Photochromic properties of ruthenium complexes with dithienylethene-ethynylthiophene

Abstract

In order to extend stepwise photochromism to more metal-coordination systems for multicolors and multistates, a new photochromic dithienylethene-ethynylthiophene (L1o) was synthesized to design head–head coupled symmetric ruthenium(II) complex trans-Ru(dppe)2(L1o)2 (1oo) and head-shoulder coupled asymmetric ruthenium(II) complex trans-Ru(dppe)2(L1o)(L2o) (2oo). However, upon irradiation under UV light, 1oo only converts to 1co without the observation of dually ring-closed species 1cc, and only the dually ring-closed species 2cc is observed without the detection of the mixed ring-open/closed species 2co and 2oc, implying that it is difficult to achieve substantial stepwise photochromic process of 1oo-2oo → 1co-2oc/2co→1cc-2cc due to the rapid intramolecular energy transfer in 1co and the absence of electronic communication between two dithienylethene units in 2oo. The photochemical processes are well demonstrated and explained by NMR, UV–vis, electrochemical, as well as time-dependent density functional theory (TD-DFT) computational studies.