Ionic manipulation of charge-transfer and photodynamics of [60]fullerene confined in pyrrolo-tetrathiafulvalene cage.

A cage molecule incorporating three electron donating monopyrrolotetrathiafulvalene units was synthesised to host electron accepting [60]fullerenes. Formation of a strong 1 : 1 donor-acceptor (D-A) complex C60⊂1 was confirmed by solid state X-ray analysis as well as 1H NMR and absorption spectroscopic analyses of the arising charge-transfer (CT) band (λ = 735 nm, ε ≈ 840 M-1 cm-1). Inserting Li+ inside the [60]fullerene increased the binding 28-fold (Ka = 3.7 × 106 M-1) and a large bathochromic shift of the CT band to the near infrared (NIR) region (λ = 1104 nm, ε ≈ 4800 M-1 cm-1) was observed.

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes.

The electron-donor and unique redox properties of the tetrathiafulvalene (TTF, 1) moiety have led to diverse applications in many areas of chemistry. Monopyrrolotetrathiafulvalenes (MPTTFs, 4) and bispyrrolotetrathiafulvalenes (BPTTFs, 5) are useful structural motifs and have found widespread use in fields such as supramolecular chemistry and molecular electronics. Protocols enabling the synthesis of functionalised MPTTFs and BPTTFs are therefore of broad interest. Herein, we present the synthesis of a range of functionalised MPTTF and BPTTF species. Firstly, the large-scale preparation of the precursor species N-tosyl-(1,3)-dithiolo[4,5-c]pyrrole-2-one (6) is described, as well as the synthesis of the analogue N-tosyl-4,6-dimethyl-(1,3)-dithiolo[4,5-c]pyrrole-2-one (7). Thereafter, we show how 6 and 7 can be used to prepare BPTTFs using homocoupling reactions and functionalised MPTTFs using cross-coupling reactions with a variety of 1,3-dithiole-2-thiones (19). Subsequently, the incorporation of more complex functionality is discussed. We show how the 2-cyanoethyl protecting group can be used to afford MPTTFs functionalised with thioethers, exemplified by a series of ethylene glycol derivatives. Additionally, the merits of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an alternative to the most common deprotecting agent, CsOH·H2O are discussed. Finally, we show how a copper-mediated Ullman-type reaction can be applied to the N-arylation of MPTTFs and BPTTFs using a variety of aryl halides.

Robust inclusion complexes of crown ether fused tetrathiafulvalenes with Li⁺@C60 to afford efficient photodriven charge separation.

Inclusion complexes of benzo- and dithiabenzo-crown ether functionalized monopyrrolotetrathiafulvalene (MPTTF) molecules were formed with Li(+)@C60(1⋅Li(+)@C60 and 2⋅Li(+)@C60). The strong complexation has been quantified by high binding constants that exceed 10(6) M(-1) obtained by UV/Vis titrations in benzonitrile (PhCN) at room temperature. On the basis of DFT studies at the B3LYP/6-311G(d,p) level, the orbital interactions between the crown ether moieties and the π surface of the fullerene together with the endohedral Li(+) have a crucial role in robust complex formation. Interestingly, complexation of Li(+)@C60 with crown ethers accelerates the intersystem crossing upon photoexcitation of the complex, thereby yielding (3)(Li(+)@C60)*, when no charge separation by means of (1)Li(+)@C60* occurs. Photoinduced charge separation by means of (3)Li(+)@C60* with lifetimes of 135 and 120 µs for 1⋅Li(+)@C60 and 2⋅Li(+)@C60, respectively, and quantum yields of 0.82 in PhCN have been observed by utilizing time-resolved transient absorption spectroscopy and then confirmed by electron paramagnetic resonance measurements at 4 K. The difference in crown ether structures affects the binding constant and the rates of photoinduced electron-transfer events in the corresponding complex.

Ion-regulated allosteric binding of fullerenes (C60 and C70) by tetrathiafulvalene-calix[4]pyrroles.

The effect of ionic species on the binding of fullerenes (C60 and C70) by tetrathiafulvalene-calix[4]pyrrole (TTF-C4P) receptors and the nature of the resulting supramolecular complexes (TTF-C4P + fullerene + halide anion + tetraalkylammonium cation) was studied in the solid state through single crystal X-ray diffraction methods and in dichloromethane solution by means of continuous variation plots and UV-vis spectroscopic titrations. These analyses revealed a 1:1 stoichiometry between the anion-bound TTF-C4Ps and the complexed fullerenes. The latter guests are bound within the bowl-like cup of the C4P in a ball-and-socket binding mode. The interactions between the TTF-C4P receptors and the fullerene guests are highly influenced by both the nature of halide anions and their counter tetraalkylammonium cations. Three halides (F(-), Cl(-), and Br(-)) were studied. All three potentiate the binding of the two test fullerenes by inducing a conformational change from the 1,3-alternate to the cone conformer of the TTF-C4Ps, thus acting as positive heterotropic allosteric effectors. For a particular halide anion, the choice of tetraalkylammonium salts serves to modulate the strength of the TTF-C4P-fullerene host-guest binding interactions and, in conjunction with variations in the halide anion, can be exploited to alter the inherent selectivity of the host for a given fullerene. Differences in binding are reflected in the excited state optical properties. Overall, the present four-component system provides an illustration of how host-guest binding events involving appropriately designed artificial receptors can be fine-tuned via the addition of simple ionic species as allosteric modulators.

Chromo-fluorogenic detection of nitroaromatic explosives by using silica mesoporous supports gated with tetrathiafulvalene derivatives.

Three new hybrid gated mesoporous materials (SN3 -1, SNH2 -2, and SN3 -3) loaded with the dye [Ru(bipy)3 ](2+) (bipy=bipyridine) and capped with different tetrathiafulvalene (TTF) derivatives (having different sizes and shapes and incorporating different numbers of sulfur atoms) have been prepared. The materials SN3 -1 and SN3 -3 are functionalized on their external surfaces with the TTF derivatives 1 and 3, respectively, which were attached by employing the "click" chemistry reaction, whereas SNH2 -2 incorporates the TTF derivative 2, which was anchored to the solid through an amidation reaction. The final gated materials have been characterized by standard techniques. Suspensions of these solids in acetonitrile showed "zero release", most likely because of the formation of dense TTF networks around the pore outlets. The release of the entrapped [Ru(bipy)3 ](2+) dye from SN3 -1, SNH2 -2, and SN3 -3 was studied in the presence of selected explosives (Tetryl, TNT, TNB, DNT, RDX, PETN, PA, and TATP). SNH2 -2 showed a fairly selective response to Tetryl, whereas for SN3 -1 and SN3 -3 dye release was found to occur with Tetryl, TNT, and TNB. The uncapping process in the three materials can be ascribed to the formation of charge-transfer complexes between the electron-donating TTF units and the electron-accepting nitroaromatic explosives. Finally, solids SNH2 -2 and SN3 -1 have been tested for Tetryl detection in soil with good results, pointing toward a possible use of these or similar hybrid capped materials as probes for the selective chromo-fluorogenic detection of nitroaromatic explosives.

Selective redox-active molecular receptors for K+ and Ag+.

Two new tetrathiafulvalene based receptors in which the favorable redox properties of the tetrathiafulvalene unit are coupled to either a benzo-crown (X = O) or a dithiabenzo-crown (X = S) ether binding site were designed and synthesized as receptors for K(+) and Ag(+). The receptors display a good (K(+), X = O) to strong (Ag(+), X = S) affinity toward the cation and a high discrimination against other metal cations.