Equilibrium and thermodynamic studies of chromic overcrowded fluorenylidene-acridanes with modified fluorene moieties

Ya Wang,Yutaka Matsuo,Bing Wang,Keisuke Ogumi,Yue Ma,Yao Fu,Takafumi Nakagawa

doi:10.1038/s42004-020-00345-6

Abstract

Chromic materials, an important class of stimuli-responsive materials, have aroused extensive attention in recent years. Normally, their color is based on changes in morphology. Few examples of chromic material based on conformational isomerization, such as in overcrowded alkenes, have been reported previously. Furthemore, experimental thermodynamic studies of overcrowded bistricyclic aromatic enes have not been carried out to our knowledge. Here, we show that N-phenyl-substituted fluorenylidene-acridanes, with a properly modified fluorene moiety, performs chromisms originating from conformational changes. Thermodynamic studies determine equilibrium constants, changes in enthalpy, entropy, and free energy in solution, enabling in-depth understanding of the equilibrium behavior of overcrowded alkenes and providing useful information for designing functional chromic compounds. Single-crystal X-ray diffraction analysis of fluorenylidene-acridanes in this work clearly shows well-tuned charge transfer from the acridane to the fluorene moiety. Various chromic behaviors such as mechanochromism, thermochromism, solvatochromism, vapochromism, and proton-induced chromism also support understanding of conformational isomerism.

Highlights

Chromic materials, an important class of stimuli-responsive materials, have aroused extensive attention in recent years
The history of overcrowded bistricyclic aromatic enes (BAEs, Fig. 1) can be traced back almost one-hundred years, when they were used to discover the phenomenon of thermochromism[1]
In this work, we discuss equilibrium constants in terms of ratios of two conformers at different temperatures to investigate changes in enthalpy, entropy, and Gibbs free energy arising from this conformational isomerism

Summary

Introduction

An important class of stimuli-responsive materials, have aroused extensive attention in recent years Their color is based on changes in morphology. Thermodynamic studies determine equilibrium constants, changes in enthalpy, entropy, and free energy in solution, enabling in-depth understanding of the equilibrium behavior of overcrowded alkenes and providing useful information for designing functional chromic compounds. Single-crystal X-ray diffraction analysis of fluorenylidene-acridanes in this work clearly shows well-tuned charge transfer from the acridane to the fluorene moiety Various chromic behaviors such as mechanochromism, thermochromism, solvatochromism, vapochromism, and proton-induced chromism support understanding of conformational isomerism. To meet the requirements for practical applications, the chromic materials should revert back to their initial state from the perturbed state In this regard, chromic materials with conformational change are believed to have better functionality in the control of various efficient and reversible chromic processes. In this work, we discuss equilibrium constants in terms of ratios of two conformers at different temperatures to investigate changes in enthalpy, entropy, and Gibbs free energy arising from this conformational isomerism

Methods

Results

Conclusion