Comprehensive analysis of fragment orbital interactions to build highly π-conjugated thienylene-substituted phenylene oligomers

FULL PAPER

DOI: 10.1002/chem.201203869

Comprehensive Analysis of Fragment Orbital Interactions to Build Highly

p-Conjugated Thienylene-Substituted Phenylene Oligomers

Jean-Charles Florꢀs,^[a]Marie-Agnꢀs Lacour,^[a]Xavier Sallenave,^[a]

FranÅoise Serein-Spirau,*^[a]Jean-Pierre Lꢀre-Porte,^[a]Joꢁl J. E. Moreau,^[a]

Karinne Miqueu,^[b]Jean-Marc Sotiropoulos,^[b]and David Flot^[c]

Dedicated to Dr. G. Pfister-Guillouzo for her contribution to the study of the electronic properties of new systems by coupling

UV photoelectron spectroscopy and quantum chemistry

ꢀ

Abstract: p-Conjugated thienylene

phenylene oligomers with fluorinated

and dialkoxylated phenylene fragments

have been designed and prepared to

understand the interactions in fragment

orbitals, the influence of the substitu-

ents (F, OMe) on the HOMO–LUMO

gap, and the role of intramolecular

non-covalent cumulative interactions in

the construction of p-conjugated nano-

structures. Their strong conjugation

was also evidenced in the gas phase by

UV photoelectron spectroscopy and

theoretical calculations. These results

can be explained by the crucial role of

the relative energetic positions of the

p orbitals of the dimethoxyphenylene,

which was used to model the dialkoxy-

phenylene entity, in determining the p/

p^*orbital levels of the fluorinated phe-

nylene entity. Dialkoxyphenylenes

raise the HOMO orbitals, whereas flu-

orinated phenylenes lower the LUMO

orbitals in the oligomers. In addition,

the presence of S···F and H···F interac-

HOMO–LUMO gap (according to

DFT calculations) and by a relatively

strong maximum wavelength (as ob-

tained by TD-DFT calculations and ex-

perimental UV/Vis measurements).

The crystallographic data of two mixed

ꢀ

tions in the fluorinated phenylene

ꢀ

thienylene compounds add to the S···O

interactions in the mixed targets and

contribute to the full conjugation in the

oligomer, inducing weak inter-ring

angles between the involved aromatic

cycles. These results, which showed ex-

tended conjugation of the p system,

thienylene (fluorinated and dialkoxy-

lated phenylene) five-ring oligomers

agree with the above results and show

the formation of quasi-planar confor-

mations with non-covalent S···O, H···F,

and S···F interactions. These studies in

the solid and gas phases show the rele-

vance of associating dialkoxyphenylene

and fluorinated phenylene fragments

with thiophene to lead to oligomers

with improved electronic delocalization

for electronic or optoelectronic devices.

were corroborated by

a

narrow

Keywords: density functional calcu-

lations · heterocycles · nanostruc-

tures · noncovalent interactions ·

oligomers

Introduction

p-Conjugated organic oligomers and polymers have received

much attention over the last few years because of their po-

tential applications in the field of plastic electronics.^[1]Their

remarkable electronic and electro-optical properties are

easy to tune, owing to the molecular and supramolecular

chemistry extended resources. Regioregular poly(3-alkyl-

[a] Dr. J.-C. Florꢀs, Dr. M.-A. Lacour, Dr. X. Sallenave,

Prof. F. Serein-Spirau, Prof. J.-P. Lꢀre-Porte, Prof. J. J. E. Moreau

Institut Charles Gerhardt, UMR 5253 CNRS

Equipe AM₂N, Ecole Nationale Supꢁrieure de Chimie de

Montpellier, 8, rue de lꢂEcole Normale

34296 Montpellier Cedex 05 (France)

E-mail: francoise.spirau@enscm.fr

ACHUTNGERNtNUG hioHCATUNGTRENNpUGN henes) are the most notable class of p-conjugated ma-

[b] Dr. K. Miqueu, Dr. J.-M. Sotiropoulos

Institut des Sciences Analytiques et de

terials because they exhibit excellent chain planarity and ex-

tended conjugation lengths, owing to their head-to-tail re-

giochemistry, thus leading, in some cases, to highly conjugat-

ed sheets with high field-effect mobilities.^[2,3]More recently,

highly regioregular thienylene-2,5-dialkoxyphenylene co-

polymers have been recognized for their high conjugation

over the p system along their backbone, owing to the pres-

ence of polar dialkoxy chains, which are favorable for high-

quality homogeneous thin-film coatings on glass with very

low band-gaps and low oxidation potentials.^[4]Ordering of

the polymer chains can result from coating them onto an

Physico-Chimie pour lꢂEnvironnement et les Matꢁriaux

IPREM UMR CNRS 5254, Equipe Chimie-Physique

Universitꢁ de Pau et des Pays de lꢂAdour

Hꢁlioparc, 2 Avenue du Prꢁsident Angot

64053 Pau Cedex 09 (France)

[c] Dr. D. Flot

Structural Biology Group

ESRF, B.P. 220, 6, rue Jules Horowitz

38043 Grenoble Cedex (France)

Supporting information for this article is available on the WWW

under http://dx.doi.org/10.1002/chem.201203869.

Chem. Eur. J. 2013, 00, 0 – 0

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oriented Teflon deposit to achieve polarized fluorescence^[5]

or from the self-organization of macromolecular chains into

lamellar structures, which can be tuned by privileged p-

and their recently evidenced involvement in the supramolec-

ular organization of oligomers,^[8]alkoxy chains have been

demonstrated to reinforce the extended conjugation proper-

ties of the conjugated sequence because they induce intra-

molecular noncovalent sulfur···oxygen interactions that orig-

inate from self-rigidification of the conjugated segments into

quasi-planar conformations.^[9]

stacking interactions.^[4]Oligo(phenylene thienylenes) have

ꢀ

been revealed to be good transport materials because inter-

esting mobilities can be achieved in organic field-effect tran-

sistors with these stable and easily processable com-

pounds.^[6,7]To overcome the solubility problems that arise

The phenylene substituent has a clear impact on the con-

ꢀ

for chains of longer than five or six oligo(phenylene thien-

jugation in regioregular alternating thienylene phenylene

yl

R

sequences. Therefore, fundamental investigations are re-

quired: 1) to improve and better tune the optoelectronic

properties of both these sequences and their isolated frag-

ments to optimize their conjugation and 2) to better under-

stand and tune their chemical behavior, both at the molecu-

lar level and from a supramolecular point of view. It seems

particularly important to identify better frameworks, with

suitable substituents on the benzene rings, that lead to ap-

propriate HOMO and/or LUMO orbital levels with a weak

of their extended conjugation, alkyl and especially alkoxy

chains were introduced onto the conjugated backbone,

thereby leading to a class of (2’-thienylene-2,5-dialkoxy-

ACHTUNGTRENNUNGphenACHTUNGTRENNUNGylene) oligomers. Indeed, beyond their solubilizing role

Abstract in French: Des oligomꢀres thiꢁnylꢀne-phꢁnylꢀne ont

ꢁtꢁ conÅus et prꢁparꢁs en incorporant dans lꢂenchaꢃnement

des motifs fluoro- et dialkoxyphꢁnyles afin de comprendre

lꢂinteraction des orbitales molꢁculaires entre les fragments,

lꢂinfluence des substituants (F, OMe) sur lꢂꢁcart HOMO–

LUMO et le rꢄle dꢂinteractions intramolꢁculaires cumulꢁes

non-covalentes afin dꢂꢁlaborer des nanostructures fortement

p-conjuguꢁes. Leur forte conjugaison rꢁsultante a ꢁgalement

pu Þtre mise en ꢁvidence, en phase gazeuse, grꢅce ꢆ la con-

frontation des rꢁsultats de la spectroscopie photoꢁlectronique

ꢆ rayonnement UV et des calculs thꢁoriques. Celle-ci peut

sꢂexpliquer par le rꢄle crucial de la position ꢁnergꢁtique rela-

tive des orbitales p du dimꢁthoxyphꢁnylꢀne, pris comme

modꢀle du motif dialkoxyphꢁnylꢀne, par rapport ꢆ celle des

orbitales p/p^*des entitꢁs fluorobenzꢀne. Les sous-unitꢁs dial-

koxyphꢁnylꢀne contribuent ꢆ ꢁlever le niveau de la plus haute

orbitale occupꢁe (HO) tandis que les fragments fluoroben-

ꢀ

HOMO–LUMO gap and high inter-ring p p interactions,

which are a confirmation of strong conjugation in these

oligomers. Two factors can affect this conjugation in differ-

ent ways: 1) the energetic positions of the involved frag-

ments in the sequence (Figure 1), and 2) the orbital overlap

between the motifs, which can be improved by narrowing

the dihedral angle between the different units, owing to the

presence of specific interactions.

