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

• Published in: Journal of the American Chemical Society Vol. 139; no. 4; pp. 1636 - 1644
• Main Authors: Chen, Wei, Chen, Chi-Lin, Zhang, Zhiyun, Chen, Yi-An, Chao, Wei-Chih, Su, Jianhua, Tian, He, Chou, Pi-Tai
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 01.02.2017; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; RED; ELECTRON-TRANSFER; FLUORESCENCE; LARGE STOKES SHIFT; SYSTEMS; CHARGE-TRANSFER; EXCIPLEX
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.6b11789

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.