174
6 Thermo-Responsive Phosphorescence Control Mediated …
energetics of molecular orbitals, which in turn may also alter excitation energies
and emission properties [7]. We found upon inspection of the XRD structures that
changes in the Au–Au distances in the range of 193–298 K for 1 and 2 are not
sufficient to explain the different trends in their corresponding emission properties
(Fig. 6.18). The Au–Au distances of 1 and 2 increased upon heating to 298 K, and
their corresponding changes were 0.042 and 0.054 Å, respectively, with a greater
change observed for the complex that presents no changes in emission. Based on
these observations, we conclude that the phosphorescence changes upon cooling and
heating are not correlated with aurophilic interactions but are more likely the result
changes in electronic communication that occur when the central phenylene vibrates
and rotates in the crystal.
6.8 Summary
In this work, we described the first example of a crystalline material where changes
in phosphorescence appear to be the result of changes in the rotational motion of an
aromatic chromophore that is part of dumbbell-shaped gold(I) complex 1. Changes
in emission properties and rotational frequency exhibited a reasonable correlation,
and TD-DFT studies revealed that conformational changes of the phenylene rotator
can cause changes in the electronic communication between adjacent chromophores.
Furthermore, gold(I) complex 2 with a sterically hindered tetramethylphenylene rotator provided us with an excellent control sample where no changes in emission color
and no rotational motion can be detected in its crystals. These results strongly indicate
that the luminescence properties of bulk materials can be tuned by taking advantage
of amphidynamic crystals that allow for structurally-controlled rotational motion.
6.9 Experimental Section
6.9.1 General
All commercially available reagents and solvents are reagent grade and were used
without further purification unless otherwise noted. Solvents for the synthesis were
purchased from commercial suppliers, degassed by three freeze-pump-thaw cycles
and further dried over molecular sieves (4 Å). NMR spectra were recorded on a JEOL
JNM-ECX400P or JNM-ECS400 spectrometer (
1 H: 400 MHz;
13 C: 99.5 MHz) using
tetramethylsilane and CDCl 3 as internal standards, respectively. Solid-state NMR
spectra were acquired on a Bruker DRX 300 instrument (
2 H: 46.07 MHz;
13 C:
75.47 MHz). Emission spectra were recorded on a Hitachi F-7000 spectrometer.
Absorption spectra were recorded on the basis of synchronous fluorescence spectroscopy using a Hitachi F-7000 spectrometer equipped with an integrating sphere.
6 Thermo-Responsive Phosphorescence Control Mediated …
energetics of molecular orbitals, which in turn may also alter excitation energies
and emission properties [7]. We found upon inspection of the XRD structures that
changes in the Au–Au distances in the range of 193–298 K for 1 and 2 are not
sufficient to explain the different trends in their corresponding emission properties
(Fig. 6.18). The Au–Au distances of 1 and 2 increased upon heating to 298 K, and
their corresponding changes were 0.042 and 0.054 Å, respectively, with a greater
change observed for the complex that presents no changes in emission. Based on
these observations, we conclude that the phosphorescence changes upon cooling and
heating are not correlated with aurophilic interactions but are more likely the result
changes in electronic communication that occur when the central phenylene vibrates
and rotates in the crystal.
6.8 Summary
In this work, we described the first example of a crystalline material where changes
in phosphorescence appear to be the result of changes in the rotational motion of an
aromatic chromophore that is part of dumbbell-shaped gold(I) complex 1. Changes
in emission properties and rotational frequency exhibited a reasonable correlation,
and TD-DFT studies revealed that conformational changes of the phenylene rotator
can cause changes in the electronic communication between adjacent chromophores.
Furthermore, gold(I) complex 2 with a sterically hindered tetramethylphenylene rotator provided us with an excellent control sample where no changes in emission color
and no rotational motion can be detected in its crystals. These results strongly indicate
that the luminescence properties of bulk materials can be tuned by taking advantage
of amphidynamic crystals that allow for structurally-controlled rotational motion.
6.9 Experimental Section
6.9.1 General
All commercially available reagents and solvents are reagent grade and were used
without further purification unless otherwise noted. Solvents for the synthesis were
purchased from commercial suppliers, degassed by three freeze-pump-thaw cycles
and further dried over molecular sieves (4 Å). NMR spectra were recorded on a JEOL
JNM-ECX400P or JNM-ECS400 spectrometer (
1 H: 400 MHz;
13 C: 99.5 MHz) using
tetramethylsilane and CDCl 3 as internal standards, respectively. Solid-state NMR
spectra were acquired on a Bruker DRX 300 instrument (
2 H: 46.07 MHz;
13 C:
75.47 MHz). Emission spectra were recorded on a Hitachi F-7000 spectrometer.
Absorption spectra were recorded on the basis of synchronous fluorescence spectroscopy using a Hitachi F-7000 spectrometer equipped with an integrating sphere.