Supporting Information Exciton delocalization and dynamics ... · Supporting Information Exciton...

1

Supporting Information

Exciton delocalization and dynamics in helical π-stacks

of self-assembled perylene bisimides

Jong Min Lim,a Pyosang Kim,a Min-Chul Yoon,a Jooyoung Sung,a Volker Dehm,b Zhijian Chen,b,c Frank

Würthner,*,b and Dongho Kim*,a

aDepartment of Chemistry, Yonsei University, Seoul, 120-749, Korea, bInstitut für Organische Chemie

& Center for Nanosystems Chemistry, Universität Würzburg, Würzburg, 97074, Germany, and cSchool

of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China

[email protected], [email protected]

RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required

according to the journal that you are submitting your paper to)

Electronic Supplementary Material (ESI) for Chemical ScienceThis journal is © The Royal Society of Chemistry 2012

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EXPERIMENTAL METHODS

Sample preparation Tetracarboxylic acid bisimide (PBI) dyes 1, 2, 3, and 4 were synthesized

according to previously reported procedures.1-3 In all spectroscopic experiments, chloroform and

methylcyclohexane were used as solvent (Sigma-Aldrich, spectrophotometric grade) without further

purification. For quencher embedment experiments, standard solution of PBI dyes 1 and 4 are prepared

in chloroform solvent. After mixing two standard solutions of PBI 1 and 4 with proper ratios (1000, 100,

10, and 5 versus 1), chloroform solvent was evaporated and the hetero-PBI dyes were dissolved in

methylcyclohexane solvent. By using this solution of hetero-PBI dyes, we have examined the

fluorescence spectra and the pump-power dependency in fs-transient absorption measurements.

Steady-state absorption and fluorescence measurements UV-vis spectra were recorded with a

Varian Cary 5000 UV-Vis-NIR spectrophotometer and fluorescence spectra were recorded with a

Hitachi model F-2500 fluorescence spectrophotometer.

Fluorescence lifetime and time-resolved fluorescence anisotropy A time-correlated single-photon-

counting (TCSPC) system was used for measurements of spontaneous fluorescence decay and

fluorescence anisotropy decay. As an excitation light source, we used a mode-locked Ti:sapphire laser

(Spectra Physics, MaiTai BB) which provides ultrashort pulse (80 fs at full width half maximum, fwhm)

with high repetition rate (80 MHz). This high repetition rate slows down to 1M ~ 800 kHz by using

homemade pulse-picker. The pulse-picked output pulse was frequency-doubled by a 1 mm thickness of

a BBO crystal (EKSMA). The fluorescence was collected by a microchannel plate photomultiplier

(MCP-PMT, Hamamatsu, R3809U-51) with a thermoelectric cooler (Hamamatsu, C4878) connected to

a TCSPC board (Becker&Hickel SPC-130). The overall instrumental response function was about 25 ps

(fwhm). A vertically polarized pump pulse by a Glan-laser polarizer was irradiated to samples, and a

sheet polarizer, set at an angle complementary to the magic angle (54.7°), was placed in the

fluorescence collection path to obtain polarization-independent fluorescence decays.

Femtosecond transient absorption measurement Femtosecond (fs) time-resolved transient

absorption (TA) spectra were recorded using a spectrometer consisting of a homemade noncollinear

optical parametric amplifier (NOPA) pumped by a Ti:sapphire regenerative amplifier system


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(Quantronix, Integra-C) operating at 1 kHz repetition rate coupled with an optical detection system. The

generated visible NOPA pulses had a pulse width of ~ 100 fs and an average power of 1 mW in the

range 480-700 nm, which were used as pump pulses. White light continuum (WLC) probe pulses were

generated using a sapphire window (2 mm of thickness) by focusing of small portion of the fundamental

800 nm pulses that were picked off by a quartz plate before entering into the NOPA. The time delay

between pump and probe beams was carefully controlled by causing the pump beam to travel along a

variable optical delay (Newport, ILS250). Intensities of the spectrally dispersed WLC probe pulses are

monitored by a miniature spectrograph (OceanOptics USB2000+). To obtain the time-resolved transient

absorption difference signal (ΔA) at a specific time, the pump pulses were chopped at 25 Hz and the

absorption spectra intensities were saved alternately with or without pump pulse. Typically, 6000 pulses

were used to excite the samples so as to obtain a TA spectra at a particular delay time. The polarization

angle between the pump and probe beams was set at the magic angle (54.7°) using a Glan-laser

polarizer with a half-wave retarder so as to prevent polarization-dependent signals. The cross-

correlation fwhm in the pump-probe experiments was less than 200 fs and the chirp of WLC probe

pulses was measured to be 800 fs in the 400-1250 nm region. To minimize chirp, all-reflection optics in

the probe beam path and a 2 mm path length quartz cell were used. After the TA experiments, the

absorption spectra of all compounds was carefully checked so as to avoid artifacts arising from, e.g.,

photo-degradation or photo-oxidation of the samples in question. HPLC grade solvents were used in all

steady-state and time-resolved spectroscopic studies.

