Supporting Information
Optically Triggered Stepwise Double Proton Transfer in an
Intramolecular Proton Relay: A Case Study of
1,8-Dihydroxy-2-naphthaldehyde (DHNA)
Chia-Yu Peng,¶,† Jiun-Yi Shen,¶, ‡ Yi-Ting Chen,‡ Pei-Jhen Wu,‡ Wen-Yi Hung,§ Wei-Ping Hu,†,* and
Pi-Tai Chou‡,*
†
Department of Chemistry and Biochemistry, National Chung Cheng University, Chia-Yi 62102,
Taiwan, R.O.C.
‡
Department of Chemistry and Center for Emerging Material and Advanced Devices, National Taiwan
University, Taipei 10617, Taiwan, R.O.C.
§
Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung 20224, Taiwan,
R.O.C.
¶
These authors contributed equally to this work.
Corresponding Author
Email:[email protected] (P.-T. Chou)
Email: [email protected] (W.-P. Hu)
S1
Contents
page
Figure S1. Side views of the packing of DHNA in the unit cell...........................................................S4
Figure S2. The 1H NMR spectroscopy of DHNA and HN12............................................................... S5
Figure S3. Normalized steady-state absorption spectrum (black lines) and excitation spectra (monitor
at 520 nm (red) and 650 nm (blue)) for DHNA in cyclohexane at room temperature.......................... S6
Figure S4 Time-resolved femtosecond fluorescence upconversion of DHNA in cyclohexane
monitored at 450 nm (black open square, □, an average of five replicas) and instrument response
function (red). ....................................................................................................................................... S6
Figure S5. Time-resolved relaxation dynamics of DHNA in solid state monitored at 520 nm (black
open circles, ○), and 650 nm, (blue open square,□). Solid lines depict the corresponding fitting
curves (black and blue) and instrument response function (red)........................................................... S7
Figure S6. Calculated relative energies (kcal/mol) and wavelengths (nm) of vertical excitation and
emission for DHNA in CH2Cl2 at B3LYP/6-31+G(d,p) and TD-B3LYP/6-31+G(d,p) levels............. S7
Figure S7. Calculated relative energies (kcal/mol) and wavelengths (nm) of vertical excitation and
emission for DHNA in CH3CN at B3LYP/6-31+G(d,p) and TD-B3LYP/6-31+G(d,p) levels............. S8
Figure S8. Calculated potential energy curves along the TA*  TB* reaction path at
B3LYP/6-31+G(d,p) (S0) and TD-B3LYP/6-31+G(d,p) (S1) levels..................................................... S8
Figure S9. Calculated two-dimensional potential energy (kcal/mol) maps of both ground state (bottom)
and 1st excited state (top) for the proton transfer reactions in the DHNA system in cyclohexane solvent.
The minimum energy path (the solid pink circle) obtained by an IRC calculation was also shown.
