Energy and Electron Transfer
in Ethynylene Bridged Perylene Diimide
Multichromophores
Cristina Flors, Ingo Oesterling, Tobias Schnitzler, Eduard Fron,
Gerd Schweitzer, Michel Sliwa, Andreas Herrmann, Mark van
der Auweraer, Frans C. de Schryver, Klaus Mullen,
and Johan Hofkens
J.Phys.Chem.C. 2007, 111, 4861-4870
Kou ITOH
MIYASAKA Lab.
Contents
● Background
● Method – explanation of measurement technique
time-resolved spectroscopy (ensemble)
single-molecule spectroscopy
● Results and discussion
Steady-state measurement
Florescence decay measurement
Femtosecond transient absorption spectroscopy
Single-Molecule detection
● Conclusion
Background
Novel photonic devices consisting of molecular systems
●
single photon source
●
artificial light-harvesting system
single photon source
etc.
artificial light-harvesting system
light
light
pulse
Single
photon
energy
Chromophore :
J.P.C.B.2004,108,16686-16696
J.A.C.S.2007,129,3539-3544
Evaluation and understanding of the molecular photonic
devices
Ensemble measurements
Single molecule measurements
Dynamics, Efficiency of
• Energy transfer
• Electron transfer
• Emission lifetime etc.
• Emission dynamics of
individual molecular systems
• Ultra-high temporal resolution
• Reliable average values
Enables us to evaluate single
nanoscale photonic devices
• Photon antibunching
Complementary use of both measuring methods can give us
comprehensive understanding of the nanoscale-molecular devices
Method 1):
ensemble time-resolved measurement
Charge separation
①
count
S1
hν
S0
Fluorescence decay
Pump light
detector
T
Probe light
T: delay time
sample
Delta A
②
time/ns
fluorescence
Wavelength/nm
Transient absorption spectra
counts
Method 2):
single-molecule spectroscopy
Time/ns
Fluorescence decay
counts
Events
imaging
Time/s
Fluorescence intensity
trajectory
Delay/ns
coincidence
Molecular structure of PDI derivatives
Ａ
:bay area
Perylene-3,4,9,10tetracarboxdiimide
(PDI)
C
ＰＤＩ０
B
Steady-state measurement
in toluene
Summery of the photophysical properties of Ａ－Ｃ in solution
A: black
B: red
C: blue
(in toluene)
A
Compound
A
B
C
λmax,
abs,nm
573
573
573
λmax,
emi,nm
604
602
602
ΦF
0.99
1.00
1.00
in THF
scheme
S1
S0
Charge Separation
Compound
A
B
C
λmax,
abs,nm
569
568
589
λmax,
emi,nm
601
601
600
ΦF
0.42
0.11
0.96
B
:
Diphenylacetylene
group(electron donor)
Fluorescence decay measurement
C
B
nitrogen
C(THF)
A(THF)
B(THF)
oxygen
Ａ
Fluorescence decay (time constant)
Toluene τF[ns]
THF
τF[ns]
A
B
C
5.1
5.3
5.3
1.0(14%)
2.8(86%）
1.1
5.6
Time-resolved fluorescence depolarization
A
B
Toluene Q1[ns]
Q2 [ps]
3.1
110
0.56
---
Q1 [ns]
Q2 [ps]
3.1
53
0.38
---
THF
C
tF: 1.0 ns
tF ~ 2.8 ns
Electron transfer from a
diphenylacetylene group
Through-space electron transfer
Femtosecond transient absorption spectroscopy ①
PDI0
Lifetime
Compound B
S1
ＰＤＩ０
B
5ns
185ps,1ns
185ps
1.1ns
(Slide 9)
1ns
S0
Transient absorption spectra in THF of PDI0(A)
And B(B) at 2(black),10(red),50(green),100(blue)
200(purple),and 400ps(brown).
Radical
anion
Summary of the ensemble measurements
Electron
Transfer
Toluene
THF
A
×
○
B
×
○
C
×
×
●Femtosecond transient absorption measurement
The dynamics of generation and decay about PDI radical
anion was revealed. (in more polar solvent)
Single-Molecule measurement : Results①
Beam splitter
APD1
Channel A
fluorescence
APD2
Off
time
Channel B
Single-molecule intensity trace of Ａ in PMMA
Channel A (gray) and B (black) correspond to
Polarization directions perpendicular in each other.
1:stepwise change → the emitting chromophoric site is changing with time.
2:fluctuating trace → intersystem crossing from singlet to triplet by oxygen
3:off time → influence of charge separation
Single-Molecule measurement (Coincidence)
J.P.C.B 2004,108,16686-16696
Jpn.J.Appl.Phys 2007,46,268-270
Fluorescence from the sample
Repetition period ~ 125ns
： Photon
sample
APD1
APD1
APD2
APD2
Single-photon emitting source
1 pulse → 1 photon
NL
Interphoton
arrival time
Coincidence
NL
Antibunching
NC
N /N ~ 0.2
M
NC/NL ratio
1
0
2
0.5
3
0.67
4
0.75
NC/NL = 1－( 1 / M )
NC : number of central position
NL : number of lateral positions
M : number of photons / 1 pulse
Single-Molecule measurement : results②
S1-S1 annihilation
S1* + S1*
→
So + S1*
Sｎ
S１
S１
S０
S０
Compound A
Fluorescence trajectory of single-molecule (A)
and fluctuation of Nc/NL ratio
J.Phys,:.Condens.Matter. 2007,19,445004
Conclusion
The authors synthesized a multichromophoric system as a
candidate for single photon source and measured the property of
the emission.
Steady state and time-resolved ensemble measurement revealed
that charge transfer can take place in the multi-chromophoric
compound in relatively polar environment; polarity affects the
emission property of compound A.
The time-resolved measurement also suggested that energymigration as well as the charge transfer.
The efficient energy migration was confirmed by measuring the
photon-antibunching of compound; the compound worked as
“single photon emitter”.

ICGM - IMS

Reduction