美国化学会志(JACS)2013-09-05 2:57 AM

Crystalline Arrays of Pairs of Molecular Rotors: Correlated Motion, Rotational Barriers, and Space-Inversion Symmetry Breaking Due to Conformational Mutations - Journal of the American Chemical Society (ACS Publications)

The rod-like molecule bis((4-(4-pyridyl)ethynyl)bicyclo[2.2.2]oct-1-yl)buta-1,3-diyne, 1, contains two 1,4-bis(ethynyl)bicyclo[2.2.2]octane (BCO) chiral rotators linked by a diyne fragment and self-assembles in a one-dimensional, monoclinic C2/c centrosymmetric structure where two equilibrium positions with large occupancy imbalance (88% versus 12%) are identified on a single rotor site. Combining variable-temperature (70–300 K) proton spin–lattice relaxation, 1H T1–1, at two different 1H Larmor frequencies (55 and 210 MHz) and DFT calculations of rotational barriers, we were able to assign two types of Brownian rotators with different activation energies, 1.85 and 6.1 kcal mol–1, to the two 1H spin–lattice relaxation processes on the single rotor site. On the basis of DFT calculations, the low-energy process has been assigned to adjacent rotors in a well-correlated synchronous motion, whereas the high-energy process is the manifestation of an abrupt change in their kinematics once two blades of adjacent rotors are seen to rub together. Although crystals of 1 should be second harmonic inactive, a large second-order optical response is recorded when the electric field oscillates in a direction parallel to the unique rotor axle director. We conclude that conformational mutations by torsional interconversion of the three blades of the BCO units break space-inversion symmetry in sequences of mutamers in dynamic equilibrium in the crystal in domains at a mesoscopic scale comparable with the wavelength of light used. A control experiment was performed with a crystalline film of a similar tetrayne molecule, 1,4-bis(3-((trimethylsilyl)ethynyl)bicyclo[1.1.1]pent-1-yl)buta-1,3-diyne, whose bicyclopentane units can rotate but are achiral and produce no second-order optical response.

KEYWORDS

SHARE & LIKE

COMMENTS

ABOUT THE AUTHOR

美国化学会志(JACS)

0 Following 2 Fans 0 Projects 101 Articles

SIMILAR ARTICLES

The rod-like molecule bis((4-(4-pyridyl)ethynyl)bicyclo[2.2.2]oct-1-yl)buta-1,3-diyne, 1, contains two 1,4-bis(ethynyl)bicyclo[2.2.2]octane (BCO) chira

Read More

The rod-like molecule bis((4-(4-pyridyl)ethynyl)bicyclo[2.2.2]oct-1-yl)buta-1,3-diyne, 1, contains two 1,4-bis(ethynyl)bicyclo[2.2.2]octane (BCO) chira

Read More

Proteins exist in a delicate balance between the native and unfolded states, where thermodynamic stability may be sacrificed to attain the flexibility

Read More

Proteins exist in a delicate balance between the native and unfolded states, where thermodynamic stability may be sacrificed to attain the flexibility

Read More

We examine important reactivity pathways relevant to stoichiometric and catalytic C–H amination via isolable β-diketiminato dicopper alkylnitrene inter

Read More

We examine important reactivity pathways relevant to stoichiometric and catalytic C–H amination via isolable β-diketiminato dicopper alkylnitrene inter

Read More

Nucleic acid aptamers are receptors of single-stranded oligonucleotides that specifically bind to their targets. Significant interest is currently focu

Read More

Nucleic acid aptamers are receptors of single-stranded oligonucleotides that specifically bind to their targets. Significant interest is currently focu

Read More

The synthesis of the Lewis acid–base adducts of B(C6F5)3 and BF3 with [DAAmRe(O)(X)] DAAm = N,N-bis(2-arylaminoethyl)methylamine; aryl = C6F5 (X = Me,

Read More

The synthesis of the Lewis acid–base adducts of B(C6F5)3 and BF3 with [DAAmRe(O)(X)] DAAm = N,N-bis(2-arylaminoethyl)methylamine; aryl = C6F5 (X = Me,

Read More