The energies were calculated at the B3LYP/6-31+G(d,p) level using the PCM solvation
model..................................................................................................................................................... S9
Figure S10. Calculated two-dimensional potential energy (kcal/mol) maps of both ground state
(bottom) and 1st excited state (top) for the proton transfer reactions in the DHNA system in acetonitrile
solvent. The minimum energy path (the solid pink circle) obtained by an IRC calculation was also
shown. The energies were calculated at the B3LYP/6-31+G(d,p) level using the PCM solvation
model....................................................................................................................................................S10
Eqs. S1.................................................................................................................................................S11
Table S1. Crystal data and structure refinement for DHNA............................................................... S13
Table S2. Bond lengths for the DHNA crystal structure.................................................................... S14
Table S3. Hydrogen bond distances and angles for DHNA crystal structure..................................... S14
Table S4. The photophysical properties of DHNA and 3................................................................... S14
S2
Page
Table S5. Calculated bond lengths (Å) of the normal form (N), tautomer A (TA), and TS1 (N  TA)
on S0 in various solvents......................................................................................................................S15
Table S6. Calculated bond lengths (Å) of the normal form* (N*), tautomer A* (TA*), and TS1* (N*
 TA*) on S1 in various solvents....................................................................................................... S16
Table S7. Calculated bond lengths (Å) of the tautomer A* (TA*), tautomer B* (TB*), and TS2* (TA*
 TB*) on S1 in various solvents........................................................................................................S17
Table S8. Calculated harmonic vibrational frequencies (cm1) of the OH stretching and imaginary
frequencies on S0 in cyclohexane........................................................................................................ S18
Table S9. Calculated harmonic vibrational frequencies (cm1) of the OH stretching and imaginary
frequencies on S1 in cyclohexane........................................................................................................ S19
Calculated Bond Lengths and Stretching Vibrational Frequencies of the OH Bonds...................... S21
Table S10. Calculated Transition State Theory (TST) rate constants (s1) and kinetic isotope effects
(KIEs) at various temperature (K) in cyclohexane.............................................................................. S22
Table S11. Calculated zero-point energy differences (ΔZPEs, ZPETS  ZPEreactant, kcal/mol) in
cyclohexane......................................................................................................................................... S22
Calculated the KIEs at Low Temperature........................................................................................... S23
Low Frequency Modes......................................................................................................................... S23
Table S12. Calculated absorption wavelengths (nm) of the DHNA system in various solvents........ S24
Table S13. Calculated emission wavelengths (nm) of the DHNA system in various solvents.......... S24
S3
Figure S1. Side views of the packing of DHNA in the unit cell.
S4
Figure S2. The 1H NMR spectroscopy of DHNA (up) and HN12(down) in CDCl3.
S5
1.4
1.2
A. U.
1.0
0.8
0.6
0.4
0.2
0.0
300
400
500
Wavelength (nm)
600
Figure S3. Normalized steady-state absorption spectrum (black lines) and excitation spectra (monitor
at 520 nm (red) and 650 nm (blue)) for DHNA in cyclohexane at room temperature. Note that peaks
appearing at ~460 nm and 490-500 nm in the excitation spectrum (monitoring at the 520 nm emission)
are the Raman peaks of the solvent.
1.0
A. U.
0.8
0.6
0.4
0.2
0.0
-1
0
1
2
3
Time (ps)
4
5
Figure S4 Time-resolved femtosecond fluorescence upconversion of DHNA in cyclohexane
monitored at 450 nm (black open square, □, an average of five replicas) and instrument response
function (red).
S6
1.0
Count.
0.8
0.6
0.4
0.2
0.0
0
1
2
3
Time (ns)
4
5
Figure S5. Time-resolved relaxation dynamics of DHNA in solid state monitored at 520 nm (black
open circles, ○), and 650 nm, (blue open square,□). Solid lines depict the corresponding fitting curves
(black and blue) and instrument response function (red).
Figure S6. Calculated relative energies (kcal/mol) and wavelengths (nm) of vertical excitation and
emission for DHNA in CH2Cl2 at B3LYP/6-31+G(d,p) and TD-B3LYP/6-31+G(d,p) levels.
S7
Figure S7. Calculated relative energies (kcal/mol) and wavelengths (nm) of vertical excitation and
emission for DHNA in CH3CN at B3LYP/6-31+G(d,p) and TD-B3LYP/6-31+G(d,p) levels.
Figure S8. Calculated potential energy curves along the TA*  TB* reaction path at
B3LYP/6-31+G(d,p) (S0) and TD-B3LYP/6-31+G(d,p) (S1) levels.
S8
Figure S9. Calculated two-dimensional potential energy (kcal/mol) maps of both ground state (bottom)
and 1st excited state (top) for the proton transfer reactions in the DHNA system in cyclohexane solvent.
The minimum energy path (the solid pink circle) obtained by an IRC calculation was also shown. The
energies were calculated at the B3LYP/6-31+G(d,p) level using the PCM solvation model.
