The spectral modification of sunlight from less efficient green (500–600 nm) to more efficient red (600–700 nm) by light-converting fluorescent dyes has been widely studied for enhancing the microalgal biomass productivity. In particular, deep-red (650–700 nm) photons, which are mainly used by photosynthetic pigments of microalgae for photosynthesis, play a key role in promoting microalgal growth. In this study, we have synthesized three different deep-red emitting diketopyrrolopyrrole (DPP) dyes and utilized two of them to fabricate light-converting films for microalgal cultivation. The introduction of free-rotatable triphenylamine (TPA) moieties into DPP dyes enabled them to exhibit excellent solid state emission via aggregation-induced emission (AIE). As a result, cultured microalgae showed different biomass and lipid productivity according to the degree of increase in the photosynthetic photon flux density (PPFD) of the light-converting films. In detail, strong deep-red emission of the light-converting film prepared using dye E2 increased the total fatty acid methyl ester (FAME) content of microalgae up to 62.4%. In contrast, the weak deep-red emission of the light-converting film based on dye M2 resulted in an enhancement of only 28.8%. These results show that the deep-red emitting AIE-DPPs could potentially be applied in light-converting film materials for accelerating the mass production of microalgae.

Conventional fluorescent dyes have the property of decreasing fluorescence due to aggregation-caused quenching effects at high concentrations, whereas aggregation-induced emission dyes have the property of increasing fluorescence as they aggregate with each other. In this study, diketopyrrolopyrrole-based long-wavelength aggregation-induced emission dyes were used to prepare biocompatible nanoparticles suitable for bioimaging. Aggregation-induced emission nanoparticles with the best morphology and photoluminescence intensity were obtained through a fast, simple preparation method using an ultrasonicator. The optimally prepared nanoparticles from 3,6-bis(4-((E)-4-(bis(40-(1,2,2-triphenylvinyl)-[1,10-biphenyl]-4-yl)amino)styryl)phenyl)-2,5-dihexyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DP-R2) with two functional groups having aggregation-induced emission properties and additional donating groups at the end of the triphenylamine groups were considered to have the greatest potential as a fluorescent probe for bioimaging. Furthermore, it was found that the tendency for aggregation-induced emission, which was apparent for the dye itself, became much more marked after the dyes were incorporated within nanoparticles. While the photoluminescence intensities of the dyes were observed to decrease rapidly over time, the prepared nanoparticles encapsulated within the biocompatible polymers maintained their initial optical properties very well. Lastly, when the cell viability test was conducted, excellent biocompatibility was demonstrated for each of the prepared nanoparticles.

The development of highly stable organic small molecules for optical applications is of growing interest. Multimerization of monomeric small molecules can enhance stability via increased π–π stacking, but it often reduces solubility and induces undesirable spectral shifts due to π‐extension. To overcome this trade‐off, we report a trimeric small molecule (F‐TPBT) derived from a model monomer (Tinuvin 327) using a 1,3,5‐fluorinated phenyl linker. This design markedly improves thermal stability and solubility while minimizing changes in the optical absorption spectrum. F‐TPBT shows superior thermal properties (5 wt% decomposition temperature = 427 °C; weight loss after 1 hour at 300 °C = 0.32 wt%) and excellent solubility (5.3 wt% in dichloromethane; 6.4 wt% in N‐methylpyrrolidone (NMP)), with an absorption spectrum nearly identical to that of Tinuvin 327. These properties make F‐TPBT a promising UV light absorber for transparent polyimide (TPI) films, which require processing above 300 °C and are widely used in flexible displays. Notably, F‐TPBT‐containing films retain their absorption properties even after 80 hours of accelerated UV irradiation, demonstrating excellent photostability. This study presents a broadly applicable molecular design strategy for enhancing the stability and solubility of organic small molecules while avoiding significant spectral shifts.