Polymerizable aggregation-induced emission enhancement (AEE) dyes with D-A-D’ structure basing on phenothiazine and tetraphenylethylene for fluorescent particles and their application in cell imaging

Organic fluorescence dyes with long wavelength emission are attracting people’s interests in bioimaging, cells tracing and medical diagnosis due to their many advantages. This contribution exhibited a novel red fluorescent monomer BDPPA with traditional tetraphenylethylene (TPE) and phenothiazine (PHT) as structural units, which showed aggregation-induced emission enhancement (AEE) effects together with the twisted intramolecular charges transfer (TICT) owing to its D-A-D’ structure. The maximal emission wavelength of BDPPA located at 592 nm with a shoulder peak at 629 nm. Afterwards, the amphiphilic PEG-BD copolymers was acquired by RAFT polymerization of BDPPA and PEGMA. When the feeding ratio of BDPPA increased from 10.0 % to 20.0 %, the ratio of BDPPA in PEG-BD copolymers correspondingly increased from 9.6 % to 20.9 %. The obtained amphiphilic PEG-BD could self-assemble into fluorescence organic nanoparticles (FONs) with about 150 nm diameter in H 2 O solution. Owing to their TICT effect and D-A-D’ structure, both BDPPA and PEG-BD copolymers showed obvious fluorescence in THF solvent, and their intensity firstly decreased and then grew with the increase of water concentration, indicative of the obvious aggregation-induced emission enhancement (AEE). From the calculations of energy quantum, the difference ΔE of BDPPA decreased to 3.09 eV from 3.53 eV of its substrate PHT, which was very favourable for the long wavelength emission and cell imaging. Moreover, due to the long wavelength emission, excellent water solubility and biocompatibility, and AEE effect, the obtained PEG-BD FONs revealed the promising application in biological imaging field.