S9
Figure S10. Calculated two-dimensional potential energy (kcal/mol) maps of both ground state
(bottom) and 1st excited state (top) for the proton transfer reactions in the DHNA system in acetonitrile
solvent. The minimum energy path (the solid pink circle) obtained by an IRC calculation was also
shown. The energies were calculated at the B3LYP/6-31+G(d,p) level using the PCM solvation model.
S10
Eqs. S1
In Scheme S1 we also draw a concerted PT pathway (kdpt) but specify that this process is unlikely to
take place according to the kinetic data. This viewpoint is also supported by theoretical arguments
based on the PES landscape, concluding that the concerted PT pathway is thermally unfavorable.
Based on the experimental data we conclude the rate of first proton transfer kpt1 (N* → TA*) to be
faster than the system response of (150 fs)-1. Therefore, in a time frame of several ps of interest, it can
be assumed that at t ~ 0 (< 150 fs) N* has been depopulated to ~zero and TA* is instantaneously
populated (TA* =[TA*]0 at t ~ 0). Therefore, the time-dependent TA* and TB*, specified as [TA*]
and [TB*], respectively, can be expressed as
d[TA*]
 (k fTA*  k pt2 )  [TA*]  k  pt2[TB*]
dt
d[TB*]
 (k fTB*  k  pt2 )  [TB*]  k pt2[TA*]
dt
(1)
(2)
*
where k TfA* and k TB
are the sum of non-ESIPT decay rate for TA* and TB*, respectively. The
f
differential Eqs. (1) and (2) can be solved by Laplace transformation to obtain Eqs. (3) and (4)
[TA*]0
(3)
 [(2  X )  e 1t  ( X  1 )  e 2t ]
2  1
k pt2  [TA *]0
[TB*] 
 [e 1t  e 2t ]
(4)
2  1
1
1, 2  [( X  Y )  ( X  Y ) 2  4  k pt2  k pt 2 ]
Where
(5)
2
*
*
(6)
X  kpt 2  k TA
, Y  kpt 2  k TB
f
f
The experimental results also draw the conclusion that the rate of forward TA*  TB* (kpt2) and
*
reverse TB*  TA* (k-pt2) proton transfer is much larger than k TfA* and k TB
. Under the condition of
f
[TA*] 
S11
*
*
, it is thus reasonable for us to claim the pseudo equilibrium between TA* and
kpt2 , k-pt2  k TA
, k TB
f
f
TB* prior to their corresponding emission. As a result, X  k pt2 and Y  k  pt2 and 1 and2 in Eqs. (5)
can be written as follows.
1 
1
1

*
*
k TA
 k pt 2  k TB
 k pt 2
f
f
k pt 2  k pt 2

*
*
k TA
 k TB
f
f K eq
1  K eq
, 2 
1
2
 kpt2  kpt2
(7)
The pre-exponential factors in Eqs. (3) for the [TA*] can be derived further as
A1 
k pt2
[TA *]0  ( X  1 )

2  1
k pt2  k pt2
(8)
A2 
k  pt2
[TA *]0  (2  X )

2  1
k pt2  k  pt2
(9)
The ratio between A1 and A2, i.e. A1/A2 is thus derived to be kpt2/k-pt2, which is equivalent to the
equilibrium constant Keq (= kpt2/k-pt2) between TB* and TA* species. We then further convert the
time-resolved concentration expression (Eqs. (3) and (4)) to the time-resolved fluorescence intensity of
TA* and TB*, denoted as [TA*]f and [TB*]f. This is done by multiplying the instrument factor (I0) and
the fluorescence radiative decay rate constant k rTA * and k rTB * for TA* and TB*, respectively, giving
Eqs. (10) and (11), which is essentially identical with equation (I) in the text.
