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Modulating Stepwise Photochromism in Platinum(II) Complexes with Dual Dithienylethene–Acetylides by a Progressive Red Shift of Ring-Closure Absorption

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journal contribution
posted on 04.11.2013, 00:00 by Bin Li, Hui-Min Wen, Jin-Yun Wang, Lin-Xi Shi, Zhong-Ning Chen
To modulate stepwise photochromism by shifting ring-closure absorption of the dithienylethene (DTE) moiety, trans-Pt­(PEt3)2(CC-DTE)2 [CC-DTE = L1o (1oo), L2o (2oo), L3o (3oo), and L4o (4oo)] and cis-Pt­(PEt3)2(L4o)2 (5oo) with two identical DTE–acetylides were elaborately designed. With the gradual red shift of ring-closure absorption for L1c (441 nm) → L2c (510 nm) → L3c (556 nm) → L4c (602 nm), stepwise photochromism is increasingly facilitated in trans-Pt­(PEt3)2(CC-DTE)2 following 1oo2oo3oo4oo. The conversion percentage of singly ring-closed 2co4co to dually ring-closed 2cc4cc at the photostationary state is progressively increased in the order 1cc (0%) → 2cc (18%) → 3cc (67%) → 4cc (100%). Compared with trans-arranged 4oo, stepwise photochromism in the corresponding cis-counterpart 5oo is less pronounced, ascribed to either direct conversion of 5oo to 5cc or rapid conversion of 5co to 5cc. The progressively facile stepwise photocyclization following 2oo3oo4oo is reasonably interpreted by gradually enhanced transition character involving LUMO+1, which is the only unoccupied frontier orbital responsible for further photocyclization of singly ring-closed 2co4co.