Novel up-conversion photoluminescent materials: noncoherent excitation by near-infrared sunlight

Our synthesized oligomer (OCACP) can convert the near-infrared (NIR) region of sunlight into visible light with assistance from ultraviolet (UV) light, and the mechanism includes UV quantum cutting and NIR two-photon absorption. Here, we report a high conversion rate (ΦF = 0.4108) for a wavelength-focusing photoluminescent OCACP with densely grafted 2-pyrazoline that was prepared by free-radical polymerization of 3-carbethoxy-5-acrylatecarbethoxy-2-pyrazoline, a chromophore with good fluorescence (ΦF = 0.0171). After polymerization, the densely grafted 2-pyrazoline significantly increased the interaction between the pyrazoline ring and formed a propeller shape, and the intramolecular pyrazoline ring rotations were physically restricted, which restrained the non-radiative pathway and accelerated the radiative pathway. These factors collectively contributed to the excellent fluorescence performance of OCACP. Additionally, OCACP achieved good-quality live-cell imaging with an enhancement in the fluorescence intensity through two-wavelength excitation of the cell rather than increasing the dye dosage or laser power and improved the visible portion of sunlight for more efficient use of solar energy.