Department of Chemistry, Indian Institute of Technology, Indore 453552, India.
Department of Chemistry, Biology and Biotechnology, University of Perugia, via elce di sotto 8, 06123 Perugia, Italy.
J Am Chem Soc. 2021 Jul 7;143(26):9933-9943. doi: 10.1021/jacs.1c04173. Epub 2021 Jun 23.
A series of new naphthalimide and phenothiazine-based push-pull systems (), in which we structurally modulate the oxidation state of the sulfur atom in the thiazine ring, i.e., S(II), S(IV), and S(VI), was designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. The effect of the sulfur oxidation state on the spectral, photophysical, and electrochemical properties was investigated. The steady-state absorption and emission results show that oxygen functionalization greatly improves the optical (absorption coefficient and fluorescence efficiency) and nonlinear optical (hyperpolarizability) features. The cyclic voltammetry experiments and the quantum mechanical calculations suggest that phenothiazine is a stronger electron donor unit relative to phenothiazine-5-oxide and phenothiazine-5,5-dioxide, while the naphthalimide is a strong electron acceptor in all cases. The advanced ultrafast spectroscopic measurements, transient absorption, and broadband fluorescence up conversion give insight into the mechanism of photoinduced intramolecular charge transfer. A planar intramolecular charge transfer (PICT) and highly fluorescent excited state are populated for the oxygen-functionalized molecules and ; on the other hand, a twisted intramolecular charge transfer (TICT) state is produced upon photoexcitation of the oxygen-free derivatives and , with the fluorescence being thus significantly quenched. These results prove oxygen functionalization as a new effective synthetic strategy to tailor the photophysics of phenothiazine-based organic materials for different optoelectronic applications. While oxygen-functionalized compounds are highly fluorescent and promising active materials for current-to-light conversion in organic light-emitting diode devices, oxygen-free systems show very efficient photoinduced ICT and may be employed for light-to-current conversion in organic photovoltaics.
一系列新的萘酰亚胺和吩噻嗪基推拉系统（），其中我们在噻嗪环中结构调节硫原子的氧化态，即 S(II)、S(IV) 和 S(VI)，通过 Pd 催化的 Sonogashira 交叉偶联反应设计和合成。研究了硫氧化态对光谱、光物理和电化学性质的影响。稳态吸收和发射结果表明，氧官能化极大地提高了光学（吸收系数和荧光效率）和非线性光学（超极化率）特性。循环伏安实验和量子力学计算表明，吩噻嗪相对于吩噻嗪-5-氧化物和吩噻嗪-5,5-二氧化物是更强的电子给体单元，而萘酰亚胺在所有情况下都是强电子受体。先进的超快光谱测量、瞬态吸收和宽带荧光上转换深入了解了光致分子内电荷转移的机制。对于含氧分子和，存在平面分子内电荷转移（PICT）和高荧光激发态；另一方面，在氧自由衍生物和的光激发下产生扭曲分子内电荷转移（TICT）态，荧光因此显著猝灭。这些结果证明氧官能化是一种新的有效合成策略，可以调整基于吩噻嗪的有机材料的光物理性质，以适应不同的光电应用。虽然含氧化合物具有高荧光性，是有机发光二极管器件中电流到光转换的有前途的活性材料，但无氧系统表现出非常有效的光诱导 ICT，可用于有机光伏中的光到电流转换。
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