Carotenoid Singlet Fission Reactions in Bacterial Light Harvesting. Complexes As Revealed by Triplet Excitation Profiles

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1 Polychromator Supporting Information Carotenoid Singlet Fission Reactions in Bacterial Light Harvesting Complexes As Revealed by Triplet Excitation Profiles Jie Yu, Li-Min Fu, Long-Jiang Yu,, Ying Shi, Peng Wang, Zheng-Yu Wang-Otomo, and Jian- Ping Zhang,* Department of Chemistry, Renmin University of China, Beijing 87, P. R. China Faculty of Science, Ibaraki University, Mito -85, Japan Department of Biology, Faculty of Science, Okayama University, Okayama 7-85, Japan S. Calibration of Near-Infrared Fluorescence Excitation Spectra In order to calibrate the near-infrared fluorescence excitation spectra (675 9 nm) measured by the FLS 98 spectrometer, we constructed an apparatus appended to this commercial spectrometer. As schematically shown in Figure S, the monochromatic excitation light from the built-in Xe lamp of FLS98 (45W) was directed to an integrating sphere (SM4, Edinburgh Instrument, UK), which was coupled to the entrance slit of a polychromator (MS54, SOL Instrument, Belarus). The multichannel CCD detection (DR-4B-FI-RES, ANDOR, UK) allowed an excitation spectrum and a fluorescence spectrum to be recorded simultaneously. The experimental procedures were described below. (i) A halogen calibrated light source (HL- -CAL, Ocean Optics, Germany) with known values of absolute intensity at various wavelengths ( 5 nm) was used to calibrate the spectral response of the appended system including the integrating sphere and the multichannel spectrometer. (ii) At a specific excitation wavelength, the fluorescence quantum yield of a LH-sample was obtained by dividing the fluorescence integral with the loss of the excitation light integral induced by sample absorption. (iii) A fluorescence excitation spectrum ( nm) measured with FLS 98 was calibrated based on the calibration curves determined in (i) and (ii). FLS 98 Integrating sphere CCD Figure S. Schematic illustration of the home-built setup for the calibration of the near-infrared fluorescence excitation spectra measure by the use of FLS 98. S

2 OD S. Linear Response Regime of Photoexcitation E Ex (mj) Figure S. Plot of the T n T absorption maxima of Car* at the delay time of t =.5 s against excitation energy (E Ex ) for the LHs from Tch. tepidum. Excitation and probing wavelengths were 5 nm and 565 nm, respectively. The rectangular shadow illustrates the regime of linear OD-E Ex dependence. An E Ex in this regime was used in the transient absorption measurements. The laser illumination spot size was.5 cm in diameter. Under this excitation condition, the fraction of photoexcited pigment molecules was estimated to be.~.%. S. Spectral Features of Steady-State Absorption and Resonance Raman Scattering TABLE S. The spectral features of steady-state absorption (Car, Qx, Qy, A Car /A Qy ) and carotenoid resonance Raman scattering (key Raman lines,,,, 4 ) of the LHs from Tch. tepidum and Rba. sphaeroides.4.. The Raman spectra were recorded under the excitation wavelength of 5 nm. Features Tch. tepidum Rba. sphaseroides.4. LH-RC LH LH-RC LH Car (-) 486 nm 47 nm 447 nm 45 nm (-) 54 nm 499 nm 47 nm 478 nm (-) 55 nm 5 nm 56 nm 5 nm Qx 59 nm 59 nm 59 nm 59 nm Qy B8 797/8 nm 8 nm B nm 849 nm LH Qy 95 nm 876 nm A Car /A Qy Raman shift (cm ) S

3 OD OD S4. Representative TA Spectra.5. (A) LH-RC-Tch 5 nm 95 nm () -. (B) LH-Tch 5 nm 87 nm () () (C) LH-RC-Rba - 5 nm () 875 nm () (D) LH-Rba nm 87 nm - () () () Figure S. Representative T n T transient absorption spectra of Car* at the delay time of.5 s recorded for the LHs from (A, B) Tch. tepidum and (C, D) Rba. sphaeroides.4.. Excitation wavelengths are shown as legends in each panel. TABLE S. Peak wavelengths of the transient absorption spectra of Car* for the LHs form Tch. tepidum and Rba. sphaeroides.4. (cf. Figure S). Transient Features Tch. tepidum Rba. sphaseroides.4. LH-RC LH LH-RC LH (T n T ) (-) 58 nm 565 nm 5 nm 5 nm (-) 55 nm 55 nm 49 nm 495 nm (S S ) (-) 5 nm 5 nm 47 nm 47 nm (-) 48 nm 465 nm 44 nm 445 nm S5. Calculation of -to- Ratios Under the Qy-excitation of low-energy BChls, e. g., B85, B875 and B95, the same Car* population ( n T TS ), originating solely from the TS mechanism, is responsible for both and of an OD spectrum. Based on Beer-Lambert s law, the -to- ratio can be written as R TS = OD TS T (Qy) OD TS G (Qy) = n TS T ε T = εt n T TSε G ε G (S) where ε T and ε G represent the extinction coefficients of the T n T and the S S absorption of Car, respectively. S

4 OD T (A) LH-RC-Tch = 58 nm OD T (B) LH-Tch = 565 nm OD T (C) LH-RC-Rba = 5 nm OD T (D) LH-Rba = 5 nm Figure S4. The neat contribution to the Car* absorption and the corresponding bleaching of the ground state absorption for the LHs from (A, B) Tch.tepidum and (C, D) Rba. sphaeroides.4.. Shaded area indicate the carotenoid excitation regions for calculating R. Under the Car-excitation, the and contributed via reactions, denoted as OD T (Car) and OD G (Car) respectively, can be obtained following the protocols for deriving the -yielded Car* as described in the main text. (The results thus obtained are depicted in Figure S4.) In this case, the -resultant -to- ratio can be written as R = OD T (Car) OD = n T ε T G (Car) m G ε G (S) where the Car* population responsible for, n T, may differ from that for, m G, depending on the intermolecular or intramolecular schemes. Comparing Eq. S and Eq. S, we have R = n T R TS m G. In the case of intermolecular scheme ( m G scheme ( m G = n T ), we should observe R = R TS. Otherwise for the intramolecular = n T /), we should see R = R TS. Thus the R /R TS value allows us to experimentally derive the S4

5 reaction scheme without invoking the extinction coefficients ε T and ε G. (A) LH-RC-Tch = 58 nm (B) LH-Tch = 565 nm TPE TPE TEP - TEP (C) LH-RC-Rba = 5 nm (D) LH-Rba = 5 nm TPE TPE TEP - TEP Figure S5. The overall TEPs for the LHs from (A, B) Tch.tepidum and (C, D) Rba. sphaeroides.4.. Shaded area indicate the Qy-excitation regions of low-energy BChls for calculating R TS. As shown by the shadow area in Figure S4, we derived the R = OD T (Car)/ OD G (Car) values based on the neat contributed and under the Car excitation. On the other hand, as indicated by the shadow area in Figure S5, we obtained the R TS = OD T TS (Qy)/ OD G TS (Qy) values based on the overall TEPs under the Qy-excitation of low-energy BChls. S5