Snapshotting the Excited-State Planarization of Chemically Locked N,N′-Disubstituted Dihydrodibenzo[a,c]phenazines

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• 作者：Wei Chen ; Chi-Lin Chen ; Zhiyun Zhang ; Yi-An Chen ; Wei-Chih Chao ; Jianhua Su ; He Tian ; Pi-Tai Chou
• 刊名：Journal of the American Chemical Society
• 出版年：2017
• 出版时间：February 1, 2017
• 年：2017
• 卷：139
• 期：4
• 页码：1636-1644
• 全文大小：692K
• ISSN：1520-5126

文摘

For deeper understanding of the coupling of electronic processes with conformational motions, we exploit a tailored strategy to harness the excited-state planarization of N,N′-disubstituted dihydrodibenzo[a,c]phenazines by halting the structural evolution via a macrocyclization process. In this new approach, 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) is used as a prototype, in which the para sites of 9,14-diphenyl are systematically enclosed by a dialkoxybenzene-alkyl-ester or -ether linkage with different chain lengths, imposing various degrees of constraint to impede the structural deformation. Accordingly, a series of DPAC-n (n = 1–8) derivatives were synthesized, in which n correlates with the alkyl length, such that the strength of the spatial constraint decreases as n increases. The structures of DPAC-1, DPAC-3, DPAC-4, and DPAC-8 were identified by the X-ray crystal analysis. As a result, despite nearly identical absorption spectra (onset ∼400 nm) for DPAC-1–8, drastic chain-length dependent emission is observed, spanning from blue (n = 1, 2, ∼400 nm) and blue-green (n = 3–5, 500–550 nm) to green-orange (n = 6) and red (n = 7, 8, ∼610 nm) in various regular solvents. Comprehensive spectroscopic and dynamic studies, together with a computational approach, rationalized the associated excited-state structure responding to emission origin. Severing the linkage for DPAC-5 via lipase treatment releases the structural freedom and hence results in drastic changes of emission from blue-green (490 nm) to red (625 nm), showing the brightening prospect of these chemically locked DPAC-n in both fundamental studies and applications.