Highly Efficient Aggregation-Induced Room-Temperature Phosphorescence with Extremely Large Stokes Shift Emitted from Trinuclear Gold(I) Complex Crystals

Highly efficient (≈75% quantum yield), aggregation-induced phosphorescence is reported. The phosphorescence is emitted at room temperature and in the presence of air from crystals of trinuclear Au(I) complexes, accompanied by an extremely large Stokes shift of 2.2 × 104 cm−1 (450 nm). The mechanism of the aggregation-induced room-temperature phosphorescence from the Au complex crystals was investigated in terms of the crystal packing structure and the primary structure of the molecules. It was found that two kinds of intermolecular interactions occurred in the crystals, and that these multiple dual-mode intermolecular interactions in the crystals play a crucial role in the in-air room-temperature phosphorescence of the trinuclear Au(I) complexes.


Preparation of Materials.
The synthetic route for preparation of trinuclear Au(I) complexes (DTn) is shown in Scheme S1.
[1] Unless otherwise noted, all solvents and reagents were purchased from commercial suppliers and were used without further purification. 1 H NMR spectra were recorded on a JEOL ECS-400 spectrometer at 400 MHz using the residual proton in the NMR solvent as an internal reference. The complex DT6 was first synthesized in this study, and were fully characterized by high-resolution mass spectroscopy (HRMS), infrared spectroscopy (IR), and elemental analysis. Electrospray ionization mass spectra (ESI-MS) were measured on JMS-T1000LC (JEOL). IR spectra were recorded on a JASCO FT/IR-4100 spectrometer using a KBr pellet. The melting points of the final products were determined at the peaks onset of differential scanning calorimetry (DSC) with heating and cooling rates at 1.0 °C/min. Scheme S1. Synthetic route of DTn (n = 6-8)

Synthesis of (tht)AuCl
Tetrachloroauric(III) acid (1.0 g, 2.5 mmol) in 1.3 mL of water was added to 7.8 mL of ethanol and stirred at room temperature. To the resultant solution, 0.44 mL (4.9 mmol) of tetrahydrothiophene was added slowly, stirred at room temperature for 2 h, and then white precipitate was appeared. The precipitate was collected by filtration, washed with small amount of ethanol and air-dried to give 0.77 g (2.4 mmol) of white solid ((tht)AuCl) in 96% yield. 1

Single Crystal X-Ray Structure Analysis.
The molecular structure and crystal packing structure were determined by single crystal X-ray structural analysis. Single crystals of Au(I) complexes were obtained by slow evaporation from a mixed solvent system (dichloromethane/acetone). Each crystal was mounted on a glass fiber and the omega scanning technique was used to collect the reflection data using a Bruker D8 goniometer with monochromatic Mo Kα radiation (λ = 0.71075 Å) for DT6 or a Rigaku automated four-circular-axis diffractometer AFC-5R with graphite monochromatized Cu Kα radiation (λ = 1.54178 Å) for DT7 and DT8. To investigate the actual crystal structure of in-use materials, the measurements were performed at ambient temperature (296 K).
For DT6, the initial structure of each unit cell was determined using a direct method in APEX3. The structural models were refined using a full-matrix least squares method in SHELXL-2014/6.[2] All calculations were performed using SHELXL programs.
For DT7 and DT8, the initial structure in the unit cell was determined by a direct method using SIR92. [3] The structure model was refined by full-matrix least-squares methods using SHELXL97.
[2b] All calculations were performed on the crystallographic software package WinGX. [4] The crystal data for complexes are summarized in Table S1. When alkyl chains were disordered, the occupancy of atoms was separated to two parts. The data in Table S1 have been indexed and are included in the Cambridge Crystallographic Data Center (CCDC) database with the following reference numbers of CCDC 1910566 for DT6, 1910567 for DT7, and 1910568 for DT8. The indexed database contains additional supplementary crystallographic data for this paper and may be accessed without charge at http://www.ccdc.cam.ac.uk/conts/retrieving.html. Complexes DT7 and DT8, which have been already synthesized and characterized by Kim et al., [1] showed the same structure as reported. The molecular structure and packing structure for DT7 and DT8 are shown in Figure S4 and S5.

TD-DFT calculations
The TD-DFT calculations were performed for DT6 as a representative example using the Gaussian 03 (revision E.01) program package, employing B3LYP hybrid functionals with SDD (for the Au atoms) and 6-311+G (d,p) (for the other atoms) basis sets. [5] The single point energy calculation was carried out for the dimer of DT6 formed in the crystal using the conformation obtained from the X-ray crystallography results. The vertical excitation energies and oscillator strengths were estimated for the 8 lowest transitions to excited singlets and are listed below.