October 21, 2013: Isomorphic polymorphs found! – While polymorphism is the ability of a given structure to crystallize in different forms, isomorphism is the ability of two or more distinct structures to adopt the same crystal packing. As described in our recent paper in Crystal Growth and Design, the systematic replacement of hydrogen by fluorine atoms in the phenylene rotator of a series of steroidal molecular rotors leads to the formation of several sets of isomorphic polymorphs. Some of their structures are related by loss of solvent and/or by thermal phase transitions.
July 18, 2013: Rotation in crystals is determined by the size and symmetry of the rotator - Smaller rotators have smaller moments of inertia and fewer van der Waas contacts to hinder their motion, which makes them faster. It is therefore remarkable that a relatively large bicyclo[2.2.2]octane, with an activation energy of only Ea = 1.15 kcal mol−1, has faster rotational motion than smaller methyl and methoxy groups in the same steroidal structure. In our most recent JACS article, we describe how to sort out the dynamics of the three different groups and we explain how the misalignment between crystallographic and BCO symmetry axes creates an advantageous 6-fold axial symmetry order that more than makes up for its larger size.
April 10, 2013: Large differences in size and shape between the triazoline reactants and aziridine products provide the means to document solid-to-solid reactions that follow different phase transformation mechanisms. Denisse de Loera’s JACS article documents the quantitative thermal and photochemical formation of aziridines with bulky substituents.
October 29, 2012: Just published in The Journal of Organic Chemistry as a Feature Article, work carried out with the groups of Profs. J. Morzycki in Poland and R. Santillan in Mexico describes an efficient seven-step synthetic route and the internal dynamics of two beautiful crystalline macrocyclic molecular rotors.
July 19, 2012: Aziridines crystals are “born” in a metastable form - The photodenitrogenation of crystalline triazolines generates the corresponding aziridines in nearly quantitative yields. Using powder X ray diffraction to monitor the photoreaction progress, it was shown that the packing structure of the starting material remains in the product obtained. The study is detailed in Denisse de Loera’s just published Organic Letters paper.
February 16, 2012: 2D Glasses!!! - Molecular rotors confined in two dimensions form rotational glasses and rotational liquids. Cortnie Vogelsberg's recent Journal of Physical Chemistry B article describes this phenomenon with p-divinylphenylene rotators in a hierarchically ordered periodic mesoporous organosilica. The study reveals non-Arrhenius dynamics and an increase in heat capacity characteristic of a phase transition. This unprecedented discovery is an exceptional platform for the development of hypersensitive thermally activated molecular machines. Congrats, Cortnie!
October 24, 2011: Cortnie Vogelsberg’s Chem. Soc. Rev. article “Crystalline molecular machines: function, phase order, dimensionality, and composition” is now available as an Advance Article here! This thought provoking critical review is a great introduction to the developing field of amphidynamic molecular machines and their potential. It is also a great read to catch up on the latest progress in the field. Congrats, Cortnie!
September 23, 2011: How to cross three bridges in one step - A very nice synthetic strategy was devised to construct molecular gyroscopes with three bridges (shown in green) in only one step. Their single crystal X-ray structures reveal that the molecular gyroscopes pack in ordered sheets, which will be ideal for structures with interacting polar rotators. Read Patrick Commins’ and Jose Nunez’s synthetic strategy in the Journal of Organic Chemistry.
September 22, 2011: The Case of the Short-Lived Triplets - Using transient spectroscopy to determine the excited lifetimes of nanocrystalline benzophenones, we determined why certain triplet states are extremely short lived in solids but not in solution. The triplet excited states of the substituted benzophenones are quenched by an adjacent molecule in the ground state via a reductive charge transfer (CT) mechanism. Hot off of the press, see the “just accepted” JACS full article describing Greg Kuzmanich and Matt Gard’s work in collaboration with the group of Prof. Guldi.
May 23, 2011: Challenging Reactions Gone Green - Crystals of hexasubstituted ketones exposed to light, without solvents or any other reagents, give quantitative yields of products with all-carbon adjacent quaternary stereogenic centers, which are very difficult to obtain otherwise. Crystalline ketones were easily generated by trapping tertiary carbanions with a carbonyl source and the subsequent solid-state reaction gave the product with complete diastereoselectivity. The method developed by Saori Shiraki just appeared in Photochemical and Photobiological Sciences.
May 20, 2011: Life in the Fast Lane - Using ultrafast pulses
the excited kinetics of a nanocrystalline indanone, we discovered that the
reaction in crystals can be very fast; starting with a singlet biradical,
visting the triplet state, and then going on to the product in less than
10 nanoseconds. See the Chemical Science edge article describing
Greg Kuzmanich's work in collaboration with Profs. Tito Scaiano,
JosÚ-Carlos Netto-Ferrerria, and Matt Platz.
May 18, 2011: First 1D rotor chain! - Collaborative studies bridged by Braulio Rodriguez-Molina between our group at UCLA and the Santillan group in CINVESTAV, Mexico, led to the discovery of the first crystalline array of molecular rotors that undergo correlated motions in a 1D chain. Read this work in: J. Am. Chem. Soc., 2011, 133, 7280.
April 21, 2011: Towards Exploded Stators - Zach
and solid state NMR study of a new molecular gyroscope with "exploded"
tri-(meta-terphenyl)methyl stators shows that steric bulk and rigidity
yields robust yet low-density crystals capable of accommodating phenylene
rotation in excess of 100 MHz at room temperature.
April 11, 2011: Add halogen-bonding to the toolbox of crystal engineering
techniques for amphidynamic molecular machines. Cortnie
Vogelsberg's solid-state NMR analysis of crystalline
1,4-bis(iodoethynyl)bicyclo[2.2.2]octane showed that halogen-bonded
molecular rotors sustain ultra-fast rotation. This study, in
collaboration with Prof. Stuart Brown and the group of Prof.
Patrick Batail, validates an unprecedented approach to the
construction of amphidynamic molecular machines where the extended
framework itself provides the template to sustain engineered rotation to
very low temperatures. See the ASAP JACS article here!
February 8, 2011: Oxyallyl is Blue! Even though oxyallyl is
reaction intermediate involved in many organic reactions, until now, it
had resisted all attempts at direct detection, isolation, and
characterization. See here the JACS communication describing Greg Kuzmanich's work
collaboration with the groups of Profs. Dirk M. Guldi and Kendall Houk.