[TA*] f 
[TB*] f 
I 0  k rTA *  [TA*]0
 [( 2  X )  e 1t  ( X  1 )  e 2t ]
2  1
I 0  k rTB *  k pt2  [TA *]0
2  1
 [e 1t  e 2t ]
(10)
(11)
S12
Table S1. Crystal data and structure refinement for DHNA
Empirical formula
C11 H8 O3
Formula weight
188.17
Temperature
200(2) K
Wavelength
0.71073 Å
Crystal system
Monoclinic
Space group
P2(1)/c
Unit cell dimensions
a = 8.4818(10) Å
= 90°.
b = 6.7611(8) Å
= 105.173(2)°.
c = 14.9995(17) Å
 = 90°.
Volume
830.18(17) Å3
Z
4
Density (calculated)
1.506 Mg/m3
Absorption coefficient
0.110 mm-1
F(000)
392
Crystal size
0.42 x 0.30 x 0.10 mm3
Theta range for data collection
2.49 to 27.50°.
Index ranges
-11<=h<=11, -8<=k<=8, -19<=l<=19
Reflections collected
7218
Independent reflections
1905 [R(int) = 0.0292]
Completeness to theta = 27.50°
100.0 %
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.9891 and 0.9551
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
1905 / 0 / 135
Goodness-of-fit on F2
1.057
Final R indices [I>2sigma(I)]
R1 = 0.0504, wR2 = 0.1429
R indices (all data)
R1 = 0.0667, wR2 = 0.1575
Largest diff. peak and hole
0.297 and -0.293 e.Å-3
S13
Table S2. Bond lengths for the DHNA crystal structure
Bond Lengths (Å)
O(1)-C(11)
1.2303(18)
C(5)-C(10)
1.424(2)
O(2)-C(7)
1.3503(16)
C(5)-C(6)
1.4271(19)
O(3)-C(1)
1.3560(18)
C(6)-C(7)
1.4269(19)
C(1)-C(2)
1.380(2)
C(7)-C(8)
1.386(2)
C(1)-C(6)
1.4221(19)
C(8)-C(9)
1.4155(19)
C(2)-C(3)
1.391(2)
C(8)-C(11)
1.4409(19)
C(3)-C(4)
1.367(2)
C(9)-C(10)
1.355(2)
C(4)-C(5)
1.4098(19)
Table S3. Hydrogen bond distances and angles for DHNA crystal structure
D-H∙∙∙A
d(D-H)/Å
d(H∙∙∙A)/Å
d(D∙∙∙A)/ Å
<(DHA)/ °
O(2)-H(2)...O(1)
0.92(2)
1.73(2)
2.5603(14)
148(2)
O(3)-H(3)...O(2)
0.87(2)
1.90(2)
2.6433(15)
143(2)
Table S4. The photophysical properties of DHNA and 3
Compounds
observed λabs/nm
(ε/M−1 cm−1)
λmonitor/nm
Q. Y (%)
τobs(pre-exp. factor)
DHNA
400 (1.1  104)
520
650
0.24
1.1 ± 0.2 psa (0.68); 53 ± 3.6 psa,b (0.32)
1.1 ± 0.3psa (-0.43); 54 ± 3.2 ps a,b (0.57)
3
365 (5.5  103)
450
0.26
1.75 nsc
520
650
5.0
228 ± 20 psb
223 ± 22 psb
DHNA (solid)
a.
The lifetime was measured using an ultrafast fluorescence upconversion technique.
Lifetime was measured by a TCSPC system with femtosecond excitation pulses.
c. Lifetime was measured by a TCSPC system with a pulsed hydrogen-filled lamp as the excitation source.
b.
