Mencaroni Letizia, Bianconi Tommaso, Aurora Mancuso Maria, Sheokand Manju, Elisei Fausto, Misra Rajneesh, Carlotti Benedetta
Department of Chemistry, Biology and Biotechnology and CEMIN, University of Perugia, 06123, Perugia, Italy.
Department of Chemistry, University of Wisconsin-Madison, 53706, Madison, USA.
Chemistry. 2025 Jan 17;31(4):e202403388. doi: 10.1002/chem.202403388. Epub 2024 Nov 25.
The pH effect on the photophysics of three push-pull compounds bearing dimethoxytriphenylamine (TPA-OMe) as electron donor and pyridine as electron acceptor, with different ortho-functionalization (-H, -Br, and -TPA-OMe), is assessed through steady-state and time-resolved spectroscopic techniques in DMSO/water mixed solutions and in water dispersions over a wide pH range. The enhanced intramolecular charge transfer upon protonation of the pyridinic ring leads to the acidochromic (from colorless to yellow) and acido(fluoro)chromic (from cyan to pink) behaviours of the investigated compounds. In dilute DMSO/buffer mixtures these molecules exhibited low pK values (≤3.5) and extremely short singlet lifetimes. Nevertheless, it is by exploiting the aggregation phenomenon in aqueous environment that the practical use of these compounds largely expands: i) the basicity increases (pKa≈4.5) approaching the optimum values for pH-sensing in cancer cell recognition; ii) the fluorescence efficiencies are boosted due to Aggregation-Induced Emission (AIE), making these compounds appealing as fluorescent probes; iii) longer singlet lifetimes enable Excited-State Proton Transfer, paving the way for the application of these molecules as photobases (pK*=9.1). The synergy of charge and proton transfers combined to the AIE behaviour in these pyridines allows tunable multi-responsive optical properties providing valuable information for the design of new light-emitting photobases.
通过稳态和时间分辨光谱技术，在宽pH范围内的二甲基亚砜/水混合溶液和水分散体中，评估了pH对三种推拉型化合物光物理性质的影响。这三种化合物以二甲氧基三苯胺（TPA-OMe）作为电子供体，吡啶作为电子受体，具有不同的邻位官能团（-H、-Br和-TPA-OMe）。吡啶环质子化后分子内电荷转移增强，导致所研究化合物呈现酸致变色（从无色到黄色）和酸（氟）致变色（从青色到粉红色）行为。在稀二甲基亚砜/缓冲液混合物中，这些分子表现出低pK值（≤3.5）和极短的单线态寿命。然而，正是通过利用水环境中的聚集现象，这些化合物的实际应用得到了很大扩展：i）碱性增加（pKa≈4.5），接近癌细胞识别中pH传感的最佳值；ii）由于聚集诱导发光（AIE），荧光效率提高，使这些化合物作为荧光探针具有吸引力；iii）更长的单线态寿命能够实现激发态质子转移，为这些分子作为光碱（pK*=9.1）的应用铺平了道路。这些吡啶中电荷转移和质子转移与AIE行为的协同作用，使得可调谐的多响应光学性质成为可能，为新型发光光碱的设计提供了有价值的信息。
