A molecular crystal with an unprecedentedly long-lived photoexcited state. Issue 34 (18th July 2019)

• Record Type: Journal Article
• Authors: Naito, Toshio; Watanabe, Naoki; Sakamoto, Yuuka; Miyaji, Yuuko; Shirahata, Takashi; Misaki, Yohji; Kitou, Shunsuke; Sawa, Hiroshi
• Is Part Of: Dalton transactions. Volume 48:Issue 34(2019)
• Page Start: 12858
• Page End: 12866
• Publication Date: 2019-07-18
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c9dt02377a
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Gold(iii ) atoms reversibly deviate from the molecular plane on receiving thermal and photon energy. Abstract : The Au(iii )-complex anions in a newly synthesised compound BPY[Au(dmit)2 ]2 (BPY = N, N ′-ethylene-2, 2′-bipyridinium, dmit = 1, 3-dithiole-2-thione-4, 5-dithiolate) reversibly exhibit a molecular distortion in the solid state under UV-radiation. The photoexcited state is maintained for a week at 298 K, during which time molecules relax to their original structures and energy is gradually released as heat without decomposition or light emission. Most Au atoms adopt square planar (SP) coordination geometries, but some anions have unusual non-planar (NP) coordination geometries that produce disorder at the Au sites. The total (Gibbs) energy of the system depends on the proportion of Au atoms of NP geometry, which is directly determined from the occupancy (Occ (%)) by X-ray diffractometry. Due to phase transition, Occ substantially changes at a critical temperature ( T C ) of ∼280 K without other structural changes; however it remains almost constant in each phase. In addition, due to UV-promoted charge-transfer transitions between BPY and Au(dmit)2, Occ can be controlled by UV irradiation (∼250–450 nm). The UV-excited states have unprecedentedly long relaxation times ( t 1/2 > 36 h at 298 K), which is attributed to the close connection between the degrees of freedom on charge, spin, and molecular structures.