The nonradiative decay mechanism of dinuclear iridium complexes: a density functional theory study.

Dinuclear metal complexes are a promising class of compounds applicable to photoluminescence and catalysis. However, an understanding of the mechanism of the nonradiative decay process of dinuclear metal complexes remains very limited. Herein, the mechanism of the nonradiative decay process of dinuclear iridium(III) complexes (D1 and D2) and their mononuclear iridium(III) complex (M1) is elucidated by using density functional theory (DFT). Our results reveal that the nonradiative decay process occurs on a weak Ir-N bond and therefore results in metal-centered triplet excited (3MC) states. The deactivation pathways connecting the Franck-Condon region and the minimum energy seam of crossing (MESX) were further identified to be the determining step, which is the thermal deactivation pathways of 3MLCT → TS → 3MC→ MESX. The smaller energy barrier from the T1 minimum to the MESX state for D1 (9.48 kcal mol-1) and D2 (8.64 kcal mol-1) relative to that for M1 (10.95 kcal mol-1) plays a key role in observed weak emissions of D1 and D2 in the red region compared to that of M1. Moreover, by introducing the electron-withdrawing Cl atom at the para- or meta-position of the 2-phenylpyrimidine (ppd) moiety, a large energy barrier between the 3MC state and the T1 minimum is obtained. Our work not only provides the possibility of the nonradiative decay process of dinuclear iridium(III) materials, but also paves a promising way for reducing the nonradiative process and developing saturated efficient red dinuclear iridium(III) materials for broader potential application.

Characteristic Aroma Components from Dried "Wakame" Undaria pinnatifida.

An essential oil from dried "wakame" (Undaria pinnatifida), prepared by a simultaneous distillation extraction method, was analyzed by GC-MS, indicating the presence of one major component of volatiles. The volatile component was identified as (6Z,9Z,12Z,15Z,18Z)-1,6,9,12,15,18-henicosahexaene by comparison with the GC-MS and NMR spectra of synthetic. The henicosahexaene showed a subtly marine aroma. (6Z,9Z,12Z,15Z)-1,6,9,12,15-Henicosapentaene was also detected as a minor polyene in the essential oils. It was suggested that these polyenes contribute to the characteristic aroma of the dried wakame.

Two Types of Volatile Polyenes in the Brown Alga Sargassum thunbergii.

An essential oil from the brown alga Sargassum thunbergii, prepared by a simultaneous distillation extraction method, contained in two types of volatile polyenes with a terminal double bond such as (6Z,9Z,12Z,15Z,18Z)-1,6,9,12,15,18-henicosahexaene and (6Z,9Z,12Z,15Z)-1,6,9,12,15-henicosapentaene and with their saturated terminal structures such as (3Z,6Z,9Z,12Z,15Z,18Z)-3,6,9,12,15,18-henicosahexaene and (3Z,6Z,9Z,12Z,15Z)-3,6,9,12,15-henicosapentaene. These volatile polyenes were identified by comparison with the GC-MS and NMR spectra of synthetics. The polyenes with the saturated terminal structures were found in the brown algae for the first time.