NMR. NMR data were acquired at ambient temperature. 500 MHz UV-Vis/NIR spectrophotometer. The fluorescence data and lifetimes were measured under nitrogen atmosphere using a Horiba Fluorolog-3 spectrofluorometer equipped with a 390 nm nanoLED and a FluoroHub R-928 detector. Absolute quantum yields (ΦF) were measured on the HORIBA Fluorolog-3 using a precalibrated Quanta-φ integrating sphere. Light from the sample compartment is directed into the sphere via a fiber-optic cable and an F-3000 Fiber-Optic Adapter, and then returned to the sample compartment (and to the emission monochromator) via a second fiber-optic cable and an F-3000 Fiber-Optic Adapter. Measurements at 77 K were performed by using a liquid nitrogen dewar assembly while purging the sample compartment with dry nitrogen. IR. Fourier transform infrared (FT-IR-ATR) spectra were obtained using a Thermo Fisher diffractometer equipped with a PhotonJet Cu-microfocus source (λ = 1.54184 Å) and a HyPix-6000HE detector. Data reduction was performed with CrysAlisPro 65, and subsequent data processing was also performed in CrysAlisPro (REF X1). Using the SCALE3 ABSPACK scaling algorithm, empirical absorption corrections were applied to the data for all four of the structures.