Hence, a joint experimental and theoretical approach

could provide further insight into this conjugation. On the

one hand, the HOMO–LUMO gap and the absorption max-

imum wavelength can be estimated theoretically by using

DFT and TD-DFT calculations, respectively, and experimen-

tally by using UV/Vis absorption spectroscopy. On the other

hand, evaluation of the inter-ring p p interactions (DE )

can be provided by UV photoelectron spectroscopy

(Figure 2). Moreover, the coupling of photoelectron spec-

ACHUTNGERNtNUG rosAHCTUNGTRENNcUGN opy with theoretical calculations allows the determina-

p

ꢀ

ACHTUNGTRENNUNGzꢀne diminuent le niveau ꢁnergꢁtique de la plus basse orbitale

vacante (BV) des oligomꢀres. De plus, la prꢁsence des inter-

actions S···F et H···F dans les oligomꢀres thiꢁnylꢀne-fluoro-

phenylꢀne ajoutꢁe ꢆ la prꢁsence de lꢂinteraction S···O dans les

nanostructures mixtes possꢁdant des phenylꢀnes fluorꢁs et

dialkoxylꢁs contribuent ꢆ une conjugaison totale et induisent

la diminution de lꢂangle de torsion entre les cycles aromat-

tion of the nature and the energetic position of the molecu-

lar orbitals.

In a previous report,^[9]the construction of highly conjugat-

ed oligomers that contained thienylene and 2,5-dialkoxy-

ACHUTNGERNpNUG henHCATUNGTRNEyNUGN lene moieties through a combined experimental and

ACHTUNGTRENNUNGiques impliquꢁs. Ces rꢁsultats dꢁmontrant une conjugaison

theoretical (DFT) approach was described. Even though

this sequence was found to be relevant to the synthesis of

fully conjugated oligomeric systems, new families of thieny-

lene and substituted-phenylene fragments were investigated

to achieve much narrower HOMO–LUMO band-gaps,

which would be more appropriate for applications in organic

electronics. Thus, for this purpose, the design of oligomers

that contain moieties that lower the LUMO level of the con-

ꢁtendue du systꢀme p ont ꢁtꢁ corroborꢁs par un faible ꢁcart

ꢁnergꢁtique HOMO–LUMO mis en ꢁvidence par les calculs

de DFT ainsi quꢂune longueur dꢂonde maximale relativement

importante obtenue par des calculs de TD-DFT et des mesu-

res expꢁrimentales en spectroscopie UV/Vis. Les donnꢁes cris-

tallographiques obtenues sur deux oligomꢀres ꢆ cinq cycles

thiꢁnylꢀne-(fluoro- et dialkoxyphꢁnylꢀne) corrꢀlent les rꢁsul-

tats prꢁcꢁdents et mettent en ꢁvidence des conformations

quasi-planes avec des interactions non-covalentes S···O, H···F

et S···F. Ces ꢁtudes rꢁalisꢁes ꢆ la fois ꢆ lꢂꢁtat solide et en phase

gazeuse montrent bien la pertinence dꢂassocier des fragments

dialkoxyphꢁnylꢀne et fluorophꢁnylꢀne ꢆ du thiophꢀne pour

conduire ꢆ des oligomꢀres prꢁsentant une trꢀs forte dꢁlocali-

sation ꢁlectronique, pouvant Þtre utilisꢁs dans des dispositifs

dꢂꢁlectronique ou dꢂopto-ꢁlectronique.

ꢀ

jugated chain should be considered, because a thienylene

dialkoxy

G

E

G

very wide range of electron-withdrawing groups, such as

acyl cyanomethylene,^[10]tetracyanobutadiene,^[11]dicyanovin-

yl,^[12]trifluoromethylphenyl^[13]or pentafluorophenyl moiet-

ies,^[14,15]have been introduced into oligothiophene chains

and they have contributed to dramatically lowering the

LUMO level of the resulting organic materials, thus opening

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Highly p-Conjugated Thienylene-Substituted Phenylene Oligomers

FULL PAPER

torsion angles.^[19,20]These quasi-

planar conformations, as evi-

denced by X-ray crystallogra-

phy, which favor extended con-

ꢀ

jugation of the thienylene

phen

A

G

result from the packing effects

in the crystal state. To develop

low-band-gap systems to ach-

ieve fully p-conjugated oligo-

AHCTUNGTRENGNmUN ers, the strong attractive elec-

tronic effect of fluorine atoms,

which are associated to its abili-

ty to generate intramolecular

noncovalent S···F and H···F in-

teractions, encouraged us to

design and investigate a new

family of p-conjugated thienACHTUNGTRENNUNGyl-

ꢀ

ene phen

employ polyfluorinated ben-

zene moieties.

E

G

Herein, the fluorinated phen-

AHCTUNGTERGyNNUN lene moieties impact to affect

the intrinsic conjugation of thi-

ꢀ

G

was investigated. Thus, small

systems with two or three aro-

matic units (thienylene-fluori-

nated phenylene or bisthien-

Figure 1. Nature and energetic positions of the occupied and virtual molecular orbitals of various fragments

that are involved in the conjugation, calculated at the B3LYP/6-31G** level of theory.

ylene-fluorinated

phenylene)

have been first studied before

more extended conjugated sys-

tems, by joint experimental and

theoretical approaches.

up their application as efficient organic solar cells or as elec-

tron-transporting OFETs with high mobility. Among the

various contributors to narrowing the band-gap and decreas-

ꢀ

ing the LUMO level in thienylene phenylene sequences,

Results and Discussion

the use of halogen atoms for backbone functionalization

plays a crucial role and, in particular, fluorination has a dra-

matic effect, because it improves the electron-accepting abil-

ity, lowers the electron-injection barrier, and favors face-to-

face stacking (rather than edge-to-face stacking) of the con-

jugated systems.^[15–17]Beyond the role of fluorine atoms in

influencing the charge-transporting semi-conductive proper-

ties of the conjugated system through its electronic effects

and preference for face-to-face stacking, nonbonding chalco-

gen···halogen interactions and, in particular, sulfur···fluorine

(S···F) or hydrogen···fluorine (H···F) interactions, have been

reported as a driving force for the self-rigidification of the

Among all of the compounds that were in this study, only a

few of them were prepared for their novelty or as model

compounds for the gas-phase experimental photoelectron

spectroscopy measurements (Scheme 1). More precisely, 2-

(1,4-difluorophenyl)thiophene (BTF₂), 2,5-bis(pentafluoro-

phenyl)thiophene (BTBF), and 2,5-bis(1,4-dimethoxy

ACHTUNGTRENNUNGphen-

AHCTUNGTREGUNyNN l)thiophene (BTBOMe) were employed as model com-

pounds that were only employed in the theoretical calcula-

tions. The synthesis of model compounds phenylthiophene

(BT), 2,(2,5-dimethoxyphenyl)thiophene (BTOMe), 1,4-

bis(2-thienyl)benzene (TBT), and 1,4-dimethoxy-2,5-bis(2-

thienyl)benzene (TBTOMe) has previously been reported

and their characterization data^[9]were obtained from a suc-

cessful comparison of their experimental UV photoelectron

spectra on gaseous samples and DFT theoretical calcula-

tions.

thienACHTUNGTRENNUNGylACHTUNGTRENNUNGene-based p-conjugated segments towards privileged

conformations.^[18–20]In the case of fluorine atoms, noncova-

lent intramolecular S···F and H···F interactions have been

observed in the solid state by X-ray diffraction of monocrys-

tals of thienylene-fluorinated phenylene-conjugated oligo-

ACHTUNGTRENNUNGmers, thus leading to shorter distances than the sum of their

van der Waals radii between sulfur and fluorine atoms in

thiophene or polyfluorobenzene rings and to low inter-ring

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F. Serein-Spirau et al.

Study of two- or three-ring thie-

ꢀ

nylene (fluorinated or meth-

oxylated)phenylene oligomers

Synthesis: Three model com-

pounds that contained the thi-

ꢀ

N

nylene pattern (1–3) were syn-

thesized by using Stille palladi-

um(0)-catalyzed cross-coupling

reactions, as detailed in the Ex-

perimental Section. Compounds

2 and 3 were prepared accord-

ing to the synthetic procedure

described in Scheme 2, which

involved 0.5 molar equivalents

of the corresponding dibromi-

nated phenylene moiety rela-

tive to 2-tributylstannylthio-

phene (Scheme 2).

Geometrical parameters: First,

calculations were carried out

with the B3LYP hybrid func-

p

ꢀ

Figure 2. Left: representation of the p p interactions (DE ) in compound 1, with experimental ionization po-

tential (IP) energies [eV] and the corresponding experimental photoelectron spectrum for the main IPs. Right:

experimental and theoretical (in square parentheses) DE^pvalues [eV], where DE^pis the energy difference be-

tional and the 6-31GACTHUNRGTNE(NUG d,p) basis

set on compounds 1, 2, 3, and

BTF₂to determine their geo-

metrical parameters and to ex-

amine the influence of fluorine

atoms on their structural prop-

erties (Table 1).

ꢀ

tween the MOs that are involved in the p p interactions.

A comparison was performed

between the geometrical pa-

rameters of compounds BT,

BTOMe, TBT, and TBTOMe.

