Details

Autor(en) / Beteiligte

• Garci, Amine
• Beldjoudi, Yassine
• Kodaimati, Mohamad S
• Hornick, Jessica E
• Nguyen, Minh T
• Cetin, M. Mustafa
• Stern, Charlotte L
• Roy, Indranil
• Weiss, Emily A
• Stoddart, J. Fraser

Titel

Mechanical-Bond-Induced Exciplex Fluorescence in an Anthracene-Based Homo[2]catenane

Ist Teil von

• Journal of the American Chemical Society, 2020-04, Vol.142 (17), p.7956-7967

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2020

Quelle

MEDLINE

Beschreibungen/Notizen

• Collisional intermolecular interactions between excited states form short-lived dimers and complexes that lead to the emergence of excimer/exciplex emission of lower energy, a phenomenon which must be differentiated from the photoluminescence (PL) arising from the monomeric molecules. Although the utilization of noncovalent bonding interactions, leading to the generation of excimer/exciplex PL, has been investigated extensively, precise control of the aggregates and their persistence at very low concentrations remains a rare phenomenon. In the search for a fresh approach, we sought to obtain exciplex PL from permanent structures by incorporating anthracene moieties into pyridinium-containing mechanically interlocked molecules. Beyond the optical properties of the anthracene moieties, their π-extended nature enforces [π···π] stacking that can overcome the Coulombic repulsion between the pyridinium units, affording an efficient synthesis of an octacationic homo[2]­catenane. Notably, upon increasing the ionic strength by adding tetrabutyl­ammonium hexafluoro­phosphate, the catenane yield increases significantly as a result of the decrease in Coulombic repulsions between the pyridinium units. Although the ground-state photophysical properties of the free cyclophane and the catenane are similar and show a charge-transfer band at ∼455 nm, their PL characters are distinct, denoting different excited states. The cyclophane emits at ∼562 nm (quantum yield ϕF = 3.6%, emission lifetime τs = 3 ns in MeCN), which is characteristic of a disubstituted anthracene–pyridinium linker. By contrast, the catenane displays an exciplex PL at low concentration (10–8 M) with an emission band centered on 650 nm (ϕF = 0.5%, τs = 14 ns) in MeCN and at 675 nm in aqueous solution. Live-cell imaging performed in MIAPaCa-2 prostate cancer cells confirmed that the catenane exciplex emission can be detected at micromolar concentrations.