Femtosecond transient absorption anisotropy decay Dual-beam femtosecond time-resolved

transient absorption (TA) spectrometer consisted of two independently-tunable home-made noncollinear

optical parametric amplifiers (NOPA) pumped by a regeneratively amplified Ti:sapphire laser system

(Spectra-Physics, Hurricane-X) operating at 3 kHz repetition rate and an optical detection system. The

NOPA was based on non-collinearly phase-matching geometry, which was easily color-tuned by

controlling optical delay between white light continuum seed pulses (450-1400 nm) and visible pump

pulses (400 nm) produced by using a sapphire window and BBO crystal, respectively. The generated


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visible OPA pulses had a pulse width of ~ 35 fs and an average power of 10 mW at 3 kHz repetition rate

in the range 500-700 nm after a fused-silica prism compressor. Two OPA pulses were used as the pump

and probe pulses, respectively, for TA measurement. The probe beam was split into two parts. The one

part of the probe beam was overlapped with the pump beam at the sample to monitor the transient

(signal), while the other part of the probe beam was passed through the sample without overlapping the

pump beam to compensate the fluctuation of probe beam. The time delay between pump and probe

beams was carefully controlled by making the pump beam travel along a variable optical delay

(Newport, ILS250). To obtain the time-resolved transient absorption difference signal at specific

wavelength, the monitoring wavelength was selected by using a narrow interference filter (FWHM ~10

nm). By chopping the pump pulses at 47 Hz, the modulated probe pulses as well as the reference pulses

were detected by two separate photodiodes (New Focus, Femtowatt Photoreceiver). The modulated

signals of the probe pulses were measured by a gated-integrator (SRS, SR250) and a lock-in amplifier

(EG&G, DSP7265) and stored in a personal computer for further signal processing. In general

experimental conditions, time-resolutions of less than 50 fs were achieved. For anisotropy

measurement, both I|| and I⊥ signals were collected simultaneously by combination of polarizing beam-

splitter cube and dual lock-in amplifiers as following equation:4

)2/(()()( |||| ⊥⊥ +−= IIIItr

where I|| and I⊥ represent TA signals with the polarization of the pump and probe pulses being

mutually parallel and perpendicular respectively. The pump pulse was set to vertical polarization and

that of probe pulse was set to 45° with respect to the pump pulse by using Glan-laser polarizers and

half-wave plates. After the probe pulse passes through the sample cell, it was split by a polarizing beam-

splitter cube and then detected by two separate photodiodes. Two gated-integrators and two lock-in

amplifiers record the signal simultaneously within a single scan. As a standard anisotropy measurement

showed a clean single exponential decay with reorientational relaxation times of 122.1 ± 0.3 ps and the

initial anisotropy r(0) value of 0.39 ± 0.02 for rhodamine 6G dye in methanol, which are well-matched in

other reference.5 For all TAA measurements, wavelength of pump and probe pulses were set to 550 nm


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with an average power of less than 40 μW and 690 nm, respectively. A thin absorption cell with a

pathlength of 500 μm was used to eliminate additional chirping.

Fluorescence up-conversion spectroscopy A femtosecond fluorescence up-conversion apparatus

was used for the time-resolved spontaneous fluorescence. As an excitation light source, we used a

mode-locked Ti:sapphire laser (Spectra Physics, MaiTai BB) which provides ultrashort pulse (80 fs at

full width half maximum, fwhm) with high repetition rate (80 MHz). The second harmonic of the

fundamental generated by a 200-μm thick BBO crystal served as pump pulse. Residual fundamental

pulse was used as a gate pulse. The pump beam was focused onto a 500-μm thick quartz cuvette

containing sample solution using a 5-cm focal length plano-convex lens with a magic angle (54.7°) in

order to prevent polarization-dependent signals. The cuvette was mounted on a motor-driven stage and

moved constantly back and forth to minimize photo-degradation. Collection of the fluorescence and

focusing into a 500 μmm-thick BBO crystal for frequency conversion was achieved by a reflecting

microscope objective lens (Coherent). The FWHM of the cross-correlation function between the

scattered pump pulse and the gate pulse is measured to be ~340 fs. The average excitation power was

kept at a level below 2 mW in order to minimize thermal lens effect. In this excitation intensity regime

the fluorescence dynamics was be independent of the excitation intensity for all samples.

