1

Supporting Information

Singlet Fission from Upper Excited Electronic States

of Cofacial Perylene Dimer

Wenjun Ni a

, Gagik G. Gurzadyan*a, Jianzhang Zhao

a, Yuanyuan Che

a, Xiaoxin Li

a, Licheng

Sun*a,b

a State Key Laboratory of Fine Chemicals, Institute of Artificial Photosynthesis, Dalian

University of Technology, 116024 Dalian, , China

b Department of Chemistry, School of Engineering Sciences in Chemistry, Biotechnology and

Health, KTH Royal Institute of Technology, 10044 Stockholm, Sweden

Corresponding Authors

*Emails: gurzadyan@dlut.edu.cn (Gagik G. Gurzadyan), lichengs@kth.se (Licheng Sun)

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Experimental Section

Synthesis

Cofacial perylene dimer (Scheme S1) was synthesized by using cross-coupling reaction of 4,5-

dibromo-2,7-ditertbutyl-9,9-dimethylxanthene and 4,4,5,5-tetramethyl-2-(perylen-3-yl)-1,3,2-

dioxaborolane; these two precursors were synthesized as described in Refs. 1-4.

Scheme S1. Synthesis of perylene dimer. (a) tert-Butyl Chloride, FeCl3, DCM, r.t.,15h, yield:

61%; (b) Bromine, glacial acetic acid, 50 ℃, 20 h; yield: 51%; (c) NBS, DMF, r.t., 24 h; yield;

81%; (d) Pd (dppf) Cl2. CH2 Cl2 , 1,4-dioxane, CH3COOK,70 ℃, 17 h; yield: 65%; (e) Pd(PPh3)4,

K2CO3, 9:1 DMF: water, 110℃, 8h, yield: 37 %.

a: 9,9-dimethylxanthene (1) (1500 mg, 5.7 mM), tert-Butyl Chloride (1 ml,10 mM), CH2Cl2

(100 ml) and FeCl3 (100 mg, 0.6 mM) were added to 250 ml of three-necked flask, which

equipped with magnetic stirring and a drying tube. The reaction temperature was kept at room

temperature and continue to stir for 15 hours. The reaction mixture was extracted by H2O and

dried with MgSO4 over night and rotary evaporated to solid. The solid was suspended in ethanol

and recrystallized to get 1422 mg (61% yield) of 2,7-ditertbutyl-9,9-dimethylxanthene (2).

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b: 2,7-ditertbutyl-9,9-dimethylxanthene (2) (1400 mg, 4.3 mM) was first dissolved in glacial

acetic acid (20 ml) and bromine (1.4 ml, 15.6 mM) was added into solution during 10 minutes.

Reaction mixture was kept at 50℃ for 20 hours and then cooled down to room temperature,

water (50 ml) was added into the reaction flask. A K2CO3 solution was continuously added with

low speed until the mixture becomes pale green color. The mixture was extracted by CH2Cl2,

dried over MgSO4 and filtered to crude material. At last, the product was recrystallized with THF

and ethanol to afford white precipitate (1060 mg, 51% yield) of 4,5-dibromo-2,7-ditertbutyl-9,9-

dimethylxanthene.

c: N-bromosuccinimde (NBS) (1000 mg, 5.6 mM) was dissolved in DMF (50 ml) and was

added slowly into solution with perylene (1500 mg, 5.9 mM) (4) in N,N-dimethylformamide

(250 ml). Mixture was heated to 70℃ and kept stirring for 24 hours under nitrogen atmosphere.

When the mixture cooled down to room temperature, it was concentrated to crude material by

rotary evaporator. Finally, the solid was washed several times with water and dried in a vacuum

oven to get 3-bromoperylene (1590 mg, 81% yield) (5).

d: 3-bromoperylene (1590 mg, 4.818 mM) (5), CH3COOK (1370 mg, 14.402 mM), and

bis(pinacolato)diboron (3650 mg, 14.454 mM) were dissolved in 1,4-dioxane (200 ml) under

nitrogen. After full dissolution, 1,1’-bis(diphenylphosphino)ferrocene-palladium(II) dichloride

(Pd(dppf)Cl2. CH2Cl2) (200 mg, 0.279 mmol) was added into the stirring mixture and kept the

reaction at 70℃ for 17 hours. When the reaction system cooled down to room temperature, the

reaction solution was extracted with CH2Cl2 and then washed by saturated NaHCO3 solution and

brine. The product solution was dried by MgSO4 overnight and filtrated to obtain yellow powder.