For BTF₂, two conformers exist

on the potential-energy surface

and are isoenergetic. The syn

isomer exhibits a fluorine atom

that is oriented towards the

sulfur atom, whereas, in the anti

conformer, the fluorine atom is

oriented towards one of the hy-

drogen atoms of the thiophene

group. The two rings are slight-

ly twisted, with an inter-ring

ꢀ

angle (F) of 15–188 and a C_Th

C_Phbond length of about

1.47 ꢄ, which lies in between a

single and double bond. More

interesting are the distances be-

tween the

S and F atoms

(2.782 ꢄ) and between the H

and F atoms (2.277 ꢄ) in BTF₂.

These distances are shorter

than the sum of their corre-

sponding van der Waals radii,

Scheme 1. Reference (letters acronyms) and studied compounds (numbered compounds).

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Highly p-Conjugated Thienylene-Substituted Phenylene Oligomers

FULL PAPER

158 when the fluorine atom is in front of a hydrogen atom

of the thienylene groups. These different conformations

show short H···F and S···F distances of 2.26 and 2.77 ꢄ, re-

spectively. As previously observed for BTF₂, intramolecular

and noncovalent H···F and S···F interactions seem to be of

comparable importance in the stabilization of such systems.

As previously described for compound 3, two isoenergetic

conformers (syn and anti) are found for compound 2 on its

potential-energy surface. The calculated geometry for the

anti isomer describes a system in which the H···F and S···F

distances are the shortest (2.726 and 2.168 ꢄ, respectively)

because of the noncovalent H···F and S···F interactions, lead-

ing to an almost-planar molecule with a very weak inter-ring

torsion angle of 1.48 in the gas phase.

Scheme 2. Synthesis of 1,4-bis(2-thienyl)polyfluorophenylenes 2 and 3.

Table 1. Calculated bond lengths [ꢄ] and dihedral bond angles [8] in BT,

BTOMe, BTF2, TBT, TBTOMe, BTBOMe, BTBF, compounds 1–4, 5’,

and 6’.

Thus, a comparison of the geometrical structure of the flu-

orinated compounds with those of BT and BTOMe^[9]shows

that the presence of fluorine atoms facilitates the construc-

tion of more-planar systems. Consequently, these systems

should present a better overlap between the orbitals of the

two thienylene and phenylene rings.

ꢀ

C_Ph=C_Th

H X

S X

F

BT

BTOMe

BTF2

1

TBT

TBTOMe

2

3

4

1.469

1.471

1.467

1.466

1.467

1.463

1.469

1.465

1.468

1.469

1.466

HH: 2.398

HH: 2.190

HH: 2.199

HF: 2.223

HH: 2.376

HH: 2.167/2.172

HF: 2.169

HH: 2.190

HF: 2.226

HH: 2.132

HH: 2.163

SH: 2.827

SO: 2.798

SF: 2.783

SF: 2.772

SH: 2.818

SO: 2.785

SF: 2.726

SF: 2.778

SO: 2.743

SO: 2.796

28.5

24.2

15.4

17.1

26.2

21.1

1.4

11.7

17.8

16.1

25.3

22.7

13.8

16.1

16.5

15.6

12.9

18.6

14.2

18.5

17.7

26.8

Electronic properties: The photoelectron (PE) spectra of

compounds 1, 2, and 3 have been recorded to determine

their energetic splitting (DE^p), which is an indicator of the

inter-ring conjugation and gives information on the energet-

ic position of the HOMO. Figures 2, Figure 3, and Figure 4

show the PE spectra of compounds 1, 2, and 3, respectively

(for full interpretation of the PE spectra, see the Supporting

Information, Figures S1–S3).

BTBOMe

BTBF

5’

HF: 2.204

HF: 2.220

HF: 2.245

HF: 2.225

SF: 2.747

SF: 2.759

SF: 2.776

SF: 2.7792

SO: 2.742

SO: 2.733

SO: 2.737/2.766

SF: 2.787

1.465

In the spectrum of compound 1, three well-resolved bands

appeared between 8.6 and 10.3 eV (Figure 2). The observed

experimental ionization potentials (IP) resulted from strong-

6’

1.465

HF: 2.236

AHCTUNGTREGeNNNU r or weaker interactions between the fragments within the

molecule. Thus, if we consider the thiophene (p^T₁^h=8.9 eV

p

and p^T₂^h(n_S)=9.2 eV)^[21]and pentafluorobenzene p orbitals

(p^Ph=band centered at 10.0 eV),^[22]the PE spectra can be

described by considering a simple interactions diagram

(Figure 2). In particular, the first and third bands correspond

to the ejection of electrons that are localized on the molecu-

lar orbital (MO) in-phase and out-of-phase combinations of

the p^P₁^hand p^T₁^horbitals. These “semi-empirical” assignments

were confirmed by DFT calculations. It is worth noting that

the experimental value of DE^p(1.7 eV) is in good agree-

ment with the theoretical result (1.8 eV). The experimental

value is slightly weaker than that of BTOMe (1.9 eV), which

would indicate a less-important interaction between the two

aromatic entities in compound 1; however, the narrower

inter-ring torsion angle for compound 1 (178), compared to

that recorded for BTOMe (248), signifies better orbital over-

lap between the thienylene and substituted-phenylene rings

in compound 1 versus BTOMe. Therefore, the energetic po-

sitions of the fragments appear to have a crucial importance

for optimal conjugation in the oligomeric backbone.

which are 3.2 and 3.0 ꢄ, respectively. In perfluorinated com-

pound 1, both the S···F and H···F distances are shorter

(2.772 and 2.223 ꢄ, respectively); the dihedral angle (F=

17.18) has an intermediate value between those of the two

rotamers of BTF₂. For these two systems, the presence of

such S···F and/or H···F intramolecular interactions seems to

be important, thereby favoring a narrowing of the dihedral

angle (15–188) between the two rings in comparison with

those in BTOMe and BT (24–288). Moreover, the H···F and

S···F interactions seem to play similar roles in the stabiliza-

tion because, for BTF₂, the two conformers are isoenergetic

on the potential-energy surface.

When the skeleton grows longer by the addition of one

thienylene moiety, three almost-energetically equivalent

conformers are found on the potential-energy surface of

compound 3. In the first conformer, the two sulfur atoms on

the thienylene rings are in a syn orientation and the inter-

ring angles are between 8 and 148. In the other two con-

formers, the two sulfur atoms of the thienylene rings are in

an anti orientation and the torsion inter-ring angle is 118

when the fluorine atom is in front of the sulfur atom and

When the fluorine atom at the 4-position of the perfluoro-

phenylene group is substituted by a thienylene ring, the con-

jugated chain becomes longer and compound 2 is obtained;

its PE spectrum displays a first broad band at 7.8 eV

Chem. Eur. J. 2013, 00, 0 – 0

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F. Serein-Spirau et al.

Figure 3. Top: photoelectron spectrum of compound 2 with the main ioni-

zation potentials, as well as experimental and theoretical (in square pa-

rentheses) DE^pvalues [eV], where DE^pis the energy difference between

Figure 4. Top: photoelectron spectrum of compound 3 with the main ioni-

zation potentials, as well as experimental and theoretical (in square pa-

rentheses) DE^pvalues [eV], where DE^pis the energy difference between

ꢀ

the MOs that are involved in the p p interactions. Bottom: plot of the

ꢀ

two orbitals that are involved in the p p interactions and their associated

theoretical ionization potentials [eV].

ꢀ

the MOs that are involved in the p p interactions. Bottom: plot of the

ꢀ

two orbitals that are involved in the p p interactions and their associated

theoretical ionization potentials [eV].

(Figure 3). The second band is centered at 9.2 eV and the

third small and broad band appears at 10.3 eV. The ioniza-

tion potentials, which arise from the removal of an electron

from the delocalized p orbitals over the three rings can be

assigned to the first and third bands, at 7.8 and 10.3 eV, re-

spectively. As expected, the lengthening of the chain in-

creases the p-electron delocalization. The experimental (and

theoretical) DE^pvalues, at about 2.5 [2.7] eV for compound

2, are higher than those of compound 1, which are about 1.7

[1.8] eV.

The PE spectrum of compound 3 shows three well-sepa-

rated bands at 7.9, 8.9, and 9.4 eV and a broad band at

10.5 eV (Figure 4). The first (7.9) and the fourth bands

(10.5) correspond to the ejection of electrons from the p or-

bitals that are delocalized over the three rings. The experi-

mental and theoretical DE^pvalues are in very good agree-

ment, at about 2.6 eV. These values are close to those of

compound 2 and higher than that of BTF₂, which was calcu-

lated to be 2 eV.

To confirm these conclusions from the UV photoelectron

spectroscopy studies, the HOMO–LUMO gaps were calcu-

lated for all of the compounds because it is of crucial impor-

tance for describing the electronic delocalization. Moreover,

the maximum absorption wavelength was determined by

UV/Vis spectroscopy and compared to TD-DFT calcula-

tions. The results show that the HOMO–LUMO gaps in

compound 1 and BTF₂remain weak in these systems and

are intermediate between those of the corresponding non-

substituted phenylene compound BT and dimethoxylated-

phenylene analog BTOMe, as previously observed for the

DE^psplittings (Table 2). This tendency is also found in the

UV/Vis absorption maxima (l_max) of the fluorinated com-

pounds, which are close to that of BT and smaller than that

of BTOMe. As expected, the lengthening of the conjugated

chain led to a narrowing of the HOMO–LUMO gap by

about 0.7 eV (to 0.8 eV), which is in agreement with better

delocalization. Compounds 2 and 3 appear to be more con-

jugated than TBT, but less than TBTOMe. The HOMO–

LUMO gap in these fluorinated compounds is about 3.8 eV,

compared to 4.0 and 3.7 eV in TBT and TBTOMe, respec-

tively.