S14
Table S5. Calculated bond lengths (Å) of the normal form (N), tautomer A (TA), and TS1 (N  TA) on S0 in various solvents
normal form (N)
tautomer A (TA)
TS1 (N  TA)
cyclohexane CH2Cl2
CH3CN cyclohexane CH2Cl2
CH3CN cyclohexane CH2Cl2
CH3CN
O(3)H(3)
0.975
0.976
0.976
0.983
0.983
0.984
0.990
0.991
0.992
O(2)H(3)
1.786
1.783
1.781
1.748
1.742
1.740
1.693
1.683
1.680
O(2)H(2)
1.009
1.008
1.008
1.236
1.234
1.234
1.547
1.550
1.551
O(1)H(2)
1.604
1.609
1.610
1.179
1.179
1.179
1.023
1.022
1.022
C(1)O(3)
1.356
1.358
1.359
1.351
1.354
1.355
1.347
1.350
1.352
C(7)O(2)
1.348
1.349
1.349
1.313
1.314
1.315
1.287
1.289
1.289
C(11)O(1)
1.248
1.249
1.250
1.284
1.285
1.286
1.311
1.312
1.312
S15
Table S6. Calculated bond lengths (Å) of the normal form* (N*), tautomer A* (TA*), and TS1* (N*  TA*) on S1 in various solvents
normal form* (N*)
tautomer A* (TA*)
TS1* (N*  TA*)
cyclohexane CH2Cl2
CH3CN cyclohexane CH2Cl2
CH3CN cyclohexane CH2Cl2
CH3CN
O(3)H(3)
0.990
0.987
0.987
0.996
0.994
0.993
1.021
1.020
1.020
O(2)H(3)
1.718
1.732
1.736
1.687
1.698
1.700
1.565
1.565
1.565
O(2)H(2)
1.053
1.048
1.047
1.158
1.154
1.154
1.608
1.614
1.615
O(1)H(2)
1.477
1.487
1.489
1.282
1.285
1.284
1.017
1.014
1.014
C(1)O(3)
1.338
1.340
1.340
1.337
1.340
1.341
1.334
1.337
1.338
C(7)O(2)
1.359
1.359
1.359
1.346
1.347
1.347
1.317
1.318
1.319
C(11)O(1)
1.286
1.292
1.294
1.299
1.306
1.307
1.330
1.335
1.337
S16
Table S7. Calculated bond lengths (Å) of the tautomer A* (TA*), tautomer B* (TB*), and TS2* (TA*  TB*) on S1 in various solvents
tautomer A* (TA*)
tautomer B* (TB*)
TS2* (TA*  TB*)
cyclohexane CH2Cl2
CH3CN cyclohexane CH2Cl2
CH3CN cyclohexane CH2Cl2
CH3CN
O(3)H(3)
1.021
1.020
1.020
1.269
1.228
1.221
1.450
1.512
1.526
O(2)H(3)
1.565
1.565
1.565
1.168
1.200
1.205
1.062
1.037
1.032
O(2)H(2)
1.608
1.614
1.615
1.729
1.730
1.730
1.766
1.786
1.791
O(1)H(2)
1.017
1.014
1.014
0.995
0.995
0.995
0.990
0.986
0.986
C(1)O(3)
1.334
1.337
1.338
1.307
1.312
1.314
1.295
1.295
1.295
C(7)O(2)
1.317
1.318
1.319
1.343
1.343
1.343
1.354
1.359
1.360
C(11)O(1)
1.330
1.335
1.337
1.330
1.336
1.338
1.329
1.333
1.335
S17
Table S8. Calculated harmonic vibrational frequencies (cm1) of the OH stretching and imaginary frequencies on S0 in cyclohexane
normal form (N)
tautomer A (TA)
TS1 (N  TA)
2977
(O(2)H(2) and C(11)H(11)
asymmetric stretching)
3022
(O(2)H(2) and C(11)H(11)
symmetric stretching)
3645
(O(3)H(3) stretching)
1015 i
(Imaginary frequency)
2774
(O(2)H(2) stretching)
3125 (C(11)H(11) stretching)
3183 (C(11)H(11) stretching)
3493
3345
(O(3)H(3) stretching)
(O(3)H(3) stretching)
H(2) and H(3) substituted by deuterium
2977
(O(2)D(2) stretching)
756 i
(Imaginary frequency)
2037
(O(2)D(2) stretching)
2654
(O(3)D(3) stretching)
2545
(O(3)D(3) stretching)
2439
(O(3)D(3) stretching)
S18
Table S9. Calculated harmonic vibrational frequencies (cm1) of the OH stretching and imaginary frequencies on S1 in cyclohexane
