Homogeneous solar fuels photocatalytic systems often require several additives in solution with the catalyst to operate, such as a photosensitizer (PS), Brønsted acid/base, and a sacrificial electron donor (SED). Tertiary amines, in particular triethylamine (TEA) and triethanolamine (TEOA), are ubiquitously deployed in photocatalysis applications as SEDs and are capable of reductively quenching the PS’s excited state. Upon oxidation, TEA and TEOA form TEA•+ and TEOA•+ radical cations, respectively, which decay by proton transfer to generate redox non-innocent transient radicals, TEA• and TEOA•, respectively, with redox potentials that allow them to participate in an additional electron transfer step, thus resulting in net one-photon/two-electron donation. However, the properties of the TEA• and TEOA• radicals are not well understood, including their reducing powers and kinetics of electron transfer to catalysts. Herein, we have used both pulse radiolysis and laser flash photolysis to generate TEA• and TEOA• radicals in CH3CN, and combined with UV/Vis transient absorption and time-resolved mid-infrared spectroscopies, we have probed the kinetics of reduction of the well-established CO2 reduction photocatalyst, fac-ReCl(bpy)(CO)3 (bpy = 2,2′-bipyridine), by these radicals [kTEA• = (4.4 ± 0.3) × 109 M−1 s−1 and kTEOA• = (9.3 ± 0.6) × 107 M−1 s−1]. The ∼50× smaller rate constant for TEOA• indicates, that in contrast to a previous assumption, TEA• is a more potent reductant than TEOA• (by ∼0.2 V, as estimated using the Marcus cross relation). This knowledge will aid in the design of photocatalytic systems involving SEDs. We also show that TEA can be a useful radiolytic solvent radical scavenger for pulse radiolysis experiments in CH3CN, effectively converting unwanted oxidizing radicals into useful reducing equivalents in the form of TEA• radicals.

Bright biocompatible fluorescent imaging dyes with red to near-infrared (NIR) emissions are ideal candidates for fluorescence microscopy applications. Pyrene–benzothiazolium hemicyanine dyes are a new class of lysosome-specific probes reported on recently. In this work, we conduct a detailed implementation study for a pyrene–benzothiazolium derivative, BTP, to explore its potential imaging applications in fluorescence microscopy. The optical properties of BTP are studied in intracellular environments through advanced fluorescence microscopy techniques, with BTP exhibiting a noticeable shift toward blue (λ_em ≈ 590 nm) emissions in cellular lysosomes. The averaged photon arrival time (AAT)-based studies exhibit two different emissive populations of photons, indicating the probe’s dynamic equilibrium between two distinctively different lysosomal microenvironments. Here, BTP is successfully utilized for time-lapse fluorescence microscopy imaging in real-time as a ‘wash-free’ imaging dye with no observed background interference. BTP exhibits an excellent ability to highlight microorganisms (i.e., bacteria) such as Bacillus megaterium through fluorescence microscopy. BTP is found to be a promising candidate for two-photon fluorescence microscopy imaging. The two-photon excitability of BTP in COS-7 cells is studied, with the probe exhibiting an excitation maximum at λ_TP ≈ 905 nm.

Spin chemistry of photogenerated spin-correlated radical pairs (SCRPs) offers a practical approach to control chemical reactions and molecular emissions using weak magnetic fields. This capability to harness magnetic field effects (MFEs) paves the way for developing SCRPs-based molecular qubits. Here, we introduce a new series of donor-chiral bridge-acceptor (D-χ-A) molecules that demonstrate significant MFEs on fluorescence intensity and lifetime in solution at room temperature – critical for quantum sensing. By precisely tuning the donor site through torsional locking, distance extension, and planarization, we achieved remarkable control over key quantum properties, including field-response range and linewidth. In the most responsive systems, emission lifetimes increased by over 200%, and total emission intensity was modulated by up to 30%. This level of tunability, and rational design principle of optically addressable molecular qubits, represents a major leap toward functional synthetic molecular qubits, advancing the field of molecular quantum technologies.