Chapter 4
Mechano-Responsive Luminescence
via Crystal-to-Crystal Phase Transitions
Between Chiral and Non-chiral Space
Groups
A novel mechano-responsive luminescent (MRL) material based on crystal-to-crystal
phase transitions between crystals of a chiral and those of a centrosymmetric space
group, accompanied by a change of emission properties, is described. Initially, a
gold complex containing a biphenyl moiety, which exhibits an achiral structure
in solution, afforded an orange-emitting amorphous phase together with a viscous
isotropic oil after evaporation of the solvent. Upon pricking, the orange-emitting oil
spontaneously crystallized either in a centrosymmetric or in a chiral space group
while simultaneously changing the emission properties. Remarkably, grinding the
chiral crystals induced a solid-state phase transition to the achiral crystals under
concomitant changes of the emission properties.
4.1 Introduction
Research on mechano-responsive luminescent (MRL) materials has rapidly grown
over the past decade due to the strong interest in the underlying fundamental mechanisms, and on account of the potential applications [1]. In many cases, the changes
to the chemical bonding or structure on the molecular level, which are caused by
a macroscopic mechanical stimulus, are responsible for the alternation of the properties of such MRL compounds [1, 2]. Several basic design concepts for mechanoresponsive luminescent materials have been proposed [1]. For example, Moore and
co-workers have developed mechano-responsive polymers by introducing segments
called mechanophores, whose chemical structures are very sensitive to the force that
is applied [1a]. Introducing flexible substituents in a rigid luminescent core represents another design strategy to achieve MRL properties, which has been reported by
Sagara and Kato for liquid crystalline materials [1c]. Focusing on crystalline MRL
© Springer Nature Singapore Pte Ltd. 2020
M. Jin, Novel Luminescent Crystalline Materials of Gold(I) Complexes
with Stimuli-Responsive Properties, Springer Theses,
https://doi.org/10.1007/978-981-15-4063-9_4
103
Mechano-Responsive Luminescence
via Crystal-to-Crystal Phase Transitions
Between Chiral and Non-chiral Space
Groups
A novel mechano-responsive luminescent (MRL) material based on crystal-to-crystal
phase transitions between crystals of a chiral and those of a centrosymmetric space
group, accompanied by a change of emission properties, is described. Initially, a
gold complex containing a biphenyl moiety, which exhibits an achiral structure
in solution, afforded an orange-emitting amorphous phase together with a viscous
isotropic oil after evaporation of the solvent. Upon pricking, the orange-emitting oil
spontaneously crystallized either in a centrosymmetric or in a chiral space group
while simultaneously changing the emission properties. Remarkably, grinding the
chiral crystals induced a solid-state phase transition to the achiral crystals under
concomitant changes of the emission properties.
4.1 Introduction
Research on mechano-responsive luminescent (MRL) materials has rapidly grown
over the past decade due to the strong interest in the underlying fundamental mechanisms, and on account of the potential applications [1]. In many cases, the changes
to the chemical bonding or structure on the molecular level, which are caused by
a macroscopic mechanical stimulus, are responsible for the alternation of the properties of such MRL compounds [1, 2]. Several basic design concepts for mechanoresponsive luminescent materials have been proposed [1]. For example, Moore and
co-workers have developed mechano-responsive polymers by introducing segments
called mechanophores, whose chemical structures are very sensitive to the force that
is applied [1a]. Introducing flexible substituents in a rigid luminescent core represents another design strategy to achieve MRL properties, which has been reported by
Sagara and Kato for liquid crystalline materials [1c]. Focusing on crystalline MRL
© Springer Nature Singapore Pte Ltd. 2020
M. Jin, Novel Luminescent Crystalline Materials of Gold(I) Complexes
with Stimuli-Responsive Properties, Springer Theses,
https://doi.org/10.1007/978-981-15-4063-9_4
103