Institute of Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam, Germany.
J Phys Chem A. 2020 Dec 31;124(52):11017-11024. doi: 10.1021/acs.jpca.0c09911. Epub 2020 Dec 18.
9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and para-positions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para- and ortho-derivatives' charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range.
9,10-取代蒽类因其荧光等有用的光学性质而闻名，这使得它们经常被用作传感应用中的探针。在本文中，我们研究了三种吡啶取代变体的基本光物理性质。吡啶六元环中的氮原子与蒽核处于邻位、间位和对位。进行了吸收、荧光和瞬态吸收测量，并辅以理论计算。我们在氯仿和水中监测了蒽衍生物的光物理性质，研究了质子化形式及其非质子化形式。我们发现，非质子化形式的光学性质主要由蒽发色团决定，与其他 9,10-取代蒽类（例如二苯基蒽）只有很小的差异。相比之下，质子化会导致荧光强度和寿命显著降低。瞬态吸收测量和理论计算揭示了在质子化发色团中形成了电荷转移态，其中电子密度从蒽部分转移到质子化的吡啶取代基上。虽然对位和邻位衍生物的电荷转移仍然具有中等的荧光性，但间位衍生物受到的影响要强得多，几乎没有荧光。这种对质子化活性的氮原子位置依赖性敏感性使得这些荧光团的组合非常适合覆盖更宽 pH 范围的 pH 传感应用。
