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The goal of this combined experimental and computational study is to investigate the structural conformation of oligo( para -phenylenes) in the crystalline phase, in particular the planarity of this type of molecules. To this end we have performed Raman experiments on para -terphenyl and para -quaterphenyl in a pressure range from 0 to 70 kbar and at temperatures from 10 to 300 K. The positions and the relative intensities of the C–C interring stretch mode at 1280 cm −1 and the C–H in-plane bend mode at 1220 cm −1 have been tracked. We find that upon increasing temperature at ambient pressure the intensity ratio I 1280 / I 1220 drops rapidly at temperatures that coincide with the crystallographic phase transition for the investigated materials. At ambient temperature also, this intensity ratio drops rapidly upon increasing pressure up to about 15 kbar. In the computational part, the Raman frequencies and activities of isolated 3P and 4P molecules were calculated within restricted Hartree–Fock formalism with the interring tilt angles varying from 0 to 90°. These calculations confirm that the I 1280 / I 1220 intensity ratio can be related to the planarity of the molecules. Three-dimensional bandstructure calculations within density functional theory were applied to determine phonon frequencies and estimate Raman activities for the polymer poly( para -phenylene). These simulations show that the same conclusions hold for crystalline environment.

Molecular interfaces formed between metals and molecular compounds offer a great potential as building blocks for future opto-electronics and spintronics devices. Here, a combined theoretical and experimental spectro-microscopy approach is used to show that the charge transfer occurring at the interface between nickel tetraphenyl porphyrins and copper changes both spin and oxidation states of the Ni ion from [Ni(II), S = 0] to [Ni(I), S = 1/2]. The chemically active Ni(I), even in a buried multilayer system, can be functionalized with nitrogen dioxide, allowing a selective tuning of the electronic properties of the Ni center that is switched to a [Ni(II), S = 1] state. While Ni acts as a reversible spin switch, it is found that the electronic structure of the macrocycle backbone, where the frontier orbitals are mainly localized, remains unaffected. These findings pave the way for using the present porphyrin-based system as a platform for the realization of multifunctional devices where the magnetism and the optical/transport properties can be controlled simultaneously by independent stimuli., Small;17(50)