normal form* (N*)
tautomer A* (TA*)
TS1* (N*  TA*)
2309
(O(2)H(2) stretching)
766 i
(Imaginary frequency)
2756
(O(1)H(2) and O(3)H(3)
asymmetric stretching)
3370
(O(3)H(3) stretching)
3247
(O(3)H(3) stretching)
2889
(O(1)H(2) and O(3)H(3)
symmetric stretching)
H(2) and H(3) substituted by deuterium
1720
(O(2)D(2) stretching)
574 i
(Imaginary frequency)
2018
(O(1)D(2) and O(3)D(3)
asymmetric stretching)
2457
(O(3)D(3) stretching)
2369
(O(3)D(3) stretching)
2116
(O(1)D(2) and O(3)D(3)
symmetric stretching)
S19
Table S9. Continued
tautomer A* (TA*)
TS2* (TA*  TB*)
tautomer B* (TB*)
2756
(O(1)H(2) and O(3)H(3)
stretching)
751 i
(Imaginary frequency)
2237
(O(2)H(3) stretching)
2889
(O(1)H(2) and O(3)H(3)
stretching)
3284
(O(1)H(2) stretching)
3398
(O(1)H(2) stretching)
H(2) and H(3) substituted by deuterium
2018
(O(1)D(2) and O(3)D(3)
asymmetric stretching)
558 i
(Imaginary frequency)
1670
(O(2)D(3) stretching)
2116
(O(1)D(2) and O(3)D(3)
symmetric stretching)
2391
(O(1)D(2) stretching)
2474
(O(1)D(2) stretching)
S20
Calculated Bond Lengths and Stretching Vibrational Frequencies of the OH Bonds
As shown in Table S5, the O(3)H(3) bond lengths of the N, TS1, and TA on the ground state (S0)
in cyclohexane were calculated to be 0.975, 0.983, and 0.990 Å, respectively. On the other hand, the
calculated O(3)H(3) stretching vibrational frequencies of these conformations on S0 were 3645, 3493,
and 3345 cm1, respectively (see Table S8). The OH bond strengths were significantly affected by
the corresponding H(3)hydrogen bond strengths. The hydrogen bond strength increases from N,
TS1, to TA, so the O(3)H(3) bond length increases and the O(3)H(3) stretching frequency decreases
from N to TA.
On the 1st singlet excited state (S1), the N*, TS1*, and TA* in cyclohexane were predicted to have
stronger O(2)…H(3) hydrogen bond than those on S0. The O(3)H(3) bond lengths were calculated to
be 0.990, 0.996, and 1.021 Å (Table S6), respectively. The calculated O(3)H(3) stretching vibrational
frequencies of these conformations on S1 were 3370, 3247, and 2889 cm1 (Table S9) which are
significantly lower than those on S0. We noticed that the bond length of the O(3)H(3) in TA* was
nearly the same as that of O(1)H(2) (1.017 Å), but they are quite different in TA. The O(2)H(2)
bond length (1.053 Å) in N* is very long because of the very strong O(1)…H(2) hydrogen bond. The
corresponding OH stretching frequency is only 2309 cm1 which is even lower than the O(3)D(3)
frequency in TA*.
The O(2)H(3) in TB* was predicted to be the longest OH bond (1.062 Å) and with the lowest
vibrational frequency (2237 cm1). It suggested that O(3)…H(3) in TB* is the strongest hydrogen
bond in the current system. The O(2)D(3) frequency in TB* was predicted to be as low as 1670 cm1.
