In this review, the multifunctionality of dithieno[3,2-b:2',3'-d]thiophenes (DTTs) is covered comprehensively. This is of interest because all involved research is very recent, emphasizes timely topics such as mechanochemistry for bioimaging or chalcogen bonds for catalysis and solar cells, and because the newly emerging privileged scaffold is embedded in an inspiring structural space. At the beginning, DTTs are introduced with regard to nomenclature, constitutional isomers and optoelectronic properties. The structural space around DTTs is mapped out next with regard to heteroatom substitution in bridge and core, covering much of the periodic table, eccentric heteroatom doping and bridge expansions. After a brief summary of synthetic approaches to the DTT scaffold, chalcogen bonds are introduced as, together with redox switching and turn-on fluorescence, one of the three conceptual foundations of most multifunctionality. Realized functions cover anion binding, transport (ion carriers, ion channels), catalysis, and the first fluorescent probes to image physical forces in living cells.

Planarizable push-pull probes have been introduced to demonstrate physical forces in biology.However,the donors and acceptors needed to polarizem echanically planarized probes are incompatible with their twisted resting state.T he objective of this study was to overcome this "flipper dilemma" with chalcogen-bonding cascade switches that turn on donors and acceptors only in response to mechanical planarization of the probe.T his concept is explored by molecular dynamics simulations as well as chemical double-mutant cycle analysis. Cascade switched flipper probes turn out to excel with chemical stability,red shifts adding up to high significance,and focused mechanosensitivity.M ost important, however,i st he introduction of an ew,g eneral and fundamental concept that operates with non-trivial supramolecular chemistry,solves an important practical problem and opens aw ide chemical space.Planarizable push-pull (PP) chromophores have been introduced [1] as mechanosensitive [2] fluorescent membrane probes [1][2][3] to image membrane tension [4] in living cells. [5,6] The current best is constructed around twisted dithienothiophene (DTT) dithienothiophene S,S-dioxide (DTTO2) conjugates ( Figure 1a,D ' = S, A' = SO 2 ). [7] Thet wo "flippers" [7] are twisted out of coplanarity by repulsion between the methyls (light blue circles) and the s holes (dark blue ovals) [8][9][10][11] on the sulfurs next to the connecting bond ( Figure 1b,l eft, 1). The PP system is prepared first with "sulfide" donors and "sulfone" acceptors in the DTT and the DTTO2b ridges, respectively (Figure 1b, 8,9). 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). 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). 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). 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. Sulfides,p reviously introduced as covalent PP turn-on donors, [12] failed to afford operational probes. [14] Non-covalent 1,4-chalcogen bonds (1,4-CBs) [8][9][10][11] as in 1 were more successful, also because spontaneous degradation into reactive Figure 1. a) Flipper dilemma and b) CB cascade switch:a)Inplanarizable PP probes, exocyclic donors D D and acceptors A A are needed in planar but incompatiblew ith twisted form. b) Twisting of the central bond (1)turns off PP D D (2,r ed circle), and A A (3,b lue circle) because Lewis base Y( 5)hardly...

Bent N,N′‐diphenyl‐dihydrodibenzo[a,c]phenazine amphiphiles are introduced as mechanosensitive membrane probes that operate by an unprecedented mechanism, namely, unbending in the excited state as opposed to the previously reported untwisting in the ground and twisting in the excited state. Their dual emission from bent or “closed” and planarized or “open” excited states is shown to discriminate between micelles in water and monomers in solid‐ordered (So), liquid‐disordered (Ld) and bulk membranes. The dual‐emission spectra cover enough of the visible range to produce vesicles that emit white light with ratiometrically encoded information. Strategies to improve the bent mechanophores with expanded π systems and auxochromes are reported, and compatibility with imaging of membrane domains in giant unilamellar vesicles by two‐photon excitation fluorescence (TPEF) microscopy is demonstrated.

The combination of catalysis and transport across lipid bilayer membranes promises directional access to a solvent-free and structured nanospace that could accelerate, modulate, and, at best, enable new chemical reactions. To elaborate on these expectations, anion transport and catalysis with pnictogen and tetrel bonds are combined with polyether cascade cyclizations into bioinspired cation transporters. Characterized separately, synergistic anion and cation transporters of very high activity are identified. Combined for catalysis in membranes, cascade cyclizations are found to occur with a formal rate enhancement beyond one million compared to bulk solution and product formation is detected in situ as an increase in transport activity. With this operational system in place, intriguing perspectives open up to exploit all aspects of this unique nanospace for important chemical transformations.

