Theoretically exploring the luminescence mechanism tuned by intermolecular weak interactions of a mechanochromic 9-anthryl gold(I) isocyanide complex

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2020-02, Vol.388, p.112195, Article 112195
• Main Authors: Gu, Hao-Yu, Gao, Ying, Duan, Ying-Chen, Geng, Yun, Zhao, Liang, Zhang, Min, Wu, Yong
• Format: Article
• Language: English
• Subjects: anti-Kasha rule; Intermolecular weak interactions; Luminescence mechanism; Mechanochromic; QM/MM
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2019.112195

The luminescence mechanism of a mechanochromic 9-anthryl gold(I) isocyanide complex was focused on, which involves the complicated discussion on the sensitive relationships among molecule structure, multiple intermolecular interactions and photophysical processes. [Display omitted] •The difference in geometric structures of α and β induces the conversion from fluorescence to phosphorescence.•The intermolecular weak interactions can affect the photophysical properties of the polymorphs.•The α crystal phase exhibits fluorescence arising from S2 state, which breaks the Kasha’s rule.•The aurophilic interaction is mainly responsible for the red-shifted luminescence of the γ dimer. An interesting luminescent mechanochromic 9-anthryl gold(I) isocyanide complex has been reported. Its polymorphs perform different luminescent properties and their luminescence spectra are both bathochromically shifted upon grinding. This curious phenomenon arouses our interest to disclose how intermolecular weak interactions tune the luminescent properties from a theoretical perspective. The QM/MM approach was employed through all the calculations to consider the sensitive dependence of geometric and electronic structures on intermolecular interactions. The results show that the monomer is enough to describe the fluorescence of α phase crystal and its almost perpendicular dihedral angle between anthracene unit and phenyl ring leads to the forbidden emission from the first excited state which breaks Kasha’s rule. While the larger spin orbital coupling between excited singlet and triplet states of dimer makes key contribution to the phosphorescence emission of β phase crystal which is related with its near planar structure and stronger intermolecular interactions. Moreover, multiple intermolecular interactions including strong aurophilic interaction were found to be responsible for the red-shifted luminescence of the γ phase crystal. Therefore, the distinct molecular structures and intermolecular interactions codetermine the different photophysical processes in these crystal phases.