Supporting Information: Optical Spectroscopy

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1 Supporting Information: Optical Spectroscopy Aminofluorination of Cyclopropanes: A Multifold Approach through a Common, Catalytically Generated Intermediate Cody Ross Pitts, Bill Ling, Joshua A. Snyder, Arthur E. Bragg,* and Thomas Lectka* Contribution from the Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD Contents 1. Transient Absorption Spectroscopy Experimental Methods 2 Supplementary Figure S1. UV absorption spectra of PCP, NFSI and Selectfluor 2 Supplementary Figure S2. Determination of the S1 lifetime of PCP, PCP-d4, 4-fluoro-PCP and 4-tertbutyl-PCP by ns-tas. 3 Supplementary Figure S3. Comparison of PCP + absorption spectra obtained by various generation methods 4 Supplementary Figure S4. Broadband fs-tas of PCP excited at 266 nm 5 Supplementary Figure S5. Broadband µs-tas of PCP/Selectfluor excited at 266 nm 6 Supplementary Figure S6. fs-tas transients (700 nm) of photoexcited PCP in the presence and absence of Selectfluor 7 Supplementary Figure S7. Temporal characteristics of the µs-tas LED probe source 8 2. Fluorescence Spectroscopy Fluorescence Quantum Yield & Stern-Volmer Analysis Supplementary Figure S8. Fluorescence quantum yield determination for PCP 9 3. References 9 S1

2 1. Transient Absorption Spectroscopy 1.1. Experimental Methods Mixtures of 5 mm phenylcyclopropane (PCP)/50 mm Selectfluor and 20 mm PCP/20mM 3,3,4,4 -benzophenonetetracarboxylic dianhydride (BTDA) were prepared with purified acetonitrile (Solvent-Purification System PureSolv MD 5) and degassed with nitrogen. Samples were stirred continuously in 1 cm cuvettes for optical measurements. Measurements were also performed with mixtures of PCP/NFSI (5 mm/10 mm and 5 mm/50 mm in acetonitrile); these did not result in an observable absorption of the radical cation (PCP +), most likely due to the strong absorption of NFSI at 266 nm (Figure S1) that results predominately in direct excitation of NFSI rather than PCP. Additional control experiments were undertaken for 5 mm solutions of PCP (only) in acetonitrile to interrogate the excited-state kinetics of PCP. Our transient-absorption set-up has been described in detail elsewhere.1,2 Briefly, an amplified Ti:Sapphire laser (Coherent Legend Elite, 800 nm, 35 fs FWHM, 1 khz, 4.0 W) was frequency tripled to produce excitation pulses at 266 nm (10 mw). The excitation beam was focused at the sample to a 1 mm spot size. Three optical probe sources were used to interrogate kinetics on various timescales (fs, ns, µs): Femtosecond probe pulses were produced by using 800 nm to drive white-light generation in a 2 mm CaF2 plate (United Crystals); nanosecond pulses were generated with a pulsed 520 or 639 nm laser diode (Osram PL520, Opnext HL6358MG, ~2 ns FWHM) driven by a diode pulser (Highland Technologies T165); and microsecond pulses were generated with a white-light LED (Thorlabs LEDWE-15) driven by an electronic delay generator (Berkeley Nucleonics BNC 555, 500 ns FWHM, see Figure S6 for additional details). Femtosecond probe pulses were delayed by up to 50 ns by passing the probe continuum through ~ 5 meters of fiber optic cable. Figure S1 UV absorption spectra of PCP, NFSI and Selectfluor. S2

3 Figure S2. ns-tas of PCP and derivatives (no added quencher, probed by absorption at 639 nm) following photoexcitation with 266 nm. Transients were fitted with an exponential decay convoluted with the instrument response; PCP required an additional constant offset of 0.17 mod. Decay lifetimes are given in Table 2 of the main text. S3

