The variation with the intermolecular distance of features in hydrogen bond (HB) dimers dependent on the electron density ρ(r) are studied in four complexes representative of weak/medium HB interactions. Topological properties, energy densities and integrated atomic properties are obtained with ρ(r) of dimers at B3LYP/6-311++G(d,p) optimized structures obtained upon fully relaxing the geometry of monomers. The dependence of A–H⋯B bond properties on intermolecular R(H⋯B) distances allows to characterize the nature of the interaction as monomers move nearer from infinite separation. At long distances the interaction is only electrostatic while for separations about 1 Å larger than the equilibrium distance Req, quantum effects arising from ρ(r) begin to dominate. In the immediate neighborhood of Req the interaction is mainly led by the stabilization of the H-donor due in turn to energy lowerings in A and B atoms associated to polarization effects. The mutual penetration of electron densities of donor and acceptor monomers provokes a considerable reduction of atomic volumes for H and B atoms which reveals in the form of redistribution rather than transfer of charge. This range of distances exhibits noncovalent bond features but shortly after, when monomers approximate a few tenths of Å below Req, characteristics typical of covalent interactions begin to appear while the rate of change of all the ρ(r)-dependent properties increases rapidly.

The variation with the intermolecular distance of geometries, energies, and other properties dependent on the electron density ρ(r) are studied in three cyclic dimers linked by two hydrogen bonds: formic acid and formamide homodimers and the heterodimer formamide/formic acid complex. Topological features, energy densities and integrated atomic properties provided by AIM theory are calculated with ρ(r) obtained at B3LYP/6-311++G(d,p) optimized geometries for a number of intermonomer distances covering large separations, equilibrium, and short distances. The variation with these distances of properties studied allows to characterize the nature of the interaction in A–H⋯B (A=N, O and B=O) hydrogen bonds. Whereas at large distances the attraction is purely electrostatic, quantum effects associated with redistributions of ρ(r) mainly around H and B atoms dominate the interaction in the neighborhood of equilibrium. Mutual penetration of the electron densities of these atoms leads to considerable reductions of their atomic volumes and associated polarization effects as well as energetic stabilization of atom A. Although the interaction in this range of intermonomer separations displays noncovalent features, when the dimers move at distances shorter than equilibrium, characteristics typical of covalent interactions begin to appear while the systems leave the planar structures presented until then. This work complements our previous study [O. Galvez, P. C. Gomez, and L. F. Pacios, J. Chem. Phys. 115, 11166 (2001)] of dimers with one single hydrogen bond.

The splitting of some rotational lines due to a predicted hydrogen atom migration in protonated acetylene, [Formula: see text], was not observed in the first pure rotational spectroscopy experiment in the vibrational ground state. An improvement of the spectral resolution of the spectrometer has allowed the observation of some of these small splittings. They have been interpreted within the semi-rigid bender model. Numerical results are presented for different values of the barrier height. Reasonable agreement between observed and calculated splittings is obtained with a barrier of about 1600 cm−1, which is 15% higher than the most recent ab initio value.

Hybrid organic–inorganic perovskite solar cells have recently emerged as one of the most promising low‐cost photovoltaic technologies. The remarkable progress of perovskite photovoltaics is closely related to advances in interfacial engineering and development of charge selective interlayers. Herein, we present the synthesis and characterization of a fused azapolyheteroaromatic small molecule, namely anthradi‐7‐azaindole (ADAI), with outstanding performance as a hole‐transporting layer in perovskite solar cells with inverted architecture. Its molecular arrangement, induced by hydrogen‐bond‐directed self‐assembly, favors a suitable morphology of the perovskite layer, reducing the effects of recombination as revealed by light intensity dependence, photoluminescence, and electroluminescence studies.

Lead-tin (Pb-Sn) hybrid perovskite materials possess ideal narrow bandgaps (1.2-1.4 eV) for efficient single-junction and tandem solar cells. Poly (3,4ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is commonly used as hole transport layer (HTL) for Pb-Sn perovskite solar cells (PSCs), despite its poor stability with these perovskites. Here, two new octacyclic heteroaromatic molecules, pyrenodiindole (PDI) and pyrenodi-(7-azaindole) (PDAI), are presented as the HTL for narrow-bandgap (1.23 eV) p-i-n Pb-Sn PSCs. The selfassembled reciprocal hydrogen-bonded solid-state structure of PDAI bestows robustness compared to PDI, making it less vulnerable in processing the perovskite film on top, and improves the reproducibility of device fabrication. Transient photocurrent measurements and light-intensity-dependent device characteristics indicate that PDI and PDAI possess similar hole extraction properties to PEDOT:PSS. As a result, similar open-circuit voltages and fill factors are obtained in the PSCs. Interestingly, the use of thin PDI and PDAI as HTL in PSCs changes the optical interference and reduces parasitic absorption in the near-infrared region, resulting in an improved short-circuit current density. Consequently, a higher power conversion efficiency of 16.1% is obtained for PDI and PDAI, compared to 15.1% for PEDOT:PSS. In addition, the self-assembled structure of PDAI led to a notable enhancement of device stability.