Fluorophores with intramolecular charge-transfer (ICT) character in the excited state exhibit significant solvatochromism of their fluorescence. Here, we report an example for such compounds, a benzophosphole P-oxide bearing an electron-donating p-(diphenylamino)phenyl group at the 3-position. While this compound shows only subtle dependence of the absorption maximum on the solvent polarity (λmax = 383–392 nm), its emission maximum is significantly red-shifted upon increasing the solvent polarity (cyclohexane: λem = 457 nm; DMF: λem = 598 nm). Most notably, the fluorescence quantum yields gradually increase with increased Stokes shifts, ultimately reaching ΦF = 0.28 in DMF. This trend is fundamentally different from that observed for the corresponding 2-(diphenylamino)phenyl-substituted benzophosphole congener, for which applications as a fluorescent bioimaging probe were previously demonstrated. In this study, the origins of this striking difference are examined by a combined experimental and theoretical approach. Our results suggest that the observed difference arises from a significant contribution of quinoidal resonance forms in the ICT excited state, which suppresses nonradiative decay and hence increases the quantum yield in polar solvents.
Benzo[<i>b</i>]phosphole-Containing π-Electron Systems: Synthesis Based on an Intramolecular<i>trans</i>-Halophosphanylation and Some Insights into Their Properties
wavelengths. The intrinsic substituent effects of the phosphoryl group in this skeleton are to decrease the oscillator strength of the electronic transition and thus decrease the radiative decayrate constants from the singlet excited state. Nevertheless, these compounds maintain high fluorescence quantum yields (ΦF>0.8) owing to the significantly retarded nonradiativedecay process. In the study of the benzodiphosphole
PBr 3介导的2-(氨基膦酰基)苯基乙炔分子内反式-卤代膦酰基化反应,再用H 2 O 2氧化,生成3-溴代苯并[ b ]氧化膦衍生物。通过在LiI存在下进行反应,这种环化反应也可用于合成3-碘衍生物。在此基础上合成的方法中,各种含benzophosphole-π共轭系化合物,其中磷和亚甲基桥连的二苯乙烯10,2,3,6,7- tetraphenylbenzo [1,2 b:4,5- b '] diphosphole- P, P'-二氧化物11及其硫化膦衍生物12是合成的。在一系列的桥接茋的,包括双(亚甲基)-bridged茋结构-性能关系的研究10,和双(磷酰基)-bridged茋,揭示了作为磷酰基的贡献增加,吸收发射最大值基本上转移到更长的波长。该骨架中磷酰基的固有取代基作用是降低电子跃迁的振荡强度,从而降低来自单重态激发态的辐射衰减速率常数。然而,这些化合物保持高荧光量子产率(Φ ˚F由于显著延迟非辐射的衰变过程>