4 Figure S3. Comparison of the PCP + absorption spectrum as probed Δt=50 ns following 266 nm photoexcitation of PCP/Selectfluor and 350 nm photoexcitation of PCP/BDTA; the latter has been translated vertically by 0.1 units for clarity. An absorption maximum at 540 nm is observed under both conditions; a broad underlying absorption obtained with the PCP/BDTA mixture is due to the generation of BDTA -, which absorbs at 710 nm. 3 S4

5 Figure S4. Broadband fs-tas of PCP in acetonitrile following 266 nm photoexcitation illustrates the evolution of S 1 PCP without Selectfluor. Spectra have been referenced to ΔOD of 0 at 600 nm to highlight the temporal evolution in spectral shape. S5

6 Figure S5 Broadband µs-tas of PCP/Selectfluor in ACN following photoexcitation with 266 nm. S6

7 Figure S6. Comparison of PCP S 1 kinetics as probed by fs-tas at 700 nm in the absence and presence of Selectfluor following 266-nm excitation. The trace of PCP (no quencher) was fit with a convoluted exponential decay with a constant offset (τ=318.7 ps, offset=0.8). The trace of the PCP/Selectfluor mixture was fit with a convoluted exponential decay (τ=869.2 ps); the decay constant is in close agreement with the S 1 lifetime predicted by the Stern-Volmer analysis for excited PCP in the presence of 50 mm Selectfluor (~ 0.8 ns). S7

8 Figure S2 Temporal profile of the µs-tas LED probe light source. The time-resolution of the LED is determined by the electronic response of the LED and the adjustable pulse-width of the delay/signal generator. Three representative pulse widths are shown above under filtered and unfiltered conditions. Comparisons of the filtered and unfiltered temporal profiles are shown to illustrate the slightly different responses of the primary diode emission (450 nm) and secondary emission generated by the phosphor blend ( nm). 2. Fluorescence Spectroscopy 2.1. Fluorescence Quantum Yield & Stern-Volmer Analysis Fluorescence quantum-yield determination and Stern-Volmer analysis of fluorescence quenching were carried out using a steady-state UV/vis (Stellarnet Black Comet) and fluorimeter (Perkin Elmer LS-5b); dispersed fluorescence was collected for excitation at 270 nm. Stock solutions of phenylcyclopropane and its analogs were prepared for both measurements. For Stern-Volmer experiments various quantities of Selectfluor were added to aliquots of stock solutions to maintain a constant optical density of ~0.1 at 270 nm (i.e. constant PCP concentration); all samples were degassed with nitrogen for 15 min. For determination of fluorescence quantum yields, solutions were diluted to various concentrations with their optical densities measured by UV/Vis absorption. Fluorescence spectra were integrated for analysis by linear least-squares regression. Stern-Volmer measurements were analyzed using Equation 1 of the main text; the fluorescence quantum yield of S8

9 phenylcyclopropane was determined to be 0.12 using Equation S1. 4 Φ!" =!!!!"#!!!"#!!!"#!"#!!!"# Φ!"!!"# (Eqn. S1) ΔI/ΔAbs slope of integrated emission as a function of absorbance n refractive index of solvent Figure S3 Fluorescence quantum yield (Φ fl ) of PCP determined with aerated Naphthalene as a reference References (1) Molloy, M. S.; Snyder, J. A.; Bragg, A. E. J. Phys. Chem. A. 2014, 118, (2) Snyder, J. A.; Bragg, A. E. J. Phys. Chem. A. 2015, 119, (3) Godbout, J. T.; Zuilhof, H.; Heim, G.; Gould, I. R.; Goodman, J. L.; Dinnocenzo, J. P.; Kelley, A. M. J. Raman Spectrosc. 2000, 31, 233. (4) Brouwer, A. M. Pure Appl. Chem. 2011, 83, (5) Hautala, R. R.; Schore, N. E.; Turro, N. J. J. Am. Chem. Soc. 1973, 95, S9