Turn-On Sulfide π Donors: An Ultrafast Push for Twisted Mechanophores

Abstract

Attached to electron-rich aromatic systems, sulfides are very weak acceptors; however, attached to electron-poor aromatics, they turn into quite strong donors. Here, we show that this underappreciated dual nature of sulfides deserves full consideration for the design of functional systems. Tested with newly designed and synthesized planarizable push-pull mechanophores, sulfide acceptors in the twisted ground state are shown to prevent oxidative degradation and promote blue-shifting deplanarization. Turned on in the planar excited state, sulfide donors promote red-shifting polarization. Impressive Stokes shifts are the result. Demonstrating the usefulness of time-resolved broadband emission spectra to address significant questions, direct experimental evidence for the ultrafast (3.5 ps), polarity-independent and viscosity-dependent planarization from the twisted Franck-Condon S1 state to the relaxed S1 state could be secured.

A Chalcogen‐Bonding Cascade Switch for Planarizable Push–Pull Probes

“…Such behavior is opposite to molecular rotors, [2] but consistent with the viscosity dependence of the excited state untwisting into the emissive planar form. [12] Thef luorescence decrease was accompanied by only as mall (< 10 nm) red shift of the excitation maximum (Figure 4e). These results support that the large red shifts and the fluorescence enhancements observed with the probes 1-4 in ordered phase of membranes originate from planarization and polarization in the ground state,reporting on the spacial confinement in equilibrium.…”

“…The PP system is prepared first with "sulfide" donors and "sulfone" acceptors in the DTT and the DTTO2b ridges, respectively (Figure 1b, 8,9). [12] To achieve significant red shifts upon planarization in the ground state,a dditional PP donors Da nd acceptors Aa re required (Figure 1a). Thee mission maximum is nearly mechanoinsensitive because the probes emit only from the planar form.…”

“…[12] To achieve significant red shifts upon planarization in the ground state,a dditional PP donors Da nd acceptors Aa re required (Figure 1a). Sulfides,p reviously introduced as covalent PP turn-on donors, [12] failed to afford operational probes. Because both DTTs and DTTO2are comparably electron-rich, [13] this problem is more pronounced on the DTT side.T herefore,Dand As hould ideally turn on only in response to flipper planarization.…”

“…Conjugation of DTT and DTTO2u pon mechanical co-planarization then turns on this intrinsic PP system and shifts the excitation maximum to the red (Figure 1b,r ight). [12] To achieve significant red shifts upon planarization in the ground state,a dditional PP donors Da nd acceptors Aa re required (Figure 1a). [12] To achieve significant red shifts upon planarization in the ground state,a dditional PP donors Da nd acceptors Aa re required (Figure 1a).…”

“…These exocyclics ubstituents represent atrue dilemma because in the twisted resting state,the DTT donors and DTTO2 acceptors,a tl east partially decoupled from each other and equipped with extra Da nd A, could become too rich and too poor in electron density,respectively, and decompose easily (Figure 1a). Sulfides,p reviously introduced as covalent PP turn-on donors, [12] failed to afford operational probes. Sulfides,p reviously introduced as covalent PP turn-on donors, [12] failed to afford operational probes.…”