Electronic Supplementary Information

Spectroscopic study of the excited state proton transfer processes of (8-bromo-7-hydroxyquinolin-2-yl)methyl-protected phenol in

aqueous solutions

Jinqing Huang,a,‡ Adna Muliawan,b,‡ Jiani Ma,*c Ming De Li,a Hoi Kei Chiu,a Xin Lan,a Davide Deodato,b David Lee Phillips,*,a and Timothy M. Dore*,b,d

a Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong,

People’s Republic of China b New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, United Arab Emirates

c Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an, People’s

Republic of China. d Department of Chemistry, University of Georgia, Athens, GA 30602, USA

‡ These authors contributed equally to this work. Figure S1. UV-Vis absorption spectrum of BHQ-OPh in acetonitrile ...................................... 3 Figure S2. UV-Vis absorption spectra of BHQ-OPh in acetonitrile and

1:1 acetonitrile/PBS (pH 7.4). ........................................................................... 3 Figure S3. Titration of BHQ-OPh and BHQ-OAc to determine pKa of the phenolic proton ..... 3 Figure S4. Simulated absorption spectrum of BHQ-OPh (N) ................................................. 4 Figure S5. Simulated absorption spectrum of BHQ-OPh (A) ................................................. 4 Figure S6. Frontier molecular orbitals of the strongest oscillator strength transition

at 227.78 nm for BHQ-OPh (N) ........................................................................ 5 Figure S7. Comparison between low power 266-nm resonance Raman spectrum

of BHQ-OPh in 1:1 acetonitrile/water and the DFT calculated Raman spectra of the S0 state of BHQ-OPh (N) and BHQ-OPh (A) ............................. 5

Figure S8. Comparison between low power 240-nm resonance Raman spectrum of BHQ-OPh in 1:1 acetonitrile/water (pH 5) solution and the DFT calculated Raman spectrum of the S0 state of BHQ-OPh (N) ........................................... 6

Figure S9. Simulated absorption spectrum for the T1 state of BHQ-OPh (N) ......................... 6 Figure S10. Simulated absorption spectrum for the T1 state of BHQ-OPh (A) ....................... 6 Figure S11. ns-TA spectra of BHQ-OPh in PBS (pH 7.4) after 266-nm excitation .................. 7 Figure S12. Fit of the ns-TA spectra in Fig. 4c to determine the rate constant for the

decay of the T1 state of BHQ-OPh (T) .............................................................. 7 Figure S13. Comparison between high power 240-nm resonance Raman spectrum

of BHQ-OPh in acetonitrile and the DFT calculated Raman spectra of the T1 and S0 states of BHQ-OPh (N) .......................................................... 7

Electronic Supplementary Material (ESI) for Photochemical & Photobiological Sciences.This journal is © The Royal Society of Chemistry and Owner Societies 2017

2

Figure S14. ns-EM spectra of BHQ-OPh in PBS (pH 7.4) after 266-nm excitation ................ 8 Figure S15. fs-TA spectra of BHQ-OPh in 1:1 acetonitrile/PBS (pH 7.4) after 266-nm

excitation .......................................................................................................... 9 Figure S16. Comparison between the high power 240-nm resonance Raman

spectrum of BHQ-OPh in 1:1 acetonitrile/PBS (pH 7.4) and the DFT calculated Raman spectra of the T1 and S0 states of BHQ-OPh (A) .............. 10

Figure S17. fs-TA spectra of BHQ-OPh in 1:1 acetonitrile/water (pH 5.0) after 266-nm excitation ........................................................................................................ 10

Scheme S1. Proposed mechanism of BHQ-OPh photoprocesses in acetonitrile ................. 11 Table S1. Selected electronic transition energies, oscillator strength, and molecular

orbital transitions from TD-DFT calculations .................................................. 11

3

Figure S1. UV-Vis absorption spectrum of BHQ-OPh in acetonitrile.

Figure S2. UV-Vis absorption spectra of BHQ-OPh in acetonitrile and 1:1 acetonitrile/PBS (pH 7.4).

