Figure 11. (a) Schematic illustration of a crank mechanism that translates linear motion into rotary motion in cylinder engines. (b) Schematic representation of a molecular crank mechanism. (c) Chemical structure of a synthetic molecular crank 5. 201 Reprinted with permission from ref 201.

The field of molecular logic gates originated 25 years ago, when A. P. de Silva published a seminal article in Nature. Stimulated by this ground breaking research, scientists were inspired to join the race to simulate the workings of the fundamental components of integrated circuits using molecules. The rules of this game of mimicry were flexible, and have evolved and morphed over the years. This tutorial review takes a look back on and provides an overview of the birth and growth of the field of molecular logics. Spinning-off from chemosensor research, molecular logic gates quickly proved themselves to be more than intellectual exercises and are now poised for many potential practical applications. The ultimate goal of this vein of research became clearer only recently - to "boldly go where no silicon-based logic gate has gone before" and seek out a new deeper understanding of life inside tissues and cells.

Acid fuels the motion of a threaded ring A central goal in the construction of molecular-scale machines is the efficient achievement of one-way motion. Erbas-Cakmak et al. developed a class of machines that transmit pH changes into the two-stage guided motion of molecular rings threaded on a linear or cyclic axle. The design relies on temporary blocking groups and landing sites along the axle that toggle between active and passive states in response to acid or base. Trichloroacetic acid initiates the first stage of motion until it is decomposed by base in the solution, spurring the second phase. Science , this issue p. 340

Guided by the digital design concepts, we synthesized a two-module molecular demultiplexer (DEMUX) where the output is switched between emission at near IR, and cytotoxic singlet oxygen, with light at 625 nm as the input (I), and acid as the control (c). In the neutral form, the compound fluoresces brightly under excitation at 625 nm, however, acid addition moves the absorption bands of the two modules in opposite directions, resulting in an effective reversal of excitation energy transfer direction, with a concomitant upsurge of singlet oxygen generation and decrease in emission intensity.

Cataloged from PDF version of article.A polymer-embedded dendritic, bodipy-based panchromatic absorber with a built-in energy gradient concentrates incident solar radiation at a terminal chromophore, resulting in a monochromatized emission directed to the sides of the polymer waveguide (see picture). This particular design minimizes self-absorption losses from the peripheral antenna units with an impressive S factor of 10 000