N

N

O

O

S

S

S

S

0 50 100 150 200 250 300

Ex

oth

erm

ic

Temperature (C)

C6PT1C6

C6PT2C6

C6PT3C6

EHPT2C6

C6PT2

Single Crystal Structure and Film X-ray Diffraction

Abstract

Intermolecular Packing and Intramolecular Conformation

Optical Absorption and Solubility

Structural variation has remarkable effects on the materials’ fundamental

properties including molecular packing, thermal transitions, crystallinity,

optical absorption, energy levels, film morphology, and hole mobility.

Single crystal structures of these DPP-based compounds were compared

in terms of molecular packing style, intermolecular overlapping (areas and

distance), and intramolecular conformation.

Differences in material properties are found to arise from changes in intra-

and intermolecular interactions in the solid state caused by the structural

variations.

This study demonstrates a systematic investigation of structure-property

relationships in conjugated small molecules.

Film Morphology and Diode Mobility

Acknowledgments: This work is supported by the NSF-CAREER/SPECIAL CREATIVITY AWARD and NSF-

SOLAR. C. K. thanks the Department of Energy, Office of Basic Research for financial support. T.-Q.N thanks the Camille Dreyfus Teacher Scholar Award and the Alfred Sloan Fellowship.

Summary

References

Liu, J.; Kim, C.; Lin, J.; Tamayo, A.; Walker, B.; Wu, G.; Nguyen, T. -Q. Chemistry of Materials 2012, 24, 1699.

Influence of Structural Variation on Solid-State Properties of

Diketopyrrolopyrrole-Based Oligophenylenethiophenes

Jianhua Liu, Chunki Kim, Jason Lin and Thuc-Quyen Nguyen

Center for Polymers and Organic Solids and Department of Chemistry & Biochemistry, University of California, Santa Barbara, California, 93106 USA

Five compounds, based on diketopyrrolopyrrole (DPP) and phenylene

thiophene (PT) moieties, are synthesized to investigate the effect of structural

variations on material’s solid state properties. The structural variations are

focused on (a) backbone length by changing the number of thiophenes on both

sides of DPP, (b) alkyl substitution (n-hexyl or ethylhexyl) on DPP, and (c) the

presence of n-hexyl group at the end of the molecular backbone.

10 20 302 °

C6PT1C6 EHPT2C6

C6PT2C6 C6PT2

C6PT3C6a

b

c

d

e

fg

h

ij

NameIntermolecular backbone

overlappinga

Interplane

distanceb (Å)

C6PT1C6 3.28

C6PT2C6 3.26

C6PT3C6 3.37

EHPT3C6 3.27c

C6PT2 3.23

Name φ1 (o) φ2 (

o)

C6PT1C6 26.2 22.8

C6PT2C6 23.7 10.2

C6PT3C6 25.1 16.5

EHPT2C6 37.6 17.4

C6PT2 26.2 14.2

N

N

O

O

R1

R1

S

S

R2

R2

φ1

φ2

a

b

c

(a) (b) (c)

(d)

(f)

(e)

300 400 500 600

0.0

0.2

0.4

0.6

0.8

1.0

Ab

so

rba

nc

e (

a.u

.)

Wavelength (nm)300 400 500 600 700

0.0

0.2

0.4

0.6

0.8

1.0 C6PT1C6

C6PT2C6

C6PT3C6

EHPT2C6

C6PT2

Ab

so

rba

nc

e (

a.u

.)

Wavelength (nm)

(a) (b)

-5.16

-3.32

C6PT2C6

-5.63

-3.66

C6PT1C6

-5.24

-3.38

C6PT3C6

-5.49

-3.51

EHPT2C6

-5.37

-3.43

C6PT2

EA

IP

Egopt

Egopt

1.97

1.84 1.86

1.981.94

-5.16

-3.32

C6PT2C6

-5.63

-3.66

C6PT1C6

-5.24

-3.38

C6PT3C6

-5.49

-3.51

EHPT2C6

-5.37

-3.52

C6PT2

LUMO

HOMO

Egopt

Egopt

1.97

1.84 1.861.98 1.85

40 80

10-6

10-5

EHPT2C6

C6PT2

C6PT1C6

C6PT2C6

C6PT3C6

Ho

le m

ob

ilit

y (

cm

2/V

s)

Temperature (C)

Name

Solution Film Tm

(ºC)

Tc

(ºC)

Solubility

(mg/mL) λmax

(nm)

λonset

(nm)

Eg (opt)

(eV)

ɛ

(M-1cm-1)

λmax

(nm)

λonset

(nm)

Eg (opt)

(eV)

HOMO

(eV)

LUMO

(eV)

C6PT1C6 505 571 2.17 3.2104 582 629 1.97 -5.63 -3.66 181 143 228

C6PT2C6 521 591 2.09 4.6104 614 674 1.84 -5.16 -3.32 231 194 11

C6PT3C6 528 602 2.06 5.6104 608 667 1.86 -5.24 -3.38 263 229 1.5

EHPT2C6 514 584 2.12 4.8104 532 626 1.98 -5.49 -3.51 164 77 53

C6PT2 516 587 2.11 4.4104 554 671 1.85 -5.37 -3.52 249 184 6.3

C6PT1C6, C6PT2C6, C6PT3C6, and C6PT2

(a-c) Vs. EHPT2C6 (d-f). Unit cells viewed

from side (a, d), a axis (b), c axis (c, f), and b

axis (e).

Experimental measured patterns

(a, c, e, g, and i) Vs. Theoretical

patterns (b, d, f, h, and j)

aViewed orthogonal to the molecular long axis with red

rectangles highlighting the overlapping area. bThe interplanar

distance is calculated from phenyl-phenyl rings. cCalculated

from overlapped DPP rings.

Intermolecular Overlapping Area and Distance

DSC thermograms (10 oC/min)

Summary of Optical and Thermal Properties

Solution state

Ionization potential (IP) and electron

affinity (EA)

AFM height images of as-cast (top)

and annealed (bottom) films.

Annealing condition: 100 ºC for 10

min. Scan size: 2 µm 2 µm.

Hole mobility of as-cast (25 ºC)

and thermal annealing (80 ºC

and 100 ºC) films.

Name φ1 (o) φ2 (

o)

C6PT1C6 26.2 22.8

C6PT2C6 23.7 10.2

C6PT3C6 25.1 16.5

EHPT2C6 37.6 17.4

C6PT2 26.2 14.2

N

N

O

O

R1

R1

S

S

R2

R2

φ1

φ2

Conjugated Backbone Conformation

aφ1 (C-C-C-C) and φ2 (X-C-C-C) as

illustrated by the general molecular

structure at bottom.

C6PT1C6 C6PT2C6 C6PT3C6 EHPT2C6 C6PT2

IP determined by UPS and EA obtained by EA = Egopt - |IP|.

Thermal Property and Energy Level

Thin film XRD Two molecular packing motif observed

Absorption redshift saturates as increasing conjugate length.

Tm and solubility have opposite sequence.

Ethylhexyl substitution significantly affects solid state absorption.

Film state

N

N

O

O

SS

N

N

O

O

SSS

S

S

S

C6PT1C6 EHPT2C6

C6PT2C6

C6PT3C6 C6PT3C6

N

N

O

O

SSS

S

Conjugation length

Alkyl chain on DPP

End alkyl chain Conjugation length

N

N

O

O

S

S

S

S