Sadowski Bartłomiej, Kaliszewska Marzena, Poronik Yevgen M, Czichy Małgorzata, Janasik Patryk, Banasiewicz Marzena, Mierzwa Dominik, Gadomski Wojciech, Lohrey Trevor D, Clark John A, Łapkowski Mieczysław, Kozankiewicz Bolesław, Vullev Valentine I, Sobolewski Andrzej L, Piatkowski Piotr, Gryko Daniel T
Institute of Organic Chemistry, Polish Academy of Sciences Kasprzaka 44/52 01-224 Warsaw Poland
Faculty of Chemistry, University of Warsaw Zwirki i Wigury 101 02-089 Warsaw Poland
Chem Sci. 2021 Sep 29;12(42):14039-14049. doi: 10.1039/d1sc03670j. eCollection 2021 Nov 3.
Nitroaromatics seldom fluoresce. The importance of electron-deficient (n-type) conjugates, however, has inspired a number of strategies for suppressing the emission-quenching effects of the strongly electron-withdrawing nitro group. Here, we demonstrate how such strategies yield fluorescent nitroaryl derivatives of dipyrrolonaphthyridinedione (DPND). Nitro groups near the DPND core quench its fluorescence. Conversely, nitro groups placed farther from the core allow some of the highest fluorescence quantum yields ever recorded for nitroaromatics. This strategy of preventing the known processes that compete with photoemission, however, leads to the emergence of unprecedented alternative mechanisms for fluorescence quenching, involving transitions to dark nπ* singlet states and aborted photochemistry. Forming nπ* triplet states from ππ* singlets is a classical pathway for fluorescence quenching. In nitro-DPNDs, however, these ππ* and nπ* excited states are both singlets, and they are common for nitroaryl conjugates. Understanding the excited-state dynamics of such nitroaromatics is crucial for designing strongly fluorescent electron-deficient conjugates.
硝基芳烃很少发荧光。然而，缺电子（n型）共轭物的重要性激发了一些抑制强吸电子硝基的发射猝灭效应的策略。在这里，我们展示了这些策略如何产生二吡咯并萘啶二酮（DPND）的荧光硝基芳基衍生物。DPND核心附近的硝基会猝灭其荧光。相反，离核心较远的硝基则能实现一些硝基芳烃有记录以来的最高荧光量子产率。然而，这种防止与光发射竞争的已知过程的策略，导致出现了前所未有的荧光猝灭替代机制，涉及向暗nπ单重态的跃迁和中止的光化学过程。从ππ单重态形成nπ三重态是荧光猝灭的经典途径。然而，在硝基-DPNDs中，这些ππ和nπ*激发态都是单重态，它们在硝基芳基共轭物中很常见。了解此类硝基芳烃的激发态动力学对于设计强荧光缺电子共轭物至关重要。
