A new class of crystalline X-ray induced photochromic materials assembled from anion-directed folding of a flexible cation

Electron-deficient viologens are widely used as ligands or structure-directing agents(SDAs)to synthesize crystalline X-ray induced photochromic materials.Here,a new rational strategy of anion-directed fold-ing a flexible cation(H_(2)imb)^(2+)((H_(2)imb)^(2+)=di-protonated 2,3-bis(imidazolin-2-yl)-2,3-dimethylbutane)has been developed.Electron-donating Cl−and(ZnCl4)2−are used to direct folding a flexible electron-deficient(H_(2)imb)^(2+)cation.Three complexes(H_(2)imb)(NO_(3))2(1),(H_(2)imb)Cl2·H_(2)O(2),and(H_(2)imb)ZnCl4(3)have been synthesized in which(H_(2)imb)^(2+)crystallize in an anti-conformation,88.8°-gauche,and 51.8°-gauche,respectively.In contrary to X-ray silent complex 1,X-ray induced photochromism has been achieved in both complex 2 and 3.An intermolecular charge-transfer mechanism has been elucidated and the anion directed folding of(H_(2)imb)^(2+)has been validated to be critical to yield colored long-lived charge-separated states.

Langmuir−Blodgett Nanoarchitectonics,Out of the Box

KITCHEN CHEMISTRY TO FOREFRONT MOLECULAR SCIENCE The Langmuir−Blodgett(LB)method is an old technique with a more than 100-year history.Its principle is simply based on spreading of a thin film(mostly monolayer)of waterless soluble molecules on water,which is similar to daily life common events such as oil dropping on water.It is said that the initial research on the relation between surface tension(as parameter related with surface pressure)and monolayer compression was pioneered by a self-taught German women scientist Agnes Pockels using a handmade trough in her family kitchen.1 After systematic research efforts on monolayers at the air−water interface by Irving Langmuir,2 formation of multilayer films through simple transfer of monolaters from a water surface to a solid surface was demonstrated with the aid of Katherine Blodgett to initiate the Langmuir−Blodgett(LB)technique.3 Although sophisticated film balances have been developed and a huge variety of components has been subjected to the LB method,the fundamental principles with simple procedures remain unchanged over 100 years.

Using orbital sensitivity analysis to pinpoint the role of orbital interactions in thermoelectric power factor

The modification of the electronic band structure is of critical importance for thermoelectric materials whose heat to electricity power generation is related to carrier effective mass and alignment of semiconductor band edges.One approach to optimize the electronic band structure is by modification of orbital interactions through doping or alloying.While the current ab-initio quantum chemical calculations can help us to investigate orbital components of electronic bands,they reveal little information on the relative tunability of electronic states and transport properties with respect to orbital interactions.In this work,we present a method,based on a symmetry-adapted tight-binding model and sensitivity analysis,that can pinpoint the role of orbital interactions in determining electronic band structure and transport properties.As an application,a systematic theoretical analysis is used to show how the power factor of PbTe can/cannot be improved by playing with interatomic orbital interactions.The orbital interaction sensitivity analysis introduced in this work can easily be applied to other compounds or properties.