State Key Laboratory of Fine Chemicals, Dalian University of Technology , 2 Linggong Road, Dalian 116024, People's Republic of China.
J Am Chem Soc. 2014 Jul 9;136(27):9590-7. doi: 10.1021/ja502292p. Epub 2014 Jun 26.
Compared with fluorescence imaging utilizing fluorophores whose lifetimes are in the order of nanoseconds, time-resolved fluorescence microscopy has more advantages in monitoring target fluorescence. In this work, compound DCF-MPYM, which is based on a fluorescein derivative, showed long-lived luminescence (22.11 μs in deaerated ethanol) and was used in time-resolved fluorescence imaging in living cells. Both nanosecond time-resolved transient difference absorption spectra and time-correlated single-photon counting (TCSPC) were employed to explain the long lifetime of the compound, which is rare in pure organic fluorophores without rare earth metals and heavy atoms. A mechanism of thermally activated delayed fluorescence (TADF) that considers the long wavelength fluorescence, large Stokes shift, and long-lived triplet state of DCF-MPYM was proposed. The energy gap (ΔEST) of DCF-MPYM between the singlet and triplet state was determined to be 28.36 meV by the decay rate of DF as a function of temperature. The ΔE(ST) was small enough to allow efficient intersystem crossing (ISC) and reverse ISC, leading to efficient TADF at room temperature. The straightforward synthesis of DCF-MPYM and wide availability of its starting materials contribute to the excellent potential of the compound to replace luminescent lanthanide complexes in future time-resolved imaging technologies.
与利用荧光团的荧光寿命在纳秒量级的荧光成像相比，时间分辨荧光显微镜在监测靶标荧光方面具有更多优势。在这项工作中，基于荧光素衍生物的化合物 DCF-MPYM 表现出长寿命发光（在去氧乙醇中为 22.11 μs），并用于活细胞中的时间分辨荧光成像。纳秒时间分辨瞬态差分吸收光谱和时间相关单光子计数（TCSPC）都被用来解释该化合物的长寿命，这在没有稀土金属和重原子的纯有机荧光团中很少见。提出了一种考虑 DCF-MPYM 的长波长荧光、大斯托克斯位移和长寿命三重态的热激活延迟荧光（TADF）机制。通过 DF 的衰减率随温度的变化来确定 DCF-MPYM 的单重态和三重态之间的能隙（ΔEST）为 28.36 meV。ΔE（ST）足够小，允许有效的系间穿越（ISC）和反向 ISC，从而在室温下实现有效的 TADF。DCF-MPYM 的合成路线简单，其起始原料广泛可得，这使得该化合物具有取代未来时间分辨成像技术中发光镧系配合物的优异潜力。
