Photoswitchable Quadruple Hydrogen-Bonding Motif.

Multiple hydrogen-bonding motifs serve as important building blocks for molecular recognition and self-assembly. Herein, a photoswitchable quadruple hydrogen-bonding motif featuring near-complete, reversible, and thermostable conversion between DADA and AADD arrays associated with an alteration of their dimerization constants by over 3 orders of magnitude is reported. The system is based on a diarylethene featuring a ureidopyrimidin-4-ol moiety, which upon photoinduced ring closure and associated loss of aromaticity undergoes enol-keto tautomerization to a ureidopyrimidinone moiety. The latter causes a transformation of the hydrogen-bonding arrays and significantly weakens the free energy of dimerization in the case of the closed isomer. This photoswitchable quadruple hydrogen-bonding motif should allow us to spatially and temporarily direct self-assembly and supramolecular polymerization processes by light.

Embedded Localized Molecular-Orbital Representations for Periodic Wave Functions.

To more straightforwardly provide local chemical-bonding reasoning in crystalline matter, we introduce a new approach to generate a real-space analogue of periodic electronic structures using "exact" top-down frozen-density embedding calculations. Based on the obtained real-space electronic structure, we then construct localized molecular orbitals and evidence that our technique compares favorably against the commonly used Wannier method, both in terms of numerical efficiency and details of chemical bonding. The new method has been implemented into the LOBSTER software package and designed as a black-box approach, digesting any periodic electronic structure from the currently supported codes, i.e., VASP, Quantum ESPRESSO, and ABINIT.