Is a Single Conformer Sufficient to Describe the Reorganization Energy of Amorphous Organic Transport Materials?

The reorganization energy (λ), which quantifies the structural rearrangement of a molecule when accommodating a charge, is a key parameter in the evaluation of charge mobility in molecular solids. However, it is unclear how λ is influenced by conformational isomerism, which co-exist in amorphous solids. Here, we examine the conformational space of a family of model amorphous organic hole transport materials (HTMs), derived from triphenylamine in a core-arm template, and probe the effect of conformational complexity on λ. We observe an extreme dependence of λ on the conformer geometry of sterically congested HTMs, which to the best of our knowledge has not been described previously. These results serve as a cautionary tale that, while extracting the reorganization energy from a single molecular conformer optimized in the gas phase may be appropriate for rigid and sterically unencumbered structures, it is not for many state-of-the-art HTMs that contain multiple bulky substituents.<br>

Is a Single Conformer Sufficient to Describe the Reorganization Energy of Amorphous Organic Transport Materials?

The reorganization energy (λ), which quantifies the structural rearrangement of a molecule when accommodating a charge, is a key parameter in the evaluation of charge mobility in molecular solids. However, it is unclear how λ is influenced by conformational isomerism, which co-exist in amorphous solids. Here, we examine the conformational space of a family of model amorphous organic hole transport materials (HTMs), derived from triphenylamine in a core-arm template, and probe the effect of conformational complexity on λ. We observe an extreme dependence of λ on the conformer geometry of sterically congested HTMs, which to the best of our knowledge has not been described previously. These results serve as a cautionary tale that, while extracting the reorganization energy from a single molecular conformer optimized in the gas phase may be appropriate for rigid and sterically unencumbered structures, it is not for many state-of-the-art HTMs that contain multiple bulky substituents.<br>

Previtamin D: Z–E photoisomerization via a Hula-twist conical intersection

Ring opening of 7-dehydrocholesterol in a cold matrix yields a single conformer of previtamin D, a steroid Z-triene. On its photoisomerization, the main product results from Hula twist (HT), and side products (e.g. from double-bond twist, DBT) come from the same conical intersection.

Polymorphs of the antiviral drug ganciclovir

Ganciclovir (GCV; systematic name: 2-amino-9-{[(1,3-dihydroxypropan-2-yl)oxy]methyl}-6,9-dihydro-1H-purin-6-one), C9H13N5O4, an antiviral drug for treating cytomegalovirus infections, has two known polymorphs (Forms I and II), but only the structure of the metastable Form II has been reported [Kawamura & Hirayama (2009). X-ray Struct. Anal. Online, 25, 51–52]. We describe a successful preparation of GCV Form I and its crystal structure. GCV is an achiral molecule in the sense that its individual conformers, which are generally chiral objects, undergo fast interconversion in the liquid state and cannot be isolated. In the crystalline state, GCV exists as two inversion-related conformers in Form I and as a single chiral conformer in Form II. This situation is similar to that observed for glycine, also an achiral molecule, whose α-polymorph contains two inversion-related conformers, while the γ-polymorph contains a single conformer that is chiral. The hydrogen bonds are exclusively intermolecular in Form I, but both inter- and intramolecular in Form II, which accounts for the different molecular conformations in the two polymorphs.

Conformational variety of flexible mono-dentate ligands in coordination compounds: influence of π-involving interactions

Inspection of the packing of synthesized compounds clearly shows that π-involving intermolecular interactions including πnaph⋯πnaph and πimine⋯πpy/naph with the cooperation of Hg⋯πpy can lock the ligand conformational variety to a single conformer.

Structure, vibrational spectroscopy, and photochemistry of 5-phenoxy-1-phenyltetrazole in argon and nitrogen cryomatrices

The molecular structure, infrared spectra, and photochemistry of 5-phenoxy-1-phenyltetrazole (5PPT) isolated in argon and N2 cryogenic matrices were investigated by infrared spectroscopy and theoretical calculations (DFT(B3LYP)/6-311++G(d,p)). Calculations yield two dissimilar minima on the potential energy surface of the molecule, both being eightfold degenerate by symmetry and belonging to the C1 symmetry point group. Extensive analysis of the potential energy landscape of the molecule was performed. Upon consideration of the zero-point vibrational correction to the energy, the calculations predict that the higher energy minimum shall relax barrierlessly to the lower energy form, leading to conclude that the compound exists in a single conformer in the gas phase. Accordingly, a single conformer was observed and fully characterized spectroscopically upon isolation of the monomer of the compound in argon and nitrogen cryomatrices. UV-laser irradiation (λ = 250 nm) of matrix-isolated 5PPT leads to photocleavage of the tetrazole ring, with release of N2 and formation of the corresponding carbodiimide.