Optically Activated Delayed Fluorescence Blake C. Fleischer, Jeffrey T. Petty, Jung-Cheng Hsiang, Robert M. Dickson, * School of Chemistry & Biochemistry and Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332-0400 and Department of Chemistry, Furman University, Greenville, SC Supplemental Information *Email: dickson@chemistry.gatech.edu Fluorescence spectra and lifetimes Fluorescence excitation and emission spectra were recorded on a fluorescence spectrophotometer Figure S1. Fluorescence excitation and emission spectra for 630 nm emitters. (Photon Technology International QM-4/2006), and are shown in Figure S1. The excitation peak matches the previously published absorption spectrum of this emitter, with a maximum near 560nm. 1 Fluorescence lifetimes under 560nm pulsed LED excitation were recorded on an Edinburgh Instruments Lifespec with an MCP PMT as a detector (Figure S2). A single 2.2ns lifetime is extracted from a reconvolution fit with the measured instrument response function. The IRF, lifetime data, and reconvolution fit are all plotted in Figure S2.
Figure S2. Time-correlated single photon counting-collected fluorescence lifetime of 630nm emitting Ag nanocluster in aqueous solution. Pulsed 560nm LED excitation at 5 MHz was used to excite emission. Emission was collected through a 20nm bandwidth filter centered at 630nm. Photon arrival times relative to the laser trigger are plotted in red. The instrument response function is the black curve (right y-axis), and the reconvolution fit is overplotted as the blue line on top of the red fluorescence data. A single exponential lifetime of 2.2ns is obtained from the fit.
Figure S3. Semi-log plot of Figure 1.
Figure S4. Excitation and emission spectra of SR101 used as background for data presented in Figure 6 of the manuscript. Excitation was at 560nm, collecting emission through a 590nm long pass and 694nm short pass filter. The quantum yield of SR101 is 0.9 and the peak extinction coefficient is 139,000 M -1 cm -1. 2
Mathematica Simulation Optimization Simulations were performed using initial photophysical parameters and experimental conditions derived from continuous wave enhancement studies. 1 Excitation using pulsed 532 nm primary excitation and either continuous wave (CW) or pulsed 803 nm secondary excitation were incorporated into the simulation. The rate matrix in equation 1 (main text) was exponentiated using either the pulsed-cw or pulsed-pulsed excitation conditions as indicated in the text. In each case, a fully populated ground state was used as the initial condition. Simulations were run varying both Φ "#$%& ' & and Φ "#$%( ' & (keeping them the equal to each other) while holding the σ %& and σ %( constant and different by a factor of 4 to reflect the 4-fold different measured slopes ( σ %& Φ "#$%& ' & and σ %( Φ "#$%( ' & ). S1 populations were used as surrogates of fluorescence, and decays outside the initial fluorescent lifetime were fit with biexponential decays. For each secondary-cw simulation, many different secondary powers were used with a given set of photophysical parameters, and fits of dark state decay vs secondary excitation intensity were compared to experimental values. Pulsed-pulsed excitations were also simulated using 1 ns pulse widths (the simulation time step) and 45 ns delays between primary and secondary pulses. For a given set of conditions, the ratio of primary- to secondary-induced fluorescence was compared to the dark state populations from the pulsed-cw secondary excitation intensity decays. Results from both were scaled proportionally to match experiment. Background Free Fluorescence Concentration Recovery Nanomolar solutions of Ag clusters and Sulforhodamine 101 (S101) dye were used to demonstrate concentration recovery using optically activated delayed fluorescence (OADF). A 10 MHz pulsed 560 nm diode laser (680 W/cm 2 ) was used for primary excitation and a CW 803-nm fiber-coupled diode laser (190 kw/cm 2 ) was used as secondary illumination. Emission was collected with an avalanche photodiode and time correlated single photon counting was performed with a Becker- Hickl SPC-630 card. Matlab (Mathworks, r2015a) was used to analyze the collected single photon counting data files and filter photons arriving in specific time windows after the primary pulse, allowing for time-gating to be executed in the analysis. (1) Hsiang, J. C.; Fleischer, B. C.; Dickson, R. M., Dark State-Modulated Fluorescence Correlation Spectroscopy for Quantitative Signal Recovery. J. Phys. Chem. Lett. 2016, 7, 2496-2501. (2) Birge, R. R., Kodak Laser Dyes. In Kodak Publication JJ-169, Eastman Kodak Company: Rochester, NY, 1987.