All of these results show that the above-explored fluori-

nated models and parent compounds BT and TBT show sim-

ilar electronic properties. Nevertheless, according to their

recorded and calculated DE^pvalues, their conjugation re-

mains slightly weaker than that in dimethoxy analogues

BTOMe and TBTOMe.

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Highly p-Conjugated Thienylene-Substituted Phenylene Oligomers

FULL PAPER

Table 2. Experimental and theoretical TD-DFT maximum wavelengths

[nm] and p!p* electronic transitions [eV] for BT, BTOMe, BTF2, TBT,

TBTOMe, BTBOMe, BTBF, compounds 1–4, 5’, and 6’.^[a]

trates the different contributions of each unit to the result-

ing conjugation (Figure 5). The small HOMO–LUMO gap

in BTOMe is mainly due to the high HOMO level of

DE^p

exptl calcd

First IP

exptl

ꢀ5.23 eV;^[9]the HOMO is mainly localized on the di

ACHTUNGTRENNUNGmeth-

l_max

p!p*

DE

(H/L)

exptl calcd

transition

AHCTUNGTREGoNNNU xyphenylene moiety and its high energy level results from

BT

285 276.2^[b]4.49^[b]

260.3^[c]4.76^[c]

4.80

4.31

4.55

4.60

4.00

3.70

3.80

3.83

3.66

3.72

3.92

3.13

3.14

1.70

2.10

2.00

1.80

2.40

2.70

2.90

2.55

2.36

3.16

3.33

1.7

1.9

–

8.1

7.6

–

the energetically destabilized HOMO (p_b1) in the 1,4-di-

meth

oxyphenylene fragment (e_KS=ꢀ5.31 eV). In the per-

A

ACHTUNGTRENNUNG

BTOMe

BTF2

1

325 315.8^[b]3.93^[b]

283.2^[c]4.38^[c]

fluorinated fragment, its HOMO (p_b1) and the LUMO are

both more stabilized than those in the dimethoxyphenylene

entity, because of the s-withdrawing effect of the fluorine

atoms on the benzene ring. Thus, the interactions with the

thiophene moiety lead to a HOMO in the oligomer that is

mainly localized on the thiophene ring and, hence, is less en-

ergetically accessible than that in the dimethoxylated-phen-

290.1^[b]4.72^[b]

270.7^[c]4.58^[c]

281 282.4^[b]4.39^[b]

265.7^[c]4.66^[c]

1.7

2.4

2.7

2.5

2.6

2.7

–

8.6

7.7

7.3

7.8

7.9

7.6

–

TBT

315 328.6^[b]3.77^[b]

300.7^[c]4.12^[c]

TBTOMe 358 361.3^[b]3.43^[b]

325.9^[c]3.80^[c]

p1

KS

ꢀ

ylene thienylene analogue. The difference in the

E

2

309 339.3^[b]3.65^[b]

312.4^[c]3.97^[c]

344.9^[b]3.59^[b]

316.4^[c]3.91^[c]

345 371.7^[b]3.34^[b]

326.9^[c]3.79^[c]

366.9^[b]3.38^[b]

326.4^[c]3.80^[c]

335.8^[b]3.69^[b]

309.4^[c]4.01^[c]

435.7^[b]2.85^[b]

381.8^[c]3.25^[c]

433.4^[b]2.86^[b]

379.4^[c]3.27^[c]

HOMO level that is induced by the substitution of a meth-

p1

KS

A

=

3

KS

ꢀ6.18 eV) on the phenylene ring is around 0.95 eV. Consid-

ering the LUMO level, this substitution leads to a less-im-

portant energy difference of only 0.67 eV, from ꢀ0.81 eV for

a methoxy substituent to ꢀ1.58 eV for a fluorine group.

Consequently, the HOMO–LUMO gap is increased in the

fluorinated oligomers, in spite of the more-accessible

LUMO level, owing to the s-withdrawing effect of the fluo-

rine atoms. According to Figure 5, the lower conjugation in

compound 1, as revealed by a lower value of DE^p, despite

having a weak and favorable inter-ring angle, can been ex-

plained by a two-orbital-level interaction, whereas the high-

est value of DE^p, as observed for BTOMe, which is indica-

tive of enhanced conjugation despite the less-favorable tor-

sion angle, can be explained by a three-level interaction be-

tween the p₁orbital (HOMO) of the thiophene and the

4

BTBOMe

BTBF

–

5’

6’

–

[a] HOMO–LUMO (DEACTHNUTRGNEUNG(H/L)) gap and experimental and theoretical

DE^psplittings [eV] were calculated at the B3LYP/6-31G** level of

theory. The experimental HOMO level [eV] was determined by using

UV-PES analysis. [b] TD-DFT calculations were performed at the

B3LYP/6-31G** level of theory. [c] TD-DFT calculations were performed

at the B3LYP/6-31G**//BHandLYP/6-31G** level of theory.

p_b1

G

phenylene, instead of the two-level interaction that was ob-

It is noteworthy that these results, summarized in Table 2,

show that the theoretical and experimental data are in good

agreement with one another.

In spite of the small dihedral angle, which is probably fa-

vored by the additive H···F and/or S···F intramolecular inter-

actions, the presence of fluorine atoms does not seem to im-

prove the conjugation, in comparison with the methoxy

group, which induces both the highest DE^pvalue and the

served for compound 1.

Theoretical study of the S···O, S···F and H···F intramolecular

noncovalent interactions: The nature of the nonbonding in-

tramolecular S···O, S···F and H···F interactions, which im-

prove the planarity of these oligomers, has been investigated

by means of natural bond orbital (NBO) and atoms-in-mole-

cules (AIM) analyses. These formalisms are typically used

to study noncovalent interactions between atoms and to

specify their electrostatic or covalent character.^[23,24]These

analyses were performed on BTOMe, TBTOMe, BTF2, and

compounds 1, 2, and 3.

ꢀ

smallest HOMO–LUMO gap in the thienylene phenylene

conjugated oligomers.^[9]Thus, as previously observed for

TBTOMe, the energy levels of the fragment that participate

in the interactions seem to play a crucial role in the overall

electronic delocalization (Figure 1).

NBO analysis: The total natural charges on the above-stud-

ied compounds were determined by a natural population

analysis of the more stable conformers, which showed elec-

trostatic S···O, S···F or H···F interactions between positively

charged sulfur (+0.49) or hydrogen atoms (ꢁ+0.25) and

negatively charged fluorine (ꢀ0.3) or oxygen atoms (ꢀ0.53)

and corroborated the short calculated S···O, S···F, or H···F

distances in the corresponding compounds. Secondly, an or-

bital contribution that involved the oxygen or fluorine lone-

pairs by second-order perturbation theory analysis, accord-

Role of the energy levels of the fragment orbitals in the con-

jugation: Therefore, to understand this above-observed dif-

ference between the conjugation in the fluorinated and

methACHTUNGTRENNUNGoxylated oligomers, the energetic positions of the fron-

tier orbitals were analyzed, both in the constitutive isolated

fragments of the oligomers and in the targeted methoxylat-

ꢀ

ed- and polyfluorinated-phenylene thienylene oligomers.

An interactions diagram between the dimethoxybenzene

or pentafluorobenzene units and the thienylene unit illus-

Chem. Eur. J. 2013, 00, 0 – 0

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F. Serein-Spirau et al.

AIM analysis: Bond critical

points (BCP) were located be-

tween the sulfur atoms and the

oxygen or fluorine atoms, as

well as between the hydrogen

atoms and the oxygen or fluo-

rine atoms. The Supporting In-

formation, Table S2, summariz-

es all of these data. For all of

these compounds, the electron

densities and the Laplacian

values are of the same orders of

magnitude. The electron densi-

ty, 1(r), at each BCP varies

ꢀ3

from 0.016 and 0.020 ea_o

,

which is within the range of the

hydrogen bonds.^[26]Moreover,

the positive value of the Lapla-

cian suggests a dominant elec-

trostatic character, in agree-

ment with the NBO data.^[27]

Our results are comparable to

those that were reported by

Tomoda and co-workers for

compounds that contained non-

bonding Se···O interactions.^[24]

In summary, in oligo(thienACHTUNGTRENNUNGyl-

ꢀ

G

enes), H···F and S···F intramo-

lecular noncovalent interactions

lead to quasi-planar geometries.

The electronic effects of the

phenylene

substituents

(F,

OMe) on the HOMO and

LUMO levels and on the conju-

gation (DE^p) for the two- and

three-ring model compounds

are shown in Figure 6.

