Supporting Information for: Getting to the (Square) Root of the Problem: How to Make Non-Coherent Pumped Upconversion Linear

Transcription

1 Supporting Information for: Getting to the (Square) Root of the Problem: How to Make Non-Coherent Pumped Upconversion Linear Alexandre Haefele, Jörg Blumhoff, Rony S. Khnayzer, and Felix N. Castellano* Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio S1

2 Materials PdOEP and DPA were obtained from Frontier Scientific and Aldrich Chemical Company, respectively, and used without further purification. Spectroscopic grade toluene was obtained from Aldrich. Spectroscopic Measurements Static absorption spectra were measured with a Cary 50 Bio UV-Vis spectrophotometer from Varian. Steady-state luminescence spectra were obtained on a FL/FS920 from Edinburgh Instruments or with a PTI Instruments spectrofluorimeter, achieving excitation with a 450 W or a 75 W Xe arc lamp, respectively. Excitation power was measured using a Nova II/PD300-UV power meter/detector head from Ophir. In experiments utilizing monochromatic laser excitation, the nm line from an Ar + laser (Coherent, Innova 300) was isolated using a bandpass filter. In all experiments, different excitation powers were realized by using a series of neutral density filters. Single wavelength emission intensity decays were acquired with a N 2 pumped dye laser (2-3 nm fwhm) from PTI (GL-3300 N 2 laser, GL-301 dye laser). Coumarin 500 was used to tune the unfocused pulsed excitation beam to selectively excite PdOEP. All luminescence samples were prepared either in 1 cm 2 anaerobic quartz cells purchased from Starna Cells or in a specially designed 1 cm 2 optical cell bearing a side arm round bottom flask and were either deoxygenated for at least 30 minutes with high purity argon or subjected to a minimum of three freeze-pumpthaw cycles (8-10 µ vacuum) prior to all measurements. Stern-Volmer Quenching The Stern-Volmer (K SV ) and the bimolecular quenching constants (k q ) were obtained according to the dynamic Stern-Volmer relation, τ 0 /τ = 1 + K SV [Q], where τ 0 and τ are the PdOEP lifetimes in the absence or presence of the quencher, respectively. K SV is the Stern-Volmer constant, K SV = k q τ 0, and [Q] is the molar concentration of DPA. The Stern-Volmer slope was linear over the entire range of quencher concentrations. S2

3 Figure S1. Absorption spectra of the samples used for the Stern-Volmer measurements in toluene. Figure S2. Luminescence intensity decay profiles of PdOEP measured as a function of DPA concentration in deareated toluene (C500 laser dye, emission detected at 665 nm). S3

4 Figure S3. Stern-Volmer plot generated from lifetime quenching of PdOEP with DPA in deareated toluene, using the single exponential fits to the data set from Figure S2. S4

5 Power Dependence with Coherent Photons For this experiment, a bandpass filter (514.5 nm) was used to filter the excitation beam and upconversion intensities at 420 ± 6 nm were recorded over one minute in time-based mode and averaged. For higher excitation powers, the use of neutral density filters prior to the detector was necessary to prevent PMT saturation. The final emission intensities in the latter samples were corrected for the filter transmittance at 420 nm. Figure S4. Absorption spectrum of the PdOEP/DPA sample used for the power dependence measurements with laser excitation. The inset represents a zoom-in of the area of excitation (λ exc = nm) centered on the first Q-band. S5

6 Figure S5. Normalized upconversion intensities at 420 nm plotted as a function of the incident laser power density in the weak annihilation region, mw/cm 2. The inserted function on the graph, y = x 2 (blue), indicates the incident quadratic dependence in the low power regime of this experiment. This is the same data as presented in Figure 2. Figure S6. Normalized upconversion intensities at 420 nm plotted as a function of the incident laser power density in the strong annihilation region, W/cm 2. The inserted function on the graph, y = x (black), indicates linear dependence in the high power regime. This is the same data as presented in Figure 2. S6

7 Power Dependence with Non-Coherent Photons Figure S7. Absorption spectrum of the PdOEP/DPA sample used for power dependence measurements with non-coherent excitation. The inset represents a zoom-in of the Q-band region indicating the 3 wavelengths of excitation in Figure 3 (λ ex = 515, 530 and 545 nm). Figure S8. Example of the upconverted emission intensity profile of DPA in toluene following selective excitation of PdOEP (λ ex = 545 nm/455 nm long pass filter, O.D. = 0.29) measured as a function of incident light power density. Upconversion initiates under these experimental conditions at a power density of 140 µw/cm 2. S7

8 Figure S9. Sun (AM 1.5) irradiance as a function of wavelength as obtained from NREL. 1 The integrated irradiance supplied by the sun across the absorption spectrum of the PdOEP sensitizer ( nm, green area) is 13 mw cm -2. Figure S10. Photon flux from the sun (AM 1.5) as a function of wavelength as calculated from Figure S9. The integrated photon flux supplied by the sun across the absorption spectrum of the PdOEP sensitizer ( nm, green area) is ~ photons cm -2 s -1. Reference 1 National Renewable Energy Laboratory (NREL), MS Excel TM spreadsheet file downloaded from < S8