References

1) Z. Chen, V. Stepanenko, V. Dehm, P. Prins, L. D. A. Siebbeles, J. Seibt, P. Marquetand, V. Engel

and F. Würthner, Chem. Eur. J, 2007, 13, 436-449.

2) Z. Chen, U. Baumeister, C. Tschierske and F. Würthner, Chem. Eur. J, 2007, 13, 450-465.

3) F. Würthner, C. Thalacker, S. Diele and C. Tschierske, Chem. Eur. J, 2001, 7, 2245-2253.

4) C. K. Min, T. Joo, M.-C. Yoon, C. M. Kim, Y. N. Hwang, D. Kim, N. Aratani, N. Yoshida and A.

Osuka, J. Chem. Phys., 2001, 114, 6750-6758.

5) L. A. Philips, S. P. Webb, S. W. Yeh and J. H. Clark, J. Phys. Chem., 1985, 89, 17-19.


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350 400 450 500 550 600 650 700 750

PBI 3

PBI 2

PBI 1

PBI 4

Flu

orescen

ce Inten

sity (No

rm.)

Wavelength (nm)

Ab

sorb

ance

(N

orm

.)

350 400 450 500 550 600 650 700 750

Flu

orescen

ce Inten

sity (No

rm.)

Ab

sorb

ance

(N

orm

.)

PBI 4

PBI 3

PBI 2

PBI 1

Wavelength (nm)

a)

b)

Fig. S1 Steady-state absorption spectra and fluorescence emission of PBI 1, PBI 2, PBI 3, and PBI 4 in

a) chloroform (~10-6 M) and b) methylcyclohexane (~10-3 M).


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0 20 40 60 80 1000.01

0.1

1

In

ten

sit

y(a

.u.)

Time (ns)

τ1 τ2

10-5 M 3.30 (17.3%) 40.92 (82.7%)

6.7*10-6 M 3.21 (29.3%) 40.25 (70.7%)

5*10-6 M 3.30 (38.0%) 39.95 (62%)

3.4*10-6 M 3.18 (49.6%) 38.69 (50.4%)

2*10-6 M 3.00 (67.2%) 36.16 (32.8%)

1.4*10-6 M 3.23 (79.0%) 34.03 (21.0%)

10-6 M 3.08 (83.6%) 32.91 (16.4%)

Fig. S2 Concentration dependent fluorescence decay profiles of PBI 1 in methylcyclohexane. The

shorter time components are correspond to the PBI monomer and the longer ones represent the

fluorescence lifetime of aggregates forms.


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~200 ps

~300 ps ~300 ps

0.0 0.5 1.0 1.5 2.00.0

0.2

0.4

0.6

0.8

1.0

1.2

In

ten

sity

(N

orm

.)

Time (ns)

10-7 Mλprobe = 650 nm

0.0 0.5 1.0 1.5 2.00.0

0.2

0.4

0.6

0.8

1.0

1.2

Inte

nsi

ty (

No

rm.)

Time (ns)


0.0 0.5 1.0 1.5 2.00.0

0.2

0.4

0.6

0.8

1.0

1.2

Inte

ns

ity

(N

orm

.)

Time (ns)


0.0 0.5 1.0 1.5 2.00.0

0.2

0.4

0.6

0.8

1.0

1.2

Inte

ns

ity

(N

orm

.)

Time (ns)


a) b)

c) d)

~200 ps

Fig. S3 Concentration dependent fluorescence rise and decay profiles of PBI 1 in methylcyclohexane.

The excimer fluorescence emission signals are observed at 650 and 700 nm.


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0 10 20 30 40 50 60

0.0

0.2

0.4

0.0

0.2

0.4

0.0

0.2

0.4

0.0

0.2

0.4

10-3 M

Time (ns)

λex = 450 nm

λprobe = 700 nm

10-6 M

3.4 X10-6 M

An

iso

tro

py

10-5 M

Fig. S4 Concentration dependent fluorescence anisotropy changes of PBI 1 in methylcyclohexane.


10

0 2 4 6 8 10

0.0

0.2

0.4 τrot

= 1.5 ns

An

iso

tro

py

Time (ns)

0 2 4 6 8 10 12 14 16 18 20 22 240.0

0.2

0.4

0.6

0.8

1.0

τf = 3 ns

Inte

nsi

ty (

No

rm.)

Time (ns)

a)

b)

Fig. S5 Fluorescence (a) and anisotropy decay (b) profiles of PBI 1 (10-7 M) in methylcyclohexane.

Fluorescence and anisotropy decay profiles are observed at 520 and 700 nm, respectively.


