Measurement Details. UV-vis and Photoluminescence (PL) Spectroscopy. Optical measurements were performed on a UV-vis-NIR spectrometer (Agilent Technologies, Cary 5000) and a fluorescence spectrometer (PerkinElmer FL8500). All spectra were acquired under ambient conditions in a mixture of toluene and tetrahydrofuran (3:1) at room temperature (25 °C) in a cuvette of 1 cm pathlength. For thin-films, the solutions were dropcasted or spincoated on a thin glass coverslip.