5.1 Introduction
129
was the only way to recover the original polymorph [5a–d]. Some mechanically
responsive crystalline materials exhibit a self-healing behavior through SCSC phase
transitions [5e, 6]. However, the phenomenon is still rare and unknown in the fields
of mechano-responsive luminescent crystalline materials.
Herein, the first example of a mechanical-stimulation-triggered SCSC transition
under a concomitant change of the emission color and reversion through exposure
to solvent vapors is described. Gold(I) complex 3 crystallizes under the inclusion
of MeOH solvate molecules, and exhibits a molecular domino-type SCSC phase
transition upon mechanical stimulation (cutting) that is accompanied by a drastic
color change of the luminescence from green to orange under concomitant release
of MeOH from the crystal (Fig. 5.1b). Remarkably, the resulting daughter phase can
be reversed into the original phase in an SCSC manner upon exposure to a saturated
MeOH vapor environment (Fig. 5.1b).
5.2 Synthesis and Preparation
Gold(I) isocyanide complex 3 was prepared according to a previously described
procedure [7]. A recrystallization from CH 2 Cl 2 and MeOH afforded needle-shaped
crystals of 3G/MeOH (Fig. 5.2a). The green emission of the 3G/MeOH crystals
did not change in a vial or a petri dish saturated with MeOH vapor (cf. the experimental section and Fig. 5.6). However, an orange emission was observed when the
3G/MeOH crystals were transferred to a glass plate under ambient atmosphere at
room temperature (Fig. 5.6). The resulting orange-emitting crystal showed no further
emission change upon mechanical stress such as cutting or grinding.
However, even under MeOH vapor, a change of the emission color from green
to orange was triggered by mechanical stimulation. As shown in Fig. 5.2a, a single
thin crystal of 3G/MeOH was placed on a glass plate at 22 °C in an open petri dish
that contained MeOH vapor (for details, see Figs. 5.6 and 5.7). The crystal was then
cut using a small knife (Fig. 5.2b, c), after which the emission color changed to
orange at the affected cross-sections (Fig. 5.2d). Subsequently, the domain of the
crystal exhibiting orange emission gradually expanded. After ca. 40 min, the entire
crystal exhibited orange emission, denoted here as 3O scsc (Fig. 5.2d–e). Crystals in
the same dish that were not cut did not show a change of the emission color when
3O scsc spontaneously appeared. Interestingly, a reversion of the emission of 3O scsc to
the original green color, similar to that of 3G/MeOH, was observed upon exposing
3O scsc to saturated MeOH vapor by putting a lid on the petri dish (Fig. 5.2j). After ca.
15 min, the crystals had reverted entirely to the original phase, denoted as 3G re /MeOH
(Fig. 5.2f–i). The recovered crystal fragments moreover displayed the same emission
change to orange after cutting them under low concentrations of MeOH vapor.
129
was the only way to recover the original polymorph [5a–d]. Some mechanically
responsive crystalline materials exhibit a self-healing behavior through SCSC phase
transitions [5e, 6]. However, the phenomenon is still rare and unknown in the fields
of mechano-responsive luminescent crystalline materials.
Herein, the first example of a mechanical-stimulation-triggered SCSC transition
under a concomitant change of the emission color and reversion through exposure
to solvent vapors is described. Gold(I) complex 3 crystallizes under the inclusion
of MeOH solvate molecules, and exhibits a molecular domino-type SCSC phase
transition upon mechanical stimulation (cutting) that is accompanied by a drastic
color change of the luminescence from green to orange under concomitant release
of MeOH from the crystal (Fig. 5.1b). Remarkably, the resulting daughter phase can
be reversed into the original phase in an SCSC manner upon exposure to a saturated
MeOH vapor environment (Fig. 5.1b).
5.2 Synthesis and Preparation
Gold(I) isocyanide complex 3 was prepared according to a previously described
procedure [7]. A recrystallization from CH 2 Cl 2 and MeOH afforded needle-shaped
crystals of 3G/MeOH (Fig. 5.2a). The green emission of the 3G/MeOH crystals
did not change in a vial or a petri dish saturated with MeOH vapor (cf. the experimental section and Fig. 5.6). However, an orange emission was observed when the
3G/MeOH crystals were transferred to a glass plate under ambient atmosphere at
room temperature (Fig. 5.6). The resulting orange-emitting crystal showed no further
emission change upon mechanical stress such as cutting or grinding.
However, even under MeOH vapor, a change of the emission color from green
to orange was triggered by mechanical stimulation. As shown in Fig. 5.2a, a single
thin crystal of 3G/MeOH was placed on a glass plate at 22 °C in an open petri dish
that contained MeOH vapor (for details, see Figs. 5.6 and 5.7). The crystal was then
cut using a small knife (Fig. 5.2b, c), after which the emission color changed to
orange at the affected cross-sections (Fig. 5.2d). Subsequently, the domain of the
crystal exhibiting orange emission gradually expanded. After ca. 40 min, the entire
crystal exhibited orange emission, denoted here as 3O scsc (Fig. 5.2d–e). Crystals in
the same dish that were not cut did not show a change of the emission color when
3O scsc spontaneously appeared. Interestingly, a reversion of the emission of 3O scsc to
the original green color, similar to that of 3G/MeOH, was observed upon exposing
3O scsc to saturated MeOH vapor by putting a lid on the petri dish (Fig. 5.2j). After ca.
15 min, the crystals had reverted entirely to the original phase, denoted as 3G re /MeOH
(Fig. 5.2f–i). The recovered crystal fragments moreover displayed the same emission
change to orange after cutting them under low concentrations of MeOH vapor.