# High-Pressure Structural and Electronic Properties of Bibenzyl (1,2-Diphenylethane) from Synchrotron SC-XRD and Two-Photon-Induced Fluorescence

## TL;DR

This study explores how pressure affects the structure and electronic properties of bibenzyl, revealing a phase transition that impacts its potential for creating carbon nanothreads.

## Contribution

The novel contribution is the discovery of a pressure-induced phase transition in bibenzyl linked to π–π interactions and structural distortions.

## Key findings

- A phase transition occurs at 13 GPa, tripling the a axis and asymmetric unit.
- Two-photon-induced fluorescence shows π–π interactions stabilize the electronic ground state at the phase transition.
- Molecular distortions at the transition make bibenzyl less reactive to pressure-induced polymerization.

## Abstract

The structural and electronic properties of bibenzyl
(1,2-diphenylethane)
are investigated as a function of pressure using single-crystal X-ray
diffraction (SC-XRD) and two-photon-induced fluorescence. Bibenzyl
is an appealing pseudostilbene compound for the high-pressure synthesis
of mixed carbon nanothreads with tunable optical properties, due to
its fully saturated linking group. Crystal structures are refined
from ambient pressure up to 37 GPa by synchrotron XRD, and the appearance
of pseudosymmetry traits at 13 GPa reveals a phase transition that
consists of molecular distortions leading to the tripling of the a axis and asymmetric unit while maintaining the unit cell's
point group symmetry. Two-photon-induced fluorescence up to 18 GPa
provides insights into the structural changes where the strengthening
of π–π interactions at the phase transition stabilizes
the electronic ground state and drives the molecular distortions that
occur at that pressure. Coupling structural and electronic properties
rationalizes the high-pressure reactivity compared to other pseudostilbenes,
showing that the molecular evolution from the added torsional degree
of freedom and establishment of π–π interactions
at the phase transition lead the molecular conformation to an unfavorable
state for pressure-induced polymerization.