Poly ethylene glycol standards

NMR spectra were recorded on a Bruker-600 MHz spectrometer. Chemical shifts for ¹H NMR spectra were reported in parts per million relative to a singlet at 7.26 ppm for the residual chloroform in deuterated chloroform. Chemical shifts for ¹³C NMR were reported relative to the centerline of a triplet at 77.16 ppm for deuterated chloroform. Molecular weights and polydispersity indices were determined by GPC in THF (20 °C; flow rate 1 mL min^–1) using Polymer Labs 5 μm mixed-C columns, a Hewlett-Packard 1100 instrument equipped with a laser refractometer LR40 (Viscotek), and Viscotek software (TriSEC GPC Version 3.0, Viscotek Corp.). Poly(ethylene glycol) standards (Polymer Laboratories) were used for molecular weight calibration. Samples were dissolved in THF (0.4% w/v) and passed through a 0.2 μm filter before injection. Steady-state fluorescence emission spectra were recorded on a Horiba FluoroMax-4 spectrofluorometer. High-resolution mass spectra were obtained from the University of Illinois at Urbana-Champaign (UIUC) Mass Spectrometry Facility. UV-Vis spectra were produced from a Hewlett-Packard 8452A diode-array spectrophotometer. Unless otherwise noted, materials were obtained from commercial suppliers and were used without further purification. All of the solvents were either HPLC or spectroscopic grade in the optical spectroscopic studies.