The s-withdrawing effect of

the fluorine atoms influences

the energetic positions of the

molecular orbitals. The LUMO

becomes lower in energy by

Figure 5. Representation of the interactions between the phenylene and thienylene rings in compounds 1 and

BTOMe, as well as their corresponding Kohn–Sham energies (e_KS, in eV).

ing to NBO calculations, was also performed. The calculated

stabilizing energies reveal that the interactions between the

two correctly directed lone pairs (n_Oor n_F) and the s*_CꢀS

comparison with the other systems. At the same time, the

HOMO is also highly stabilized, more so than the LUMO.

[25]

ꢀ

The thienylene fluorophenylene sequences are interesting

orbitals in these noncovalent intramolecular interactions are

weak and that this contribution increases slightly when the

conjugated chain is extended further (see the Supporting In-

formation, Table S1). For BTF₂and compound 1, the n_F!

s*_CSstabilizing interaction has the same magnitude as the

n_O!s*_CSinteraction in BTOMe (about 2 kcalmol^ꢀ1). For

compounds 3 and 2, two n_F!s*_CSinteractions also exist,

each of which are about 2.2 and 2.6 kcalmol^ꢀ1, respectively

(Sn_F!s*_CꢀS=4.4 kcalmol^ꢀ1for compound 3 and Sn_F!

s*_CꢀS=5.2 kcalmol^ꢀ1for compound 2).

because they are quasi-planar and have a very accessible

LUMO level. Nevertheless, they are slightly less conjugated

than their dimethoxyphenylene analogues, which are charac-

terized by a high-energy HOMO level (Table 2). Conse-

quently, the use of polyfluorophen

ACTHUNGTRNENUNG AHCUNTGERNeNUG ne and dimethoxyphe-

nylene fragments in the same oligoAHCUTNGTRENNUNG

for improving the conjugation and narrowing the HOMO–

LUMO gap. New structures could combine the low LUMO

ꢀ

level of the thienylene fluoro

high HOMO level of thienylene-1,4-dimethoxyphenylene se-

quences. For this purpose, mixed 1,4-dimethoxy- and poly-

ACHTUNGTRENpUNGN henACHTUNRTGEGyNNNU lACHTNUGTRENeNNGU ne sequences and the

A

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Highly p-Conjugated Thienylene-Substituted Phenylene Oligomers

FULL PAPER

adopts a quasi-planar confor-

mation. The computed dihedral

angles between the phenylene

and thiACTHNUTRGENNGeU nCAHUTNGTRENyNUGN lene fragments are

within the range 16–188. NBO

analysis shows that the stabiliz-

ing interactions involve one of

the fluorine or oxygen lone

pairs and that the s*_CꢀSorbitals

are close to the previously ob-

served values for the perfluori-

nated compounds. Moreover,

the AIM analysis was similar to

those of the three-ring phen-

ꢀ

A

molecules.

Figure 7 shows the photoelec-

tron spectrum of compound 4,

which reveals an experimental

DE^psplitting of 2.7 eV (calcd:

2.9 eV) and a first ionization

potential (at 7.6 eV) that is as-

sociated to the HOMO level.

The calculated HOMO–LUMO

Figure 6. Effect of the phenylene substituent on the orbitals levels of the: a) two-, and b) three-ring thien-

ꢀ

A

fluorinated-phenylene moieties were associated in the same

ꢀ

p-conjugated thienylene phen

tronic properties were determined.

G

Study of longer mixed-fluorinated-and-methoxylated-phen-

ꢀ

G

oligomers were prepared and studied by using a combined

approach of UV photoelectron spectroscopy (UV-PES) in

the gas phase and density functional theory (DFT) calcula-

tions.

Study of a three-ring compound: Compound 4 was prepared

in a stepwise manner through palladium(0)-catalyzed Stille

cross-coupling reactions between roughly equimolar

amounts of 2-(2,5-dimethoxyphenyl)-5-tributylstannylthio-

phene and pentafluorobromobenzene (Scheme 3).

Scheme 3. Synthesis of 2-(2,5-dimethoxyphenyl)-5-(perfluorophenyl)thio-

phene (4).

BTOMe was prepared according to a literature proce-

dure.^[9]Selective monolithiation at the a position of the

sulfur atom on the thiophene moiety was performed by the

reaction of one equivalent of 2-(2,5-dimethoxyphenyl)thio-

phene with one equivalent of butyl lithium at ꢀ508C in an-

hydrous THF and the monolithiated intermediate was

quenched with one equivalent of tributylstannylchloride.

After treatment and ¹H NMR analysis, the crude tributyl-

stannyl intermediate (7) was used directly without further

purification in a subsequent palladium(0)-catalyzed cross-

coupling reaction with pentafluorobromobenzene. Thus,

compound 4 was isolated in 43% yield after purification.

Two rotamers of compound 4 exist on its potential-energy

surface. The global minimum locates the sulfur atom in con-

tact with the oxygen atom, with the shortest distance in this

series of compounds (2.743 ꢄ, Table 1). The molecule

gap is 3.7 eV, which is in good agreement with the experi-

mental optical value (3.6 eV).

The geometric and electronic data of compound 4 can be

compared to those of the corresponding methoxylated

(TBTOMe and BTBOMe) and fluorinated compounds (2

and BTBF; Table 1, Table 2, Figure 7) to appreciate the use

of mixed fluorinated and methoxylated oligomers. Com-

pared to the other compounds, compound 4 adopts a quasi-

planar structure and has a low HOMO–LUMO gap and a

high DE^pvalue, in agreement with good intramolecular

p conjugation. The HOMO–LUMO gap is comparable to

those in the methoxy compounds (TBTOMe and

BTBOMe). Moreover, compound 4 has a lower HOMO

level, which can improve the stability of the material and

would contribute to enhance the open-circuit voltage

Chem. Eur. J. 2013, 00, 0 – 0

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F. Serein-Spirau et al.

Study of two five-ring compounds: The second type of p-

ꢀ

conjugated thienylene phenylene oligomers that contain

methoxy and polyfluorinated phenylene moieties in the

same structure are constituted from two five-aromatic-ring

models (5 and 6), which are longer than oligomers 1–4 and

in which the conjugation should be more extended. More-

over, the substructure of compound 4 is included in com-

pounds 5 and 6, the only difference is the octoxy substitu-

ents, which are introduced instead of the methoxy groups to

ensure good solubility of compounds 5 and 6 (Scheme 1).

Compounds 5 and 6 were designed in this way to benefit

from cumulative intramolecular noncovalent interactions be-

tween the sulfur atoms and the oxygen or fluorine atoms

and between the hydrogen and fluorine atoms to achieve

more-planarized and, hence, more-conjugated entirely de-

fined nanostructures. As in other relevant highly conjugated

ꢀ

oligo(thienylene polyfluorophenylene)s, which are self-rig-

A

venient as p-type organic semi-conductors,^[19]the pentafluo-

rophenylene or phenylene end-capping groups confer better

A

stability on compounds 5 and 6, in particular towards oxida-

tion, and prevent the thiophene core from undergoing any

uncontrolled oxidative coupling.

Synthesis: Palladium(0)-catalyzed Stille cross-coupling reac-

tions between bromopentafluorobenzene and 2-tributylstan-

nylthiophene allowed the synthesis of 2-(pentafluoro

ACHTUNGTRENNUNGphen-

AHCTUNGTREGyNNUN l)thiophene (1) in 65% yield, which was stannylated to

afford 2-(pentafluorophenyl)-5-tributylstannylthiophene (8)

in 95% yield by a selective a-sulfur-lithiation/tributylstan-

Figure 7. Top: photoelectron spectrum of compound 4 with the main ioni-

zation potentials, as well as experimental and theoretical (in square pa-

rentheses) DE^pvalues [eV], where DE^pis the energy difference between

ꢀ

the MOs that are involved in the p p interactions. Bottom: plot of the

A

ACHTUNGTRENaNUGN tion sequence. Two equivalents of this latter compound

ꢀ

two orbitals that are involved in the p p interactions and their associated

theoretical ionization potentials [eV].

A

ACHTUNGTRENNUNG

coupling reaction, which led to compound 5 in 40% yield

(VOC) of an organic solar cell if compound 4 were used as

the p-donor material.

after purification (Scheme 4a).

ꢀ

Scheme 4. Synthesis of symmetric (5) and unsymmetric fluorinated and dialkoxylated phenylene thienylene oligomers (6).

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Highly p-Conjugated Thienylene-Substituted Phenylene Oligomers

FULL PAPER

The preparation of unsymmetric compound 6 was realized

in two main steps from two intermediate substructures. The

first compound, 5-tributylstannyl-2-phenylthiophene (14),

was prepared in 96% yield in a roughly analogous manner

to compound 8 through a selective a-sulfur-lithiation/tribu-

tylstannylation sequence from phenylthiophene.^[9]The

second substructure (6) was synthesized in a three-step

chemical route. Compound 11 was obtained by the double

O-alkylation of bromohydroquinone with 1-bromooctane in

77% yield and was selectively iodinated at the para position

to the bromine atom^[28]to give unsymmetrical dihalogenated

phenylene moiety 12 in 90% yield. Then, compounds 8 and

12 were reacted together in a 1:1 molar ratio in a palladi-

um(0) catalyzed Stille cross-coupling reaction to afford com-

pound 6 in 38% yield after purification (Scheme 4b).

