Untitled

Abstract

A molecular-level abacus-like system driven by light inputs has been designed in the form of a [2]rotaxane, comprising the pi-electron-donating macrocyclic polyether bis-p-phenylene-34-crown-10 (BPP34C10) and a dumbbell-shaped component that contains 1) a Ru(II) polypyridine complex as one of its stoppers in the form of a photoactive unit, 2) a p-terphenyl-type ring system as a rigid spacer, 3) a 4,4'-bipyridinium unit and a 3,3'-dimethyl-4,4'-bipyridinium unit as pi-electron-accepting stations, and 4) a tetraarylmethane group as the second stopper. The synthesis of the [2]rotaxane was accomplished in four successive stages. First of all, the dumbbell-shaped component of the [2]rotaxane was constructed by using conventional synthetic methodology to make 1) the so-called "west-side" comprised of the Ru(II) polypyridine complex linked by a bismethylene spacer to the p-terphenyl-type ring system terminated by a benzylic bromomethyl function and 2) the so-called "east-side" comprised of the tetraarylmethane group, attached by a polyether linkage to the bipyridinium unit, itself joined in turn by a trismethylene spacer to an incipient 3,3'-dimethyl-4,4'-bipyridinium unit. Next, 3) the "west-side" and "east-side" were fused together by means of an alkylation to give the dumbbell-shaped compound, which was 4) finally subjected to a thermodynamically driven slippage reaction, with BPP34C10 as the ring, to afford the [2]rotaxane. The structure of this interlocked molecular compound was characterized by mass spectrometry and NMR spectroscopy, which also established, along with cyclic voltammetry, the co-conformational behavior of the molecular shuttle. The stable translational isomer is the one in which the BPP34C10 component encircles the 4,4'-bipyridinium unit, in keeping with the fact that this station is a better pi-electron acceptor than the other station. This observation raises the question- can the BPP34C10 macrocycle be made to shuttle between the two stations by a sequence of photoinduced electron transfer processes? In order to find an answer to this question, the electrochemical, photophysical, and photochemical (under continuous and pulsed excitation) properties of the [2]rotaxane, its dumbbell-shaped component, and some model compounds containing electro- and photoactive units have been investigated. In an attempt to obtain the photoinduced abacus-like movement of the BPP34C10 macrocycle between the two stations, two strategies have been employed-one was based fully on processes that involved only the rotaxane components (intramolecular mechanism), while the other one required the help of external reactants (sacrificial mechanism). Both mechanisms imply a sequence of four steps (destabilization of the stable translational isomer, macrocyclic ring displacement, electronic reset, and nuclear reset) that have to compete with energy-wasteful steps. The results have demonstrated that photochemically driven switching can be performed successfully by the sacrificial mechanism, whereas, in the case of the intramolecu...

Autonomous artificial nanomotor powered by sunlight

“…Electrochemical and NMR spectroscopic data showed (29) that the stable conformation of 1 6ϩ is by far the one in which the R component is located around the better electron acceptor station, A 1…”

“…In a previous work (29), we reported on the rotaxane 1 6ϩ (Scheme 1) that was carefully designed and synthesized to perform as a linear molecular motor powered exclusively by visible light, with autonomous operation relying on intramolecular processes. In such a work, however, we only succeeded in demonstrating the operation of the rotaxane as a light-driven mechanical switch that needed alternate addition of two ''fuels,'' namely triethanolamine and oxygen, with concomitant generation of waste products.…”

Implementation of simple logic gates on gold–ammonia bonding patterns in different charge states

“…[5][6][7][8][9][10] In parallel, several groups have shown that it is possible realize complex combinational logic circuits at the molecular scale, up to half and full addition or subtraction using various external perturbations, i.e., chemical, biochemical, photochemical, optical, electrochemical, electrical, to address the system, encode the inputs and perform the logic operations. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] We propose here another approach for implementing molecular logic gates.…”

Artificial Photochemical Devices and Machines

“…On the basis of the experience gained with pseudorotaxane model systems [62], the rotaxane 19 6þ (Figure 1.17) was specifically designed [63] to achieve photoinduced ring shuttling in solution. This compound has a modular structure; its ring component R is a p-electron-donating bis-p-phenylene [34]crown-10, whereas its dumbbell component is made of several covalently linked units.…”

“…The molecular shuttle 19 6þ can also be operated, with a higher quantum yield, by a sacrificial mechanism [63] based on the participation of external reducing (triethanolamine) and oxidizing (dioxygen) species and by an intermolecular mechanism [64] involving the kinetic assistance of an external electron relay (phenothiazine), which is not consumed. However, operation by the sacrificial mechanism does not afford an autonomous behavior and leads to consumption of chemical fuels and formation of waste products.…”