Design and synthesis of molecular turnstiles.

Abstract

Macrobicycles 1-3 have been prepared by palladium-catalyzed double macrocyclization. The planar geometry of this system is such that the para axis of the inner ring exactly matches the inner diameter of the macrocycle. Molecular models suggest that the inner ring of 1 should be able to rotate freely about its long axis, acting like the spindle of a turnstile. For large spindle substituents, this rotation will become hindered while for intermediate sized substituents, a pair of energetically equivalent conformational states should rapidly interconvert on an experimentally observable time scale. Substituted derivatives 2 and 3 possess diastereotopic methylene protons which become operationally enantiotopic upon fast rotation. Based on variable-temperature 'H NMR and longitudinal T\ relaxation experiments, examples of what are believed to be freely rotating 2 and conformationally locked 3 spindles are reported. These molecules represent the first iteration in the development of phenylacetylene macrocycles possessing conformational bistability that may eventually lead to new types of solids or liquid crystals that respond rapidly to external electric fields.Recently, several examples that may be considered mechanical molecular devices have been reported including Stoddart's rotaxane based molecular shuttle,2 Feringa's chiroptical molecular switch,3 Jprgenson's light activated bianthrone molecules,4 Kelly's molecular "brake",5 6*and Malthete and Collet's conformationally invertable columnar mesophases.6,7 Despite these and other impressive examples, two formidable obstacles toward the continued development of molecular-based devices present themselves to modem chemistry. These include the development of general schemes for the predictable assembly of multimolecular aggregates in all

Probing the structure of a rotaxane with two-dimensional infrared spectroscopy

“…I t has recently become possible to synthesize molecules that function like mechanical devices (1)(2)(3)(4), such as switches (5-7), motors (8)(9)(10)(11), brakes (12), turnstiles (13), and elevators (14). These manmade molecular machines can be considered as nanoscale versions of their macroscopic analogues.…”

Molecular dynamics of a grid-mounted molecular dipolar rotor in a rotating electric field

“…Molecular rotors driven unidirectionally by light (8), or bidirectionally by heat (9)(10)(11)(12) or chemically (13,14) have been synthesized. Alternating electric field has been used to affect intramolecular motion (15), and intense laser field of rapidly rotating linear polarization has been used to drive the rotation of a chlorine molecule (16).…”

Molecular machines operated by light

“…In the last few years the development of powerful synthetic methodologies, combined with a device-driven ingenuity evolved from the attention to functions and reactivity, have led to remarkable achievements in this field. Among the systems reported are molecular tweezers [9], propellers [10], rotors [11], turnstiles [12], gyroscopes [13,14], gears [15], brakes [16], a molecular pedal [17], ratchets [18], rotary motors [19], shuttles [20], elevators [21], muscles [22], valves [23], processive artificial enzymes [24], walkers [25][26][27], vehicles [28], and catalytic self-propelled micro-and nano-objects [29,30]. Several excellent reviews [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] and a monograph [47] dealing with artificial molecular machines and motors are available.…”