Geometrical parameters: As expected, the lengthening of

the conjugated backbone contributes to the improved elec-

tronic properties of these systems. Calculations on model

compounds 5’ and 6’, which are the methoxylated analogues

of compounds 5 and 6, respectively, reveal weak inter-ring

angles (from 14 to 278) and support the presence of three

noncovalent S···O, S···F, and H···F interactions because these

distances (2.7, 2.8, and 2.2 ꢄ, respectively) are smaller than

the sum of their Van der Waals radii (3.32, 3.27, and 2.56, re-

spectively). In compounds 5’ and 6’, in which the conjugated

backbone is longer, the noncovalent stabilizing interactions

that were previously observed in compound 4 are notice-

Figure 8. Asymmetric units in compounds: a) 5, and b) 6; intramolecular

S···O, S···F, and H···F interactions are indicated by dotted lines.

on the solid-state by X-ray diffraction experiments). CCDC-

867252 (5) and CCDC-867251 (6) contain the supplementa-

ry crystallographic data for this paper. These data can be

obtained free of charge from The Cambridge Crystallo-

graphic Data Centre via www.ccdc.cam.ac.uk/data_request/

cif.

ACHTUNGTRENNUNGable, even if these contributions remain relatively weak

(NBO analysis; see the Supporting Information, Table S1).

Moreover, for these compounds, the electron density, 1(r),

at each bond critical point (BCP) varies from 0.016 and

ꢀ3

0.020 ea_oand, therefore, is within the range of the hydro-

gen bonds (see the Supporting Information, Table S2).

Crystallographic data that were recorded by X-ray diffrac-

tion on single crystals of compounds 5 and of 6 argue for

the existence of these intramolecular noncovalent interac-

tions. The experimental S···O, S···F, and H···F distances are

similar to the calculated values and the dihedral angles are

weakened (0.3–158). It is worth noting that the experimental

angles are narrower than their calculated ones because the

packing effect plays a crucial role in the solid state (Figure 8

and the Supporting Information, Figure S5, for more details

Optical and electronic properties of compounds 5 and 6: The

absorption properties of compounds 5 and 6 have been re-

corded for their solutions in CHCl₃(ꢅ10^ꢀ5m); these com-

pounds show absorption maxima at 397 and 399 nm, respec-

tively, and high molar extinction values of about 50ꢅ

10³Lmol^ꢀ1cm^ꢀ1(Table 3). Their conjugation properties, as

obtained from solution absorption measurements, are within

the same range as those of other well-designed five-ring p-

type organic semiconductors.^[19,20]Compared to all of the

Table 3. Electrochemical and optical data for oligomers 5 and 6, as well as a comparison of the experimental band-gaps in compounds 5 and 6 with the

calculated values in analogous compounds 5’ and 6’.

Absorption

CHCl₃(ꢅ10^ꢀ4m)

l_max[nm] (e [molL^ꢀ1cm])

Emission

Oxidation^[d]

Reduction^[d]

Gap [eV]

[V] (vs. SCE)

E_ox2E_red1

F_f^[a]

E_ox1

E_red2

optical

electrochemical

5

5’

397 (51500)

450

0.76

1.15

1.52

ꢀ1.89

ꢀ1.95

3.12

3.04

3.13

435.7^[b]381.8^[c]

2.85^[b]

3.25^[c]

3.10

6

6’

399 (48500)

451

0.8

1.00

1.36

ꢀ1.93

ꢀ2.11

2.93

3.14

433.4^[b]379.4^[c]

2.86^[b]

3.27^[c]

ꢀ

[a] Determined in CHCl₃by using 9,10-diphenylanthracene as a reference. The p p* transitions were determined by using TD-DFT calculations at the

[b] B3LYP/6-31G**, and [c] B3LYP/6-31G**//BHandHLYP/6-31G** levels of theory. [d] CH₃CH₂CN, Bu₄NPF₆, Pt, scan rate: 0.1 Vs^ꢀ1

Chem. Eur. J. 2013, 00, 0 – 0

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F. Serein-Spirau et al.

above compounds, the red-shifted absorption maxima of

compounds 5 and 6 reveal increased conjugation of the

p sysACHTUNGTRENNUNGtem, in good agreement with the higher values of the

directly related to the more-important presence of attractive

fluorine atom on the structure. The higher number of fluo-

rine electron-withdrawing atoms is introduced onto the p-

conjugated backbone, the lower the LUMO level of the

oligomer.

From these experimental and theoretical studies

(Table 3), the HOMO–LUMO gaps of these five-ring

oligomers are within the same range (2.9–3 eV).

much-more-important DE^psplitting values (3.16 and 3.33 eV

for compounds 5’ and 6’, respectively) and with the much-

narrowed calculated HOMO–LUMO gaps (3.13 eV for com-

pound 5’ and 3.14 eV for compound 6’; Table 3). Moreover,

the red-shifted experimental absorption maxima of real

compounds 5 and 6 must be compared to the absorption

maximum (l_max=374 nm) of the analogous completely un-

ꢀ

substituted phenylene thienylene five-aromatic-ring linear

Conclusions

oligomer,^[29]which reveals much-more-extended conjuga-

tion. This result is essentially due, on the one hand, to the

additional noncovalent intramolecular sulfur···oxygen,^[9,30,31]

sulfur···fluorine, and hydrogen···fluorine interactions,^[19,20]

which planarize the p-conjugated skeleton, and, on the

other hand, to strong interactions between the molecular or-

bitals of the fragments. An emission band is observed at

450 nm (l_exc=397 nm) for solutions of compounds 5 and 6

in CHCl₃. No changes in the emission spectra of these com-

pounds were observed on changing the concentration of the

solution, thus indicating the absence of excimers. Compared

to the emission quantum field of pentathiophene (0.4 in

CH₂Cl₂),^[32]the solution fluorescence properties of com-

pounds 5 and 6 are significantly higher, with emission quan-

tum fields of 0.76 and 0.8 in CHCl₃, respectively, taking

9,10-diphenylanthracene as a reference; these values are

ꢀ

The elaboration of thienylene phenylene sequences by al-

ternatively introducing 2,5-dialkoxy- and polyfluoro sub-

stituents onto phenylene motifs is an easy method for the

construction of soluble and fully p-conjugated oligomeric ar-

chitectures. These oligomers show extended inter-ring conju-

ꢀ

gation, as revealed by a small p p* gap and high experi-

mental splitting (DE^p) between the p orbitals that are delo-

calized over the three involved fragments, that is, 2,5-di-

AHCTUNGTREGaNNUN lkoxyphenylene, polyfluorophenylene, and thiophene. The

small value of the HOMO–LUMO gap is mainly due to the

energetic positions of the isolated fragments that are in-

volved, which increase the HOMO level, caused by the 2,5-

dialkoxyphenylene entity, and decrease the LUMO level,

caused by the polyfluorobenzene motif. Moreover, the pres-

ence of cumulative intramolecular noncovalent S···O, S···F,

and H···F interactions, which favor small dihedral angles

inside the three-ring sequences, consequently lead to good

p-orbital overlap and contribute to enhanced p-conjugation.

In these systems, these intramolecular attractive nonbonding

S···O, S···F, and H···F interactions are intrinsic properties of

comparable to the quantum yields of unsubstituted phenyl-

[29]

ꢀ

ene thienylene oligomers (0.7).

The electrochemical behavior of compounds 5 and 6 were

investigated by using cyclic voltamperometry of solutions in

propionitrile (ꢅ10^ꢀ3m) with Bu₄NPF₆(0.1m) as a supporting

electrolyte, a calomel saturated electrode as a reference

electrode, and a platinum wire as a working electrode. The

anodic scans were recorded between 0 and 1.9 V (vs. SCE)

and exhibited two oxidation waves. The first wave, at about

1.15 V versus SCE for compound 5 and about 1.00 V versus

SCE for compound 6, can be attributed to the formation of

the corresponding cation radical and the second wave can

be attributed to the formation of the dication at 1.52 and

1.36 V versus SCE, respectively (Table 3 and the Supporting

Information, Figure S6). These relatively high oxidation po-

tentials suggest a rather low HOMO level in these com-

pounds, in agreement with the theoretical data; the Kohn–

Sham values for the HOMO levels are ꢀ5.02 eV for com-

pound 5’ and ꢀ5.22 eV for compound 6’. Moreover, the rela-

tive positions of the oxidation potentials for compounds 5

and 6 are directly associated to the number of electronically

attractive fluorine atoms on the molecule, which makes elec-

tron abstraction difficult. Cathodic scans under the same ex-

perimental conditions failed and differential impulsion volt-

ꢀ

thienylene (2,5-dialkoxyphenylene or polyfluorophenylene)

sequences and result in both electrostatic and orbital contri-

butions. More generally, in thienylene (2,5-dialkoxyphen

ene or polyfluorophenylene) sequences, the planarization

ꢀ

yl-

U

and full intramolecular conjugation of the conjugated back-

bone are joint consequences of the presence of fluorinated

and alkoxy substituents on the phenylene rings, with the

latter groups having been introduced to confer solubility on

the resulting p-conjugated nanostructure. As indicated by

the crystallographic data of symmetrical oligomer 5 (see the

Supporting Information), face-to-face intermolecular p-

stacking interactions are formed between such planar nano-

structures; this type of arrangement is suitable to reach su-

perior electronic mobilities in organic materials to develop

organic transistors or photovoltaic cells. In addition, the

relevance of the association of the thienylene motif to the

dialkoxyphenylene and polyfluorinated phenylene fragments

clearly appears to be appropriate for narrowing the

HOMO–LUMO gap without raising the HOMO level. Con-

sequently, devices that are developed with such high-pow-

ered p-conjugated materials will be more stable towards oxi-

dation and will show improved performance.

