136
5 Mechanical-Stimulation-Triggered and Solvent-Vapor-Induced …
In order to obtain mechanistic insights into the emission properties of 3G/MeOH
and 3O scsc , we carried out time-dependent (TD) DFT calculations on the singlecrystal structures. The tetramer geometry of 3G/MeOH was thereby adopted from
the crystal structure of 3O scsc . The simulated UV-vis absorption spectra were similar
to the excitation spectra of both crystals, thus suggesting a reasonable excitation
path for both samples (Fig. 5.25). The HOMOs of both 3G/MeOH and 3O scsc are
localized on the gold atoms, forming aurophilic interactions, and the LUMOs are
mainly located on the isocyanide ligands (Fig. 5.26). These results demonstrate the
metal-metal-to-ligand charge transfer (MMLCT) character (from the gold atoms to
the isocyanide ligands) of the excited states of 3G/MeOH and 3O scsc . For many
arylgold(I) isocyanide complexes, polymorphs with smaller θ ph-ph values show a
red-shifted emission compared to those with larger θ ph-ph values [9]. The structures
of 3G/MeOH and 3O scsc obtained in this work are thus consistent with this trend
(3G/MeOH: λ em,max = 506 nm, θ ph-ph = 83.12°; 3O scsc : λ em,max = 612 nm, θ ph-ph
= 33.03°). The long emission lifetimes (14.6 and 331.1 μs) suggest that solid-state
luminescence occurs from the triplet excited state. It would thus be feasible to assume
that the structure relaxation during the excitation-emission process should cause the
red-shifted emission of 3O relative to that of 3G/MeOH.
5.5 Control Experiment and Proposed Mechanism
of the Reversible SCSC
The reversion of 3O into 3G/MeOH depends on the crystal preparation procedure.
The phase transition from 3G/MeOH to 3O scsc was also observed when the crystal
was gently heated at 30 °C under ambient atmosphere to release the MeOH molecules.
The reversion of this heated sample was then confirmed by exposure to high concentrations of MeOH vapor at room temperature (Fig. 5.19). The orange-emitting crystal
3O was prepared by recrystallization from CH 2 Cl 2 and hexane (instead of MeOH),
and its crystal structure was confirmed to match that of 3O scsc (Fig. 5.19). In contrast to 3O scsc , the resulting crystal did not exhibit a phase transition into 3G/MeOH
upon exposure to saturated MeOH vapor or addition of liquid MeOH (Fig. 5.20).
An orange-emitting sample of a crystalline powder, which was obtained from ballmilling 3G/MeOH (Figs. 5.21, 5.22, and 5.23), exhibited a crystal structure similar
to that of 3O scsc , which was confirmed by powder XRD analysis (Fig. 5.23). Changes
of the emission color into the green were not observed for this powder sample upon
exposure to saturated MeOH vapor (Figs. 5.21, 5.22, and 5.23). The resulting orangeemitting sample of a crystalline powder showed an emission change to yellow under
concomitant formation of a distinct crystalline structure, which is not consistent with
that of 3G/MeOH, as evident from the powder XRD analysis (Fig. 5.21, 5.22, and
5.23). SEM images of 3O scsc and 3O samples obtained from different procedures
indicate their distinct surface characteristics (Fig. 5.24). The crystal 3O scsc had rough
5 Mechanical-Stimulation-Triggered and Solvent-Vapor-Induced …
In order to obtain mechanistic insights into the emission properties of 3G/MeOH
and 3O scsc , we carried out time-dependent (TD) DFT calculations on the singlecrystal structures. The tetramer geometry of 3G/MeOH was thereby adopted from
the crystal structure of 3O scsc . The simulated UV-vis absorption spectra were similar
to the excitation spectra of both crystals, thus suggesting a reasonable excitation
path for both samples (Fig. 5.25). The HOMOs of both 3G/MeOH and 3O scsc are
localized on the gold atoms, forming aurophilic interactions, and the LUMOs are
mainly located on the isocyanide ligands (Fig. 5.26). These results demonstrate the
metal-metal-to-ligand charge transfer (MMLCT) character (from the gold atoms to
the isocyanide ligands) of the excited states of 3G/MeOH and 3O scsc . For many
arylgold(I) isocyanide complexes, polymorphs with smaller θ ph-ph values show a
red-shifted emission compared to those with larger θ ph-ph values [9]. The structures
of 3G/MeOH and 3O scsc obtained in this work are thus consistent with this trend
(3G/MeOH: λ em,max = 506 nm, θ ph-ph = 83.12°; 3O scsc : λ em,max = 612 nm, θ ph-ph
= 33.03°). The long emission lifetimes (14.6 and 331.1 μs) suggest that solid-state
luminescence occurs from the triplet excited state. It would thus be feasible to assume
that the structure relaxation during the excitation-emission process should cause the
red-shifted emission of 3O relative to that of 3G/MeOH.
5.5 Control Experiment and Proposed Mechanism
of the Reversible SCSC
The reversion of 3O into 3G/MeOH depends on the crystal preparation procedure.
The phase transition from 3G/MeOH to 3O scsc was also observed when the crystal
was gently heated at 30 °C under ambient atmosphere to release the MeOH molecules.
The reversion of this heated sample was then confirmed by exposure to high concentrations of MeOH vapor at room temperature (Fig. 5.19). The orange-emitting crystal
3O was prepared by recrystallization from CH 2 Cl 2 and hexane (instead of MeOH),
and its crystal structure was confirmed to match that of 3O scsc (Fig. 5.19). In contrast to 3O scsc , the resulting crystal did not exhibit a phase transition into 3G/MeOH
upon exposure to saturated MeOH vapor or addition of liquid MeOH (Fig. 5.20).
An orange-emitting sample of a crystalline powder, which was obtained from ballmilling 3G/MeOH (Figs. 5.21, 5.22, and 5.23), exhibited a crystal structure similar
to that of 3O scsc , which was confirmed by powder XRD analysis (Fig. 5.23). Changes
of the emission color into the green were not observed for this powder sample upon
exposure to saturated MeOH vapor (Figs. 5.21, 5.22, and 5.23). The resulting orangeemitting sample of a crystalline powder showed an emission change to yellow under
concomitant formation of a distinct crystalline structure, which is not consistent with
that of 3G/MeOH, as evident from the powder XRD analysis (Fig. 5.21, 5.22, and
5.23). SEM images of 3O scsc and 3O samples obtained from different procedures
indicate their distinct surface characteristics (Fig. 5.24). The crystal 3O scsc had rough