not suitable. On the contrary, if the foreign species introduced is able to affect the degree of intra molecular electron transfer of this compound, and furthermore to affect the fluorescence intensity of naphthalene, it should be a very sensitive way to indicate whether the complexation of guest molecule with host occurs.