Final product was purified by column chromatography on silica gel to get 4,4,5,5-tetramethyl-2-

(perylen-3-yl)-1,3,2-dioxaborolane (6) (1183 mg, 65% yield).

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e: 4,5-dibromo-2,7-ditertbutyl-9,9-dimethylxanthene (3) (499 mg, 1.0 mM), 4,4,5,5-

tetramethyl-2-(perylen-3-yl)-1,3,2-dioxaborolane (6) (1183 mg, 3.1 mM), K2CO3 (433 mg, 3.1

mM) and Pd(PPh3)4 (114 mg, 1.0 mM) were added to 100 ml of a 9;1 DMF: water mixture in a

250 ml round bottom flask. The mixture was heated at reflux for 8 hours under N2, cooled to

room temperature, and then 400 ml of distilled water was added to the flask. The product was

extracted with CH2Cl2 and solid product obtained upon drying under reduced pressure. The final

product was purified by column chromatography (petroleum ether / dichloromethane 9:1 v/v) to

deliver a yellow solid powder (317 mg, 37% yield). 1H NMR (400 MHz, CD2Cl2) 7.97 (d, J =

7.9 Hz, 1H), 7.87 (d, J = 8.2 Hz, 1H), 7.73 (d, J = 7.7 Hz, 1H), 7.68 – 7.63 (m, 3H), 7.55 – 7.47

(m, 4H), 7.39 (d, J = 7.8 Hz, 1H), 7.21 (dd, J = 14.3, 8.0 Hz, 5H), 7.16 – 7.04 (m, 5H), 6.99 (td, J

= 7.9, 4.3 Hz, 2H), 6.85 (ddd, J = 12.7, 9.3, 6.2 Hz, 3H), 1.92 (s, 3H), 1.76 (s, 3H), 1.34 (s, 18H).

HRMS (m/z) M+ = 822.3843 (calculated 822.3862);

Spectroscopic Measurements and Analysis

UV-vis absorption and fluorescence spectra were obtained by UV-Visible spectrophotometer

(Agilent, Cary 100) and spectrofluorometer (Horiba Jobin Yvon, Fluorolog-3), respectively.

Fluorescence lifetimes were measured by the time-correlated single photon counting (TCSPC)

technique (PicoQuant PicoHarp 300) at room temperature. By use of deconvolution/fit program

(PicoQuant FluFit) the time resolution was reached down to 10 ps. The instrument-response

function (IRF) of TCSPC techniques is given in Figure S1. The shorter fluorescence lifetimes

were recorded with a time resolved fluorescence spectrometer (Newport) in combination with a

mode-locked Ti-sapphire laser (Mai Tai DeepSee, Spectra-Physics). Briefly, the laser system

generated light pulses at 800 nm of duration 150 fs and a repetition rate 80 MHz. The emitted

fluorescence was focused into a BBO crystal together with the gate beam (800 nm) to create the

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up-converted signal at the sum-frequency generation (SFG). Overall time resolution of the setup

was 100 fs and laser excitation fluence was 1.2x10-6

J/cm2. Femtosecond transient absorption

spectra were measured by use of a home-made pump-probe setup, described in detail as

previously reported5. Briefly, it consists of a mode-locked Titanium-Sapphire amplified laser

system (Spitfire Ace, Spectra-Physics) which produces 35 fs pulses at 800 nm with 1 kHz

repetition rate and 4 W average power. Pump beam in the range of 240-2400 nm was generated

by use of Optical Parametric Amplifier (TOPAS, Light Conversion). Probe beam white light

continuum (WLC) was generated by focusing 10% of 800 nm laser pulse on a 3 mm thickness

rotated CaF2 plate, ranging between 350 and 850 nm. We arranged polarizations between pump

and probe beam magic angle (54.7°) in order to avoid rotational depolarization effects (except

for pump = 250 nm). Pump-probe measurements were performed under continuous movement of

the cuvette for homogeneous irradiation during exposure (concentration of 1.8x10-4

molL-1

). The

pump pulse duration was 30-40 fs (measured from the risetime of TA kinetics for rhodamine

6G). The average power of the excitation beam was 0.1 mW. The experimental data were fitted

to a multiexponential decay function convoluted with the instrument response function. Overall

time resolution was 20-30 fs.

