Linear, Non-Conjugated Cyclic and Conjugated Cyclic Paraphenylene under Pressure

Abstract

The n-paraphenylene family comprises chains of phenylene units linked together by C-C bonds that are between single- and double-bonded, and where n corresponds to the number of phenylene units. In this work, we compare the response of the optical properties of different phenylene arrangements. We study linear chains (LPP), cyclic systems (CPPs), and non-conjugated cyclic systems with two hydrogenated phenylenes (H4[n]CPP). Particularly, the systems of interest in this work are [6]LPP, [12]- and [6]CPP and H4[6]CPP. This work combines Raman and infrared spectroscopies with absorption and fluorescence (one- and two-photon excitations) measured as a function of pressure up to maximum of about 25 GPa. Unprecedented crystallographic pressure-dependent results are shown on H4[n]CPP, revealing intramolecular π-π interactions upon compression. These intramolecular interactions justify the H4[n]CPP singular optical properties with increasing fluorescence lifetime as a function of pressure.

Second Order Phase Transition and Stabilizing CH···H and CH···S Interactions in Naphthyl End-Capped Bithiophene at 3.5 GPa

“…Second, we describe interaction directionalities and identify new sulfur–hydrogen contacts that demonstrate the fundamental difference between thiophenes and acenes and other fused-ring molecules. This complements earlier ambient as well as high-pressure studies of thiophenes, small π-conjugated molecules, polymers, and other materials. − …”

A Chichibabin’s Hydrocarbon-Based Molecular Cage: The Impact of Structural Rigidity on Dynamics, Stability, and Electronic Properties

“…It is well-known that π-conjugated molecules undergo a wide range of conformational transformations under high pressure, which can also be used to modulate the electro-optical properties of materials. Therefore, it would be of great interest to investigate conformational and electronic diversity of a conjugated cage-shaped molecule consisting of both quinoidal and aromatic phenyl rings.…”

“…Considering the unique π–π stacking as observed in the crystal of c -Ph14 6+ , it is reasonable to assume that pressure is transmitted intermolecularly through direct contacts between the benzene-1,3,5-triyl bridgeheads (Figure b). In parallel, the biphenyl quinoidal cores are subsequently deformed to reduce the molar volume . Notice that the nature of the pressure effect in these two bands is different as revealed by the different behavior of their wavenumbers with pressure (see Figure S20 in SI).…”

“…Detailed studies on the neutral molecules as well as their charged species allow us to understand how the structural rigidity in a 3D π-conjugated molecular cage affects the molecular dynamics, stability, and electronic properties. In addition, the rigid cage-like structure also offers the possibility to investigate free volume cavity controlled properties such as pressure-dependent quinoid-benzenoid interconversion, and host–guest chemistry with fullerenes …”