ACHTUNGTRENNUNGamperometry allowed us to measure the two reduction po-

tentials, which corresponded to the formation of the radical

anion and the dianion, respectively. The reduction poten-

tials, which are ꢀ1.89 and ꢀ1.95 V versus SCE for com-

pound 5 and ꢀ1.93 and ꢀ2.11 V versus SCE for compound

6, reveal the electronic affinity of these oligomers, which is

&

12

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ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 0000, 00, 0 – 0

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These are not the final page numbers!

Highly p-Conjugated Thienylene-Substituted Phenylene Oligomers

FULL PAPER

50 mL), filtered, and washed with a solution of ammonium fluoride

(50 mL) in water and a saturated aqueous solution of sodium chloride

(50 mL). After drying over sodium sulfate, the mixture was concentrated

and the light-yellow solid was purified by column chromatography on

silica gel (pentane/Et₂O, 90:10) to give compound 2 as a white solid in

75% yield (3.46 g).

M.p. 1608C; ¹H NMR (400 MHz, CDCl₃, 258C): d=7.66 (d, J=3.5 Hz,

2H; H_Th), 7.55 (d, J=3.5 Hz, 2H; H_Th), 7.19 ppm (t, J=4.2 Hz, 2H; H_Th);

¹³C NMR (101 MHz, CDCl₃, 258C): d=145.3 (C_Th), 142.8 (C_Ph), 130.2

(C_Ph), 128.3 (C_Th), 127.8 (C_Th), 127.4 ppm (C_Th); ¹⁹F NMR (376 MHz,

CDCl₃, 258C): d=ꢀ140.8 ppm; IR (neat KBr): n˜ = =3373, 1639, 1477,

1420, 1347, 1295, 1223, 1072, 967, 853, 838, 758, 716, 701 cm^ꢀ1; UV/Vis

(CHCl₃): l_max=309 nm; MS (FAB⁺): m/z (%): 314 (19) [M], 307 (30).

Theoretical Calculations

Calculations were performed with the Gaussian 03 program^[33]by using

the density functional theory method.^[34]The various structures were fully

optimized at the B3LYP level,^[35]which employs Beckeꢂs three-parameter

exchange functional^[35a]and the Lee–Yang–Parr correlation functional,^[35c]

with the 6-31GACHTUNGTRENNUNG

(d,p) basis set.^[36]All atoms were augmented with a single

set of polarization functions. Their second derivatives were calculated to

check that the optimized structures were true minima on the potential-

energy surface. All of the total energies were zero-point energies (ZPEs)

and temperature corrected by using un-scaled density functional frequen-

cies.

Taking into account the RX structures, for the three- and five-ring com-

pounds, only their isomers in which the two sulfur atoms are in anti posi-

tions have been calculated.

For the assignment of the PE spectra, ionization energies^[37]were calcu-

lated as previously suggested by Stowasser and Hoffmann.^[38]Other au-

thors, such as Arduengo et al.^[39]or the groups of Werstiuk^[40]and Rade-

macher,^[40]used this method to analyze different PE spectra.

The spectroscopic data agree with those reported in the literature.^[20]

1,4-Bis(2-thienyl)-2,5-difluorobenzene (3): Compound 3 was prepared ac-

cording to the same procedure as compound 2, with 1,4-dibromo-2,5-di-

fluorobenzene (15 mmol, 4.1 g), 2-tributylstannylthiophene (30 mmol,

11.2 g), bis(triphenylphosphine)dichloropalladium (210 mg, 2 mol%), and

triphenylphosphine (2.4 mmol, 0.63 g, 16%mol) in anhydrous THF/DMF

(1:1, 60 mL). Purification by column chromatography on silica gel (pen-

tane/Et₂O, 90:10) afforded compound 3 as a pale-yellow solid in 80%

yield (3.33 g).

Molecular orbitals were plotted by using the Molekel package.^[41]

NBO population analysis^[42]was performed to determine the total charg-

es on each atom and to check whether strong or weak stabilizing interac-

tions existed between a filled orbital and an empty orbital in these stud-

ied systems.

M.p. 1228C; ¹H NMR (400 MHz, CDCl₃, 258C): d=7.51 (d, J=3.6 Hz,

2H; H_Ph), 7.41 (m, 4H; H_Thand H_Ph), 7.14 ppm (dd, J=5.1 Hz, J=

3.6 Hz, 2H; H_Th); ¹³C NMR (101 MHz, CDCl₃, 258C): d=156.1 (C_Ph),

153.6 (C_Ph), 135.8 (C_Th), 127.9 (C_Th), 126.8 (C_Th), 121.9 (C_Th), 115.5 ppm

(C_Ph); ¹⁹F NMR (376 MHz, CDCl₃, 258C): d=ꢀ119.1 ppm; IR (neat

KBr): n˜ =3453, 2369, 1728, 1635, 1487, 1439, 1357, 1285, 1215, 1172, 1057,

The electron density of the optimized structures was subjected to Atoms-

In Molecules analysis^[27](QTAIM analysis) by using AIMAll software.^[43]

UV/Vis absorption spectra were calculated by using the time-dependent

DFT formalism within the Gaussian package at the B3LYP/6-31G** or

B3LYP/6-31G**//BHandHLYP/6-31G**^[44]levels of theory.

974, 868, 830, 820, 794, 785, 712, 690 cm^ꢀ1; UV/Vis (CHCl₃): l_max

=

322 nm; MS (FAB⁺): m/z (%): 278 (70) [M], 154 (100).

The spectroscopic data agree with those reported in the literature.^[14,45]

2-(2,5-Dimethoxyphenyl)-5-(perfluorophenyl)thiophene (4): Bromopen-

tafluorobenzene (4.2 mmol, 1.04 g), 2-(1,4-dimethoxyphenyl)-5-tributyl-

stannylthiophene (7, 4.2 mmol, 2.15 g), and tetrakis(triphenylphosphine)-

palladium (245 mg, 5 mol%) were introduced into a two-necked round-

bottomed flask (100 mL) under a nitrogen atmosphere in anhydrous

THF/DMF (1:1, 6 mL). The mixture was stirred at 808C for 65 h, the

THF was removed, and a 3m solution of ammonium fluoride (100 mL) in

water and CH₂Cl₂(120 mL) were added. The mixture was stirred vigo-

rously for 2 h and the organic phase was extracted with CH₂Cl₂(3ꢅ

50 mL), filtered, and washed with a saturated aqueous solution of sodium

chloride (50 mL). After drying over sodium sulfate, the mixture was con-

centrated and the crude product was purified by column chromatography

on silica gel (pentane/CH₂Cl₂, 90:10) to give compound 3 as a pale-

yellow solid in 43% yield (690 mg).

Experimental Section

Photoelectron spectroscopy: The photoelectron spectra were recorded on

a PerkinElmer 0018 instrument that was equipped with a 1278 cylindrical

analyzer and monitored by using a microcomputer that was supplement-

ed with a digital analogic converter. The spectra were calibrated to the

known auto-ionization energies of He at 4.99 eV (He(II)/He(I)) and Xe

at 12.13 and 13.44 eV. All of the products were vaporized thanks to the

beam heat at ꢅ10^ꢀ5mbar. A stable temperature of the beam was main-

tained to vaporize enough of the compounds to obtain intense spectra.

