Green-emitting Polyfluorenes Containing Hexylthiophen-dibenzothiophene-S,S-dioxide Unit with Large Two-photon Absorption Cross Section

Enhanced Two-Photon Fluorescence and Fluorescence Imaging of Novel Probe for Calcium Ion by Self-Assembly with Conjugated Polymer

The calcium ion (Ca2+) isa highly versatile intracellular signal messenger regulating many different cellular functions. It is important to design probes with good fluorescence and two-photon (TP) active cross-sections (Φδ) to explore the concentration distribution of Ca2+. In this manuscript, a novel TP fluorescence calcium probe (BAPTAVP) with positive charges, based on the classical Ca2+ indicator of BAPTA (1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetra acetic acid), and a conjugated polymer (PCBMB) with negative charges were designed and synthesized. The results from transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and the zeta potential (ZP) showed that nanoparticles were obtained by the self-assembly of PCBMB and BAPTAVP. Moreover, the fluorescence properties of BAPTAVP were effectively improved by fluorescence resonance energy transfer (FRET) with PCBMB and attenuating the intramolecular charge transfer (ICT) after the addition of Ca2+. The quantum yield and Φδ of PCBMB-BAPTAVP increased by about four and six times in comparison to those of BAPTAVP, respectively. The TP fluorescence imaging experiments indicated that the PCBMB-BAPTAVP system could effectively detect Ca2+ in living cells with high sensitivity.

Bromine-Substituted Fluorene: Molecular Structure, Br-Br Interactions, Room-Temperature Phosphorescence, and Tricolor Triboluminescence

Organic tribophosphorescence materials are rarely reported and the introduction of Br atoms may be a practical way to design such materials. Here four bromine-substituted fluorene-based derivatives are presented and BrFlu-CBr, having fluorescence-phosphorescence dual-emission induced not only by UV light but also by mechanical stimulus, manifests the highest phosphorescence efficiency of 4.56 % upon photoirradiation. During the grinding process, three different triboluminescent spectra were identified. Upon introduction of a mechanical stimulus, the triboluminescence emission is cyan, whereas after an extended period it changed to blue. After removing the mechanical stimulus, green-white phosphorescent emission was observed. Careful research on single-crystal structures and theoretical calculations demonstrate that strong Br⋅⋅⋅Br interactions are vital to facilitate spin-orbit coupling and promote intersystem crossing, thus generating the unique properties.