Figure S3. Titration of BHQ-OPh (left) and BHQ-OAc (right) to determine the pKa of the phenolic proton. BHQ-OPh or BHQ-OAc was dissolved in buffers of known pH, and its spectral maxima were noted by UV-vis at 331 (phenol) and 371 nm (phenolate) (or 330 and 368 nm for BHQ-OAc). The ratio of the absorbance at the two reference wavelengths was plotted vs pH of the buffer. The plot is fitted with a sigmoidal regression and the pKa was calculated by solving for the inflection point. Buffers (pH): phosphate (3.91, 6.73, 7.32, and 7.86), acetate (5.13 and 5.65), citrate (6.17), borate (8.59 and 9.47).

200 300 400 500 600

Ab

sorb

ance

Wavelength (nm)

CH3CN

200 300 400 500 600

Abso

rban

ce

Wavelength (nm)

CH3CN pH=7.4 CH3CN/PBS (1/1)

4

Figure S4. Simulated absorption spectrum of BHQ-OPh (N) obtained from TD-DFT calculation at the level of B3LYP/6-311G**.

Figure S5. Simulated absorption spectrum of BHQ-OPh (A) obtained from TD-DFT calculation at the level of B3LYP/6-311G**

5

Figure S6. Frontier molecular orbitals of the strongest oscillator strength transition at 227.78 nm for BHQ-OPh (N).

Figure S7. Comparison between low power 266-nm resonance Raman spectrum of BHQ-OPh in 1:1 acetonitrile/water and the DFT calculated Raman spectra of N(S0) and A(S0) of BHQ-OPh.

266nm probeLow Power

800 1000 1200 1400 1600 1800Raman Shift (cm-1)

A(S0)

N(S0)

**CH3CN/H2O

Rel

ativ

e In

tens

ity (a

.u.)

85(LUMO+1)

84(LUMO)

83(HOMO)

82(HOMO-1)

81(HOMO-2)

0.48

0.10

6

Figure S8. Comparison between low power 240-nm resonance Raman spectrum of BHQ-OPh in 1:1 acetonitrile/water (pH 5) solution and the DFT calculated Raman spectrum of N(S0) of BHQ-OPh.

Figure S9. Simulated absorption spectrum for the T1 state of BHQ-OPh (N) obtained from TD-DFT calculation at the level of B3LYP/6-311G**

Figure S10. Simulated absorption spectrum for the T1 state of BHQ-OPh (A) obtained from TD-DFT calculation at the level of B3LYP/6-311G**

800 1000 1200 1400 1600 1800

NBr

HO OPh

N(S0) of BHQ-OPh

R

elat

ive

Inte

nsity

(a.u

.)

Raman Shift (cm-1)

N(S0)

240 nm probe low power pH=5

7

Figure S11. ns-TA spectra of BHQ-OPh in PBS (pH 7.4) after 266-nm excitation.

Figure S12. Fit of the ns-TA spectra in Fig. 4c to determine the rate constant for the decay of the T1 state of BHQ-OPh (T).

Figure S13. Comparison between high power 240-nm resonance Raman spectrum of BHQ-OPh in acetonitrile and the DFT calculated Raman spectra of the T1 and S0 states of BHQ-OPh (N).

300 400 500 600 700Wavelength (nm)

DOD

0 ns 100 ns 300 ns 600 ns

410

528

328

0 500 1000 1500 2000 2500

DO

D

Time (ns)

l=380 nm

800 1000 1200 1400 1600 1800

acetonitrile

N(S0)

Raman Shift (cm-1)

Rel

ativ

e In

tens

ity (a

.u.)

*

High PowerBHQ-OPh

N(T1)

Curve fit: 𝑦 = 𝑦# + 𝐴&𝑒((*(*+)/./

y0=0.007030x0=51.73233A1=0.056530t1=874.97694

8

Figure S14. ns-EM spectra of BHQ-OPh in PBS (pH 7.4) after 266-nm excitation.

300 400 500 600

450R

elat

ive

Inte

nsity

(a. u

.)

