Decoding circular polarization with biaxially chiral fluorescence reporters

Chiroptical organic materials that interact asymmetrically with circularly polarized light will drive advancements in quantum cryptography, biosensing, and anti-counterfeiting. In this report, we show how biaxial chiral emitters can be used to decode the circular polarization of light. Specifically, we develop a library of contorted dithienophenazine chromophores that have a donor-acceptor-donor architecture, which we can straightforwardly access as both enantiomers (R/S). The tailored donor-acceptor interactions in this scaffold provide tunable absorption and emission across a broad range of wavelengths. These optical properties are retained in polymer-based films, which suggests that these molecular chromophores could be deployed in solid-state devices. Density functional theory reveals that installing increasingly electron-rich substituents to the dithienophenazine core significantly decreases the HOMO-LUMO gap. Chiral donor-acceptor-donor chromophores are sensitive to solvent polarity, protonation, and temperature, which provides access to emission across a >100 nm range. We find that the fluorescence intensity of these atropoisomeric chiral compounds depends on the circular polarization of the excitation source. This differential emission intensity can be increased by aggregation induced emission, which leads to fluorescence quantum yields exceeding 50%. Overall, we leverage this class of biaxially chiral chromophores to create a tunable library of fluorescent chiroptical materials that can be used to decode information stored in the spin angular momentum of photons.