Planarizable push-pull probes have been introduced to demonstrate physical forces in biology.However,the donors and acceptors needed to polarizem echanically planarized probes are incompatible with their twisted resting state.T he objective of this study was to overcome this "flipper dilemma" with chalcogen-bonding cascade switches that turn on donors and acceptors only in response to mechanical planarization of the probe.T his concept is explored by molecular dynamics simulations as well as chemical double-mutant cycle analysis. Cascade switched flipper probes turn out to excel with chemical stability,red shifts adding up to high significance,and focused mechanosensitivity.M ost important, however,i st he introduction of an ew,g eneral and fundamental concept that operates with non-trivial supramolecular chemistry,solves an important practical problem and opens aw ide chemical space.Planarizable push-pull (PP) chromophores have been introduced [1] as mechanosensitive [2] fluorescent membrane probes [1][2][3] to image membrane tension [4] in living cells. [5,6] The current best is constructed around twisted dithienothiophene (DTT) dithienothiophene S,S-dioxide (DTTO2) conjugates ( Figure 1a,D ' = S, A' = SO 2 ). [7] Thet wo "flippers" [7] are twisted out of coplanarity by repulsion between the methyls (light blue circles) and the s holes (dark blue ovals) [8][9][10][11] on the sulfurs next to the connecting bond (Figure 1b,l eft, 1). The PP system is prepared first with "sulfide" donors and "sulfone" acceptors in the DTT and the DTTO2b ridges, respectively (Figure 1b, 8,9). 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). 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). 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). 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. Sulfides,p reviously introduced as covalent PP turn-on donors, [12] failed to afford operational probes. [14] Non-covalent 1,4-chalcogen bonds (1,4-CBs) [8][9][10][11] as in 1 were more successful, also because spontaneous degradation into reactive Figure 1. a) Flipper dilemma and b) CB cascade switch:a)Inplanarizable PP probes, exocyclic donors D D and acceptors A A are needed in planar but incompatiblew ith twisted form. b) Twisting of the central bond (1)turns off PP D D (2,r ed circle), and A A (3,b lue circle) because Lewis base Y( 5)hardly ...

Bent N,N′‐diphenyl‐dihydrodibenzo[a,c]phenazine amphiphiles are introduced as mechanosensitive membrane probes that operate by an unprecedented mechanism, namely, unbending in the excited state as opposed to the previously reported untwisting in the ground and twisting in the excited state. Their dual emission from bent or “closed” and planarized or “open” excited states is shown to discriminate between micelles in water and monomers in solid‐ordered (So), liquid‐disordered (Ld) and bulk membranes. The dual‐emission spectra cover enough of the visible range to produce vesicles that emit white light with ratiometrically encoded information. Strategies to improve the bent mechanophores with expanded π systems and auxochromes are reported, and compatibility with imaging of membrane domains in giant unilamellar vesicles by two‐photon excitation fluorescence (TPEF) microscopy is demonstrated.

The acceptor strength of the 1,2-diphenyl-3,5-pyrazolidinedione residue is re-evaluated based on the spectral-fluorescent properties of donor–acceptor dyes. Low fluorescence of the title compounds is explained by the low-lying forbidden ππ*-state.

Design, synthesis and evaluation of push-pull N, N′-diphenyl-dihydrodibenzo[a,c]phenazines are reported. Consistent with theoretical predictions, donors and acceptors attached to the bent mechanophore are shown to shift absorption maxima to either red or blue, depending on their positioning in the chromophore. Redshifted excitation of push-pull fluorophores is reflected in redshifted emission of both bent and planar excited states. The intensity ratios of the dual emission in more and less polar solvents imply that excited-state (ES) planarization decelerates with increasing fluorophore macrodipole, presumably due to attraction between the wings of closed papillons. ES planarization of highly polarizable papillons is not observed in lipid bilayer membranes. All pushpull papillon amphiphiles excel with aggregation-induced emission (AIE) from bent ES as micelles in water and mechanosensitivity in viscous solvents. They are not solvatochromic and only weakly fluorescent (QY < 4%).2 .