Wavelength (nm)

0 ns 10 ns 20 ns 30 ns 50 ns

9

(a) (b)

(c)

Figure S15. fs-TA spectra of BHQ-OPh in 1:1 acetonitrile/PBS (pH 7.4) after 266-nm excitation. (a) The growth of the 355-nm absorption band within 1 ps results from excitation from the ground state BHQ-OPh (A). (b) Subsequently, there is a conversion with an emission band at 450 nm and an absorption band at 635 nm. Based on the assignments for the ns-EM spectra in 1:1 acetonitrile/PBS (pH 7.4) (Fig. 7), the emission band at 450 nm is attributed to the fluorescence from the S1 state of BHQ-OPh (A). Hence, the conversion in (b) can be assigned to the formation of the S1 state of BHQ-OPh (A). (c) The growing features at 410 and 528 nm are assigned to the T1 state of BHQ-OPh (A) based on the ns-TA spectra (Fig. 4). The conversion in (c) indicates the intersystem crossing from the S1 state of BHQ-OPh (A) to the T1 state of BHQ-OPh (A).

400 500 600 700

410

DOD

Wavelength (nm)

0.1 ps 0.4 ps 0.5 ps

355

400 500 600 700

410

0.6 ps 0.7 ps 0.9 ps 1.2 ps 2.0 ps 8.0 ps

DOD

Wavelength (nm)

450

635

400 500 600 700

180.0 ps 330.0 ps 780.0 ps 1530.0 ps 2330.0 ps 3030.0 ps

DOD

Wavelength (nm)

528

450 635

410

10

Figure S16. Comparison between the high power 240-nm resonance Raman spectrum of BHQ-OPh in 1:1 acetonitrile/PBS (pH 7.4) and the DFT calculated Raman spectra of the T1 and S0 states of BHQ-OPh (A).

Figure S17. fs-TA spectra of BHQ-OPh in 1:1 acetonitrile/water (pH 5.0) after 266-nm excitation.

800 1000 1200 1400 1600 1800Raman Shift (cm-1)

240 nm high power ACN:PBS=1:1

A(T1)

A(S0)

NBr

O OPh

A(S0) of BHQ-OPh

400 500 600 700

0.0 ps 0.1 ps 0.2 ps 0.3 ps 0.4 ps 0.6 ps 0.9 ps

DOD

Wavelength (nm)

359

400 500 600 700

0.9 ps 1.4 ps 2.8 ps 13.3 ps

DOD

Wavelength (nm)

390

*

359

452

630

400 500 600 700

44.0 ps 530.0 ps 1330.0 ps 2530.0 ps

DOD

Wavelength (nm)

370*

480

630

11

Scheme S1. Proposed mechanism of BHQ-OPh photoprocesses in acetonitrile. Table S1. Selected electronic transition energies, oscillator strength in the region of 210-310 nm, and molecular orbital transitions for the strongest oscillator strength transition at 227.78 nm obtained from (U)B3LYP/6−311G** TD−DFT calculations for the neutral form of BHQ-OPh.

NHOBr

OPh

S0 of BHQ-OPh (N)

hνCH3CN

S1 of BHQ-OPh (N) ISC T1 of BHQ-OPh (N)

fluorescence

S0 of BHQ-OPh (N)

decay

S0 of BHQ-OPh (N)

NHOBr

OH HOPh

BHQ-OH

X

NeutralForm

ExcitationEnergy(nm) OscillatorStrength

MolecularOrbitalTransitionsfor227.78excitation

211.42 0.0099

216.88 0.0002 78 -> 84 -0.25951

217.12 0.0043 78 -> 85 -0.12958

222.38 0.1865 81 -> 84 -0.27312

227.78 0.6085 81 -> 85 0.10130

228.02 0.0001 81 -> 88 -0.11514

236.93 0.0227 82 -> 85 0.47862

244.56 0.0002 83 -> 85 -0.20895

245.78 0.0262

258.94 0.0031

281.48 0.0549

283.71 0.0013