S21
Table S10. Calculated Transition State Theory (TST) rate constants (s1) and kinetic isotope effects
(KIEs) at various temperature (K) in cyclohexane
Temperature
N  TA
N*  TA*
TA*  TB*
200 K
1.12 × 1012
1.59 × 1014
2.61 × 1012
250 K
1.55 × 1012
8.48 × 1013
3.30 × 1012
303 K
1.96 × 1012
5.53 × 1013
3.95 × 1012
Rate constant
H(2) and H(3) replaced by deuterium
Rate constant
KIE
200 K
1.63 × 1011
3.70 × 1013
5.00 × 1011
250 K
3.24 × 1011
2.60 × 1013
8.72 × 1011
303 K
5.24 × 1011
2.05 × 1013
1.31 × 1012
200 K
6.89
4.31
5.23
250 K
4.79
3.26
3.78
303 K
3.74
2.69
3.02
Table S11. Calculated zero-point energy differences (ΔZPEs, ZPETS  ZPEreactant, kcal/mol) in
cyclohexane
ΔZPEH
N  TA
N*  TA*
TA*  TB*






ΔZPED represents the calculated ZPEs for the H(2) and H(3) replaced by deuterium
ΔZPEDa
a
S22
Calculated the KIEs at Low Temperature
The absence of measured KIEs on S1 suggested that the reaction bottleneck might not be located
at the TS where the transferred hydrogen atom moves from the donor to the acceptor. Instead, we
suspect that the bottleneck might be mainly related to the entropic effects due to the excited
large-amplitude bending or twisting vibrations of the TA* which may easily disrupt the hydrogen
boding along which the proton transfer occur. At lower temperature, the entropic effects are supposed
to be less important and the TS might become the reaction bottleneck if the low-frequency
large-amplitude motions can be quenched more effectively. The calculated KIEs by TST theory at 250
and 200 K were 3.8 and 5.2, respectively, which are significantly larger than the value at 303 K. There
is a chance that the deuterium KIEs can be observed at lower temperature.
Low Frequency Modes
Using an ultrashort pulse of e.g. <10 fs pulse, the oscillation of time-resolved signal at early time
has been occasionally resolved for several ESIPT system via fluorescence upconversion or transient
absorption. For these cases, the time-domain signal can be Fourier transformed to frequency-domain to
obtain the corresponding low frequency motions that modulate the hydrogen bond and hence induce
ESIPT. Experimentally we have been trying very hard in attempts to resolve the possible early time
oscillation but unfortunately in vain. This may be due to a much longer pulse excitation (~120 fs) used
in the current experimental setup, together with relatively low signal to noise ratio. On the other hand,
from the computational approaches, it is hard to pin down which modes exactly cause the slower rate
constants and the absence of the KIEs. It is reasonable to assume that upon excitation, some of the low
frequency modes such as the various low-frequency ring bending and twisting modes are in highly
excited states and exhibit large amplitude motions. These motions may easily modulate/disrupt the
hydrogen bonding along which the proton transfer occurs. In the current case, all the modes below 200
cm-1 (3 in total: 76, 113, and 168 cm-1) of TA* are susceptible. In the language of thermodynamics,
TA* may have a much lower free energy (larger entropy) than expected and thus the TS is harder to
reach and the rate constants are lower than those as expected based on the equilibrium distribution.
Since these large amplitude motions are not sensitive to the mass of the hydrogen being transferred, so
no KIEs were observed.
S23
Table S12. Calculated absorption wavelengths (nm) of the DHNA system in various solvents
cyclohexane CH2Cl2 CH3CN
N
TA
407
427
407
427
405
425
TD-B3LYP/6-311+G(2df,2pd)// N
B3LYP/6-31+G(d,p)
TA
409
429
410
431
409
429
TD-B3LYP/6-31+G(d,p)
Table S13. Calculated emission wavelengths (nm) of the DHNA system in various solvents
cyclohexane CH2Cl2 CH3CN
N*
TA*
TB*
459
498
599
466
506
618
469
509
622
N*
TD-B3LYP/6-311+G(2df,2pd)//
TA*
TD-B3LYP/6-31+G(d,p)
TB*
464
503
605
460
496
597
458
493
590
TD-B3LYP/6-31+G(d,p)
S24