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0 20 40 60 80 100

40

80

120

160

F

luo

resc

ence

Inte

nsi

ty

Time (ps)

τ (ps) = 0.8 (38.4 %) 19.3 (25.6 %) long (42.3 %)

in methylcyclohexaneλprobe

= 580 nm

Fig. S6 Fluorescence decay profile of PBI 2 (10-3 M) at 580 nm.


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450 500 550 600 650 700 750 800 850

-0.3

-0.2

-0.1

0.0

0.1

0.2

0 500 1000 1500 2000 2500 3000

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

τs = 1.4 ns

λpump

= 530 nm

Time (ps)

λprobe

(nm) =

490 704

in CHCl3

λpump

= 530 nm

Δ

OD

Wavelength (nm)

Time (ps) -2 1 10 300 500 1000 2000 3000

Fig. S7 Femtosecond transient absorption spectra and decay profiles (inest)of PBI 1 in chloroform.


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450 500 550 600 650 700 750

-0.2

-0.1

0.0

0.1in CHCl

3λ

pump = 550 nm

0 500 1000 1500 2000 2500 3000-0.10

-0.05

0.00

0.05

0.10

0.15

Time (ps)

λprobe

=

511 nm 704 nm

Δ

OD

Wavelength (nm)

Time (ps) -1 1

50 100 200 300 500 1000 2000 3000

τs = 2 ns

Fig. S8 Femtosecond transient absorption spectra and decay profiles (inest) of PBI 2 in chloroform. The

time profile shows single exponential decay curve and the singlet excited-state lifetime is estimated to

be 2 ns.


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450 500 550 600 650 700 750 800 850

-0.2

0.0

0.2

in CHCl3

λpump

= 520 nm

-5 0 5 10 15 20 25 30 35 40 45 50 55 600.0

0.1

0.2

0.3

λprobe

= 700 nm

τS = 10 ps

Δ O

D

Time (ps)

Δ O

D

Wavelength (nm)

Time (ps) -2 1 2 3 4 5 6

7 8 9 10 13 15 20 25 30 50

450 500 550 600 650 700 750 800 850-0.2

0.0

0.2in MCHλ

pump = 520 nm

-5 0 5 10 15 20 25 30 35 40 45 50 55 60

-0.20

-0.15

-0.10

-0.05

0.00

λprobe

= 487 nm

τS = 0.9 ps (70 %)

16.3 ps (30 %)

Δ O

D

Time (ps)

Δ O

D

Wavelength (nm)

Time (ps) -2 1 1.2 1.5 2 3 4

5 6 7 8 9 10 13 15 20 25

a)

b)

Fig. S9 Femtosecond transient absorption spectra and decay profile (inset) of PBI 4 in a) chloroform

and b) methylcyclohexane.


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300 400 500 6000

10

20

30

40

ε (1

03 L

mo

l-1 c

m-1)

Wavelength (nm)

PBI 1 PBI 4

Fig. S10 Comparison of steady-state absorption spectra of PBI 1 (black, 1.3x10-4 M), and PBI 4 (red,

1.3x10-4 M) in methylcyclohexane.


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b)

a)

0.000005 0.000010 0.0000150.5

1.0

1.5

2.0

2.5

3.0

3.5

F0/F = 1 + 1.25x105 [PBI 4]

F0/F

[PBI 4] (mol/L)

0 5 10 15 20 25 300.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Inte

nsi

ty (

No

rm.)

PBI 4 / PBI 1 (%)

519 nm 560 nm 675 nm integrated spectra

500 600 700 800

560 nm

519 nm

PBI 4 (%) 1.4 2.5 3.9 5.0 6.4 7.7 8.910.111.312.613.614.815.916.917.919.020.822.624.326.528.430.332.0

Inte

nsi

ty (

a.u

.)

Wavelength (nm)

675 nm

c)

Fig. S11 Fluorescence a) spectral and its b) peak intensity change and c) Strem-Volmer plot for the

hetero-aggregates PBI. Ratio PBI 4 / PBI 1 is controlled.


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0 500 1000 1500 2000-0.50

-0.45

-0.40

-0.35

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

0.05λ

probe = 530 nm

Δ O

D

Time (ps)

510 pump 530 pump 550 pump

a)

b)

0 500 1000 1500 2000

0.00

0.05

0.10

0.15

0.20

0.25

Δ O

D

Time (ps)

510 pump 530 pump 550 pump

λprobe

= 830 nm

Fig. S12 Femtosecond transient decay profiles of PBI 1 (10-3 M) with various excitation wavelengths

(510, 530 and 550 nm) in methylcyclohexane .


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