Exciton-phonon (EP) coupling in molecular crystals is investigated in the case where two intramolecular vibrational modes are involved and a theoretical model is presented which applies when one of the modes is strongly coupled to crystal excitons. The model is used to simulate the low energy portion of the absorption spectra of quaterthiophene (4T) single crystals, for which we find it appropriate to consider a low energy vibrational mode at 161cm1 and an effective strongly coupled high energy mode at 1470cm1. Our numerical results demonstrate that the high energy mode renormalizes the excitonic band, thereby strongly affecting the environment seen by the low energy mode and the overall EP coupling regime. Numerical simulations also confirm the existence of the new coupling regimes “intermediate-I” and “strong-I” already introduced for oligothiophene aggregates [Spano et al, J. Chem. Phys.127, 184703 (2007)], which arise as a consequence of the large effective mass of low energy excitons in 4T crystals. Comparison with experimental high resolution absorption spectra is also reported and shown to support the model predictions.

1.
G.
Malliaras
and
R. H.
Friend
,
Phys. Today
58
,
53
(
2005
).
2.
J. H.
Burroughes
,
D. D. C.
Bradley
,
A. R.
Brown
,
R. N.
Marks
,
K.
Mackay
,
R. H.
Friend
,
P. L.
Burns
, and
A. B.
Holmes
,
Nature (London)
347
,
539
(
1990
).
3.
S. R.
Forrest
,
Nature (London)
428
,
911
(
2004
).
4.
H.
Sirringhaus
,
N.
Tessler
, and
R. H. R. H.
Friend
,
Science
280
,
1741
(
1998
).
5.
C. J.
Brabec
,
V.
Dyakonov
,
J.
Parisi
, and
N. S.
Sariciftci
,
Organic Photovoltaics: Concepts and Realization
(
Springer
,
New York
,
2003
).
6.
W. T.
Simpson
and
D. L.
Peterson
,
J. Chem. Phys.
26
,
588
(
1957
).
7.
E. G.
McRae
,
Aust. J. Chem.
14
,
329
(
1961
).
8.
E. G.
McRae
and
W.
Siebrand
,
J. Chem. Phys.
41
,
905
(
1964
).
9.
F. C.
Spano
,
L.
Silvestri
,
P.
Spearman
,
L.
Raimondo
, and
S.
Tavazzi
,
J. Chem. Phys.
127
,
184703
(
2007
).
10.
The simplified model aggregate of Ref. 9 consists of a square lattice with lattice constant d and one molecule per cell. This is equivalent to a square lattice with two molecules per cell and lattice constant a=d2, tilted by 45° with respect to the previous one. By unfolding the upper band in the second Brillouin zone, we can map the two band model into the single band model by simply rotating the wave vector space by 45°. Assuming isotropic parabolic bands Jk=Jcd2k2 in the simplified model is therefore equivalent to having the dispersion Jk=(Jc/2)a2k2 in the two band model, so that the maximum width of the lower band is Δ=Jcπ2.
11.
L.
Raimondo
,
M.
Laicini
,
P.
Spearman
,
S.
Tavazzi
, and
A.
Borghesi
,
J. Chem. Phys.
125
,
024702
(
2006
).
12.
T.
Siegrist
,
C.
Kloc
,
R. A.
Laudise
,
H. E.
Katz
, and
R. C.
Haddon
,
Adv. Mater.
10
,
379
(
1998
).
13.
W.
Gebauer
,
A.
Langner
,
M.
Schneider
,
M.
Sokolowski
, and
E.
Umbach
,
Phys. Rev. B
69
,
125420
(
2004
).
14.
X. H.
Sun
,
Z.
Zhao
,
F. C.
Spano
,
D.
Beljonne
,
J.
Cornil
,
Z.
Shuai
, and
J. -L.
Bredas
,
Adv. Mater.
15
,
818
(
2003
).
15.
D.
Fichou
,
G.
Horowitz
,
V.
Xu
, and
F.
Garnier
,
Synth. Met.
48
,
167
(
1992
).
16.
D.
Birnbaum
,
D.
Fichou
, and
B. E.
Kohler
,
J. Chem. Phys.
96
,
165
(
1992
).
17.
F.
Kouki
,
P.
Spearman
,
P.
Valet
,
G.
Horowitz
, and
F.
Garnier
,
J. Chem. Phys.
113
,
385
(
2000
).
18.
M.
Laicini
,
P.
Spearman
,
S.
Tavazzi
, and
A.
Borghesi
,
Phys. Rev. B
71
,
045212
(
2005
).
19.
S.
Tavazzi
,
M.
Campione
,
M.
Laicini
,
L.
Raimondo
,
A.
Borghesi
, and
P.
Spearman
,
J. Chem. Phys.
124
,
194710
(
2006
).
20.
S.
Tavazzi
,
A.
Borghesi
,
M.
Campione
,
M.
Laicini
,
S.
Trabattoni
, and
P.
Spearman
,
J. Chem. Phys.
120
,
7136
(
2004
).
21.
F.
Meinardi
,
M.
Cerminara
,
A.
Sassella
,
R.
Bonifacio
, and
R.
Tubino
,
Phys. Rev. Lett.
91
,
247401
(
2003
).
23.
M.
Muccini
,
M.
Schneider
,
C.
Taliani
,
M.
Sokolowski
,
E.
Umbach
,
D.
Beljonne
,
J.
Cornil
, and
J. L.
Bredas
,
Phys. Rev. B
62
,
6296
(
2000
).
24.
P. F.
van Hutten
,
J.
Wildeman
,
A.
Meetsma
, and
G.
Hadziioannou
,
J. Am. Chem. Soc.
121
,
5910
(
1999
).
25.
C. C.
Wu
,
M. C.
Delong
,
Z. V.
Vardeny
, and
J. P.
Ferraris
,
Synth. Met.
137
,
939
(
2003
).
26.
A. S.
Davydov
,
Theory of Exciton
(
Plenum
,
New York
,
1971
).
27.
P.
Petelenz
and
M.
Andrzejak
,
Chem. Phys. Lett.
343
,
139
(
2001
).
28.
P.
Petelenz
and
M.
Andrzejak
,
J. Chem. Phys.
113
,
11306
(
2000
).
29.
Z.
Zhao
and
F. C.
Spano
,
J. Phys. Chem. C
111
,
6113
(
2007
).
30.
T.
Holstein
,
Ann. Phys. (San Diego)
8
,
325
(
1959
).
31.
M. J.
Frisch
,
G. W.
Trucks
,
H. B.
Schlegel
 et al, GAUSSIAN03, Revision C.01, Gaussian, Inc., Wallingford, CT,
2004
.
32.
I.
Vragovic
and
R.
Scholz
,
Phys. Rev. B
68
,
155202
(
2003
).
33.
R.
Scholz
,
A.
Kobitski
,
T.
Kampen
,
M.
Schreiber
,
D.
Zahn
,
G.
Jungnickel
,
M.
Elstner
,
M.
Sternberg
, and
T.
Frauenheim
,
Phys. Rev. B
61
,
13659
(
2000
).
34.
M.
Andrzejak
and
M. T.
Pawlikowski
,
J. Phys. Chem. A
112
,
13737
(
2008
).
35.
Z.
Zhao
and
F. C.
Spano
,
J. Chem. Phys.
122
,
114701
(
2005
).
You do not currently have access to this content.