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Figure S1. Instrument-response function and decay kinetics of fluorescence at ex =380 nm

measured by TCSPC technique.

All spectroscopic measurements (steady-state and time-resolved) were performed in 1 mm

fused silica cuvettes at absorbance A = 0.1-0.3 at the excitation wavelength.

Global lifetime analysis of time-resolved emission measurements were performed by Glotaran

software6. The Decay Associated Spectra (DAS) allow separating several overlapping emission

spectra, whereas Evolution Associated Spectra (EAS) analysis is more useful in sequential

kinetic model of TA data. Parallel model was used for global analysis of time-resolved

fluorescence.

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Quantum Yield of Fluorescence

Figure S2. Gaussian convolutions of the steady-state fluorescence spectra of perylene dimer in

hexane

𝑸 = 𝑸𝑹

𝑰

𝑰𝑹

𝑶𝑫𝑹

𝑶𝑫

𝒏𝟐

𝒏𝑹𝟐

where Q is the quantum yield, I is the integrated intensity, OD is the optical density, and n is the

refractive index. The subscript R refers to the reference fluorophore of known quantum yield7.

Here Rhodamine 6G was chosen as reference fluorophore (QR = 0.94 in ethanol).

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Time-Resolved Fluorescence Measurements

Table S1. Decay kinetics of fluorescence at various emission wavelengths (TCSPC data)

prob, nm 1, ns A1 2, ns A2

480 0.01 (fixed) 0.93 3.0 0.07

600 14 1

Figure S3. Fluorescence map of perylene dimer at ex = 400 nm by up-conversion technique

Table S2. Decay kinetics of fluorescence at various emission wavelengths (up-conversion data)

, nm 1, ps A1 2, ps A2 3, ps A3

480 1.28 0.59 19 0.31 1250 0.10

520 0.48 0.52 8.7 0.42 3000 0.06

560 1.33 0.50 13.8 0.38 3000 0.12

600 7.5 0.57 14000 0.43

620 12 0.36 14000 0.64

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Femtosecond Pump-Probe Measurements

Figure S4. Femtosecond transient absorption spectra of perylene monomer in hexane at 420 nm

excitation.

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Optimized Geometry

Figure S5. Optimized geometry of perylene dimer at the DFT calculation with Gaussian 09W

Table S3. Geometric Parameters Shown

1, o 2,

o 1 ,

o 2 ,

o 3,

o d1, Å d2, Å

74.18 74.14 -0.74 -0.76 0.00 4.20 4.53

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Global Fit of Time-Resolved Fluorescence Results

Figure S6. Global fit spectra of (a) TCSPC results and (b) up-conversion fluorescence results for

perylene dimer in hexane.

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Femtosecond Pump-Probe Measurements

Figure S7. Femtosecond transient absorption spectrum of perylene dimer in hexane at 335 nm

excitation.

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Singlet Fission Quantum yield

𝝓𝑺𝑭𝑿 = 𝝓𝑻

𝑺𝒕𝑶𝑫𝑻

𝑿

𝑶𝑫𝑻𝑺𝒕

𝜺𝑻𝑺𝒕

𝜺𝑻𝑿

whereOD is the maximum optical densities of triplet absorption and is the extinction

coefficients of the triplet absorption. The subscript St refers to the standard molecule of known

quantum yield and X refers to perylene dimer.8 Here benzophenone was chosen as standard

molecule (𝜙𝑇𝑆𝑡 = 1.0 in acetonitrile; 𝜀𝑇

𝑆𝑡 = 6500 M-1

cm-1

; 𝜀𝑇𝑋 = 14300 M

-1cm

-1 for perylene

monomer)9-10

. Perylene dimer and benzophenone were used under the same absorption at 250

nm.

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Difference Spectra

Figure S8. Difference spectra at the delay time of 5 ps were obtained when the normalized TA

spectrum at ex = 450 nm was subtracted by that at ex = 420 and 250 nm.

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