General procedures: DMF, THF, CH₂Cl₂, pentane, and MeCN were

dried and distilled under a nitrogen atmosphere prior to use. The starting

materials (see the Supporting Information) were purchased (Alfa and Al-

drich) and used without further purification. ¹H, ¹³C, and ¹⁹F NMR spec-

tra were recorded on a Brucker AC 400. Chemical shifts (d, in ppm) are

referenced to TMS by using CHCl₃(d=7.27 ppm) and CDCl₃(d=

M.p. 1428C; ¹H NMR (400 MHz, CDCl₃,258C): d=7.55 (d, J=4.0 Hz,

1H; H_Th),7.5 (d, J=4.0 Hz, 1H; H_Th), 7.24 (d, J=3 Hz, 1H; H_Ph), 6.95 (d,

J=9 Hz, 1H; H_Ph), 6.86 (dd, J=9 Hz, J=3.0 Hz, H_Ph), 3.92 (s, 3H;

OMe), 3.8 ppm (s, 3H; OMe); ¹³C NMR (101 MHz, CDCl₃, 258C): d=

1

77.70 ppm) as internal standards for the H and ¹³C NMR spectra, respec-

ꢀ

153.8 (C_Ph), 150.1 (C_Ph), 144.0 (C_PhF), 142.1, 139.6 (C_PhF), 138.0 (C_Ph

F), 129.9 (C_Th), 126.2, 125.4 (C_Th), 123.1 (C_Ph), 114.0 (C_Ph), 113.7 (C_Ph),

113.1 (C_Ph), 110.3, 56.3 (OCH₃), 55.8 ppm (OCH₃); ¹⁹F NMR (376 MHz,

CDCl₃, 258C): d=ꢀ162.3, ꢀ156.5, ꢀ139.7 ppm; IR (neat KBr): n˜ =2839,

1610,1581, 1535, 1518,1481, 1407, 1340, 1313, 1288, 1253, 1221, 1170,

tively. IR spectra were recorded on a PerkinElmer 1000 spectrophotome-

ter and absorption spectra were recorded on a Hewlett Packard 8453

spectrophotometer. Melting points were measured on an Electrothermal

9100 apparatus. Mass spectrometry was performed on a JEOL JMS-DX

300 apparatus by using the FAB⁺ionization mode or on a THERMO

FINNIGAN MAT 95 apparatus by using the EI ionization mode. Ele-

mental analysis was performed by the Service Analyses de lꢂUniversitꢁ

Montpellier II. Detailed synthetic procedures of compounds 1, 7, 8, 9, 10,

11, 12, and 14 are provided in the Supporting Information.

1050, 1019, 974, 844, 801, 791, 724, 648 cm^ꢀ1; UV/Vis (CHCl₃): l_max

=

345 nm; MS (FAB⁺): m/z (%): 386 [M]; elemental analysis calcd (%) for

C₁₈H₁₁F₅O₂S: C 55.95, H 2.88; found: C 55.89, H 2.97.

1,4-Bis-2’-(5’-perfluorophenylthienyl)-2,5-dioctyloxybenzene (5): 1,4-Di-

AHCTUNGTRENNUNG

1,4-Bis(2-thienyl)-2,3,5,6-tetrafluorobenzene (2): 1,4-Dibromo-2,3,5,6-tet-

rafluorobenzene (15 mmol, 4.61 g), 2-tributylstannylthiophene (30 mmol,

11.2 g), bis(triphenylphosphine)dichloropalladium (210 mg, 2 mol%), and

triphenylphosphine (2.4 mmol, 0.63 g, 16% mol) were introduced into a

round-bottomed flask (250 mL) under a nitrogen atmosphere in anhy-

drous THF/DMF (30 mL, 1:1). The mixture was stirred at 808C for 18 h,

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

bottomed flask (100 mL) under a nitrogen atmosphere in anhydrous

THF/DMF (1:1, 20 mL). The medium was stirred at 808C for 72 h, the

THF was removed, and a 3m solution of ammonium fluoride (100 mL) in

water and CH₂Cl₂(120 mL) were added. The mixture was stirred vigo-

rously for 2 h and the organic phase was extracted with toluene (3ꢅ

50 mL), filtered, and washed with a saturated aqueous solution of sodium

the THF was removed, and

(250 mL) in water and Et₂O (250 mL) were added. The mixture was stir-

red vigorously for 1 h and the organic phase was extracted with Et₂O (3ꢅ

a 3m solution of ammonium fluoride

Chem. Eur. J. 2013, 00, 0 – 0

ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

&

13

&

ÞÞ

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F. Serein-Spirau et al.

ꢀ

chloride (50 mL). After drying over sodium sulfate, the mixture was con-

centrated and the crude product was purified by column chromatography

on silica gel (pentane/toluene, 95:5) to give compound 5 as an orange

solid in 40% yield (632 mg).

112.4 (C_PhBr), 70.4 (O CH₂), 69.9 (O CH₂), 31.8 (CH₂, 2C), 29.34

(CH₂), 29.33 (CH₂), 29.27 (CH₂), 29.26 (CH₂), 29.24 (CH₂), 29.22 (CH₂),

26.3 (CH₂), 26.0 (CH₂), 22.67 (CH₂), 22.63 (CH₂), 14.1 (CH₃), 14.0 ppm

(CH₃); ¹⁹F NMR (376 MHz, CDCl₃, 258C): d=ꢀ162.8, ꢀ157.2,

ꢀ140.1 ppm; IR (neat KBr): n˜ =3089, 2956, 2927, 2872, 2857, 1531, 1516,

1499, 1489, 1217, 1037, 806, 794 cm^ꢀ1; HRMS (FAB⁺): m/z calcd for

C₃₂H₃₈BrF₅O₂S: 660.1696; found: 660.1686.

1

M.p. 182.58C; H NMR (400 MHz, CDCl₃, 258C): d=7.59 (d, J=3.71 Hz,

2H; H_Th), 7.52 (d, J=3.71 Hz, 2H; H_Th), 7.31 (s, 2H; H_Ph), 4.14 (t, J=

ꢀ

6.26 Hz, 4H; OCH₂), 1.94 (m, 4H; O CH₂CH₂), 1.65–1.20 (m, 20H;

CH₂), 0.87 ppm (t, J=7 Hz, 6H; CH₃); ¹³C NMR ( 101 MHz, CDCl₃): d=

ꢀ

149.4 (C_Ph), 141.9 (C_PhF), 129.8, 128.1, 126.7, 125.2, 125.1, 124.8, 122.7,

77.2 (OCH₂), 69.9 (OCH₂), 31.8 (CH₂), 29.4 (CH₂), 29.2 (CH₂), 26.4

(CH₂), 22.7 (CH₂), 14.1 ppm (CH₃); ¹⁹F NMR (376 MHz, CDCl₃, 258C):

d=ꢀ162.2, ꢀ156.5, ꢀ139.7 ppm; IR (neat KBr): n˜ =3087, 2950, 2923,

2876, 2856, 1541, 1517, 1500, 1480, 1217, 810, 788 cm^ꢀ1; UV/Vis (CHCl₃):

l_max=397 nm; HRMS (FAB⁺): m/z calcd for C₄₂H₄₀F₁₀O₂S₂: 830.2310;

found: 830.2290.

Acknowledgements

This work was supported by the Ministꢀre de la Recherche and by the

Centre National de la Recherche Scientifique (CNRS). To perform the

theoretical work, we acknowledge the GENCI (Grand Equipement Na-

tional de Calcul Intensif) for granting us access to the HPC resources of

the Institut du Developpement de Ressources en Informatique Scientifi-

que (IDRIS, Orsay, France), under allocation 2012 (i2012080045). In ad-

dition, we gratefully acknowledge the allocation of beam-time for the ex-

periments on the microfocus beamline (ID13) at the European Synchro-

tron Radiation Facility.

1-[2’-(5’-Phenylthienyl)]-4-[2“-(5”-perfluorophenylthienyl)]-2,5-dioctyl-

A

ACHTUNGTRENNUNGbenzene (6): 1-Bromo-4-[2’-(5’-perfluorophenylthienyl)]-2,5-dioctACHTUGNTRENyNUGN l-

ACHTUNGTRENNUNG

phene (14, 0.768 mmol, 345 mg), cesium fluoride (1.13 g, 7.5 mmol), pal-

ladiumdibenzylidene acetone (0.015 mmol, 9 mg, 2 mol%), and triphenyl-

phosphine (0.06 mmol, 16 mg, 8%mol) were introduced into a two-

necked round-bottomed flask (100 mL) under a nitrogen atmosphere in

anhydrous THF (20 mL). The medium was stirred at 808C for 24 h, the

THF was removed, and a 3m solution of ammonium fluoride (50 mL) in

water and CH₂Cl₂(30 mL) were added. The mixture was stirred vigorous-

ly for 2 h and the organic phase was extracted with CH₂Cl₂(3ꢅ30 mL),

filtered, and washed with a saturated aqueous solution sodium chloride

(50 mL). After drying over sodium sulfate, the mixture was concentrated

and the black solid was purified by column chromatography on silica gel

(pentane/CH₂Cl₂, 90:10) to give compound 6 as a pale-yellow solid in

38% yield (213 mg).

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M.p. 128.38C; H NMR (400 MHz, CDCl₃, 258C): d=7.68 (m, 2H), 7.60–

7.50 (m, 3H), 7.40 (m, 3H), 7.32 (d, J=3.80 Hz, 1H), 7.29 (s, 1H), 7.28

(s, 1H), 4.14 (t, J=6.47 Hz, 2H; OCH₂), 4.12 (t, J=6.32 Hz, 2H; OCH₂),

ꢀ

1.95 (m, 4H; O CH₂CH₂), 1.65–1.20 (m, 20H; CH₂), 0.88 ppm (m, 6H;

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145.2–142.6 (m, 2C, C F), 144.2 (C_Th), 142.1 (C_Th), 140.7–138.2 (m, C F),

139.2–136.8 (m, 2C, C F), 138.5 (C_Th), 134.5 (C_Ph), 129.7 (C_ThH), 128.8

(2C, C_PhH), 127.3 (C_PhH), 126.4 (C_ThH), 126.3 (C_Th), 125.6 (2C, C_Ph

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ꢀ

H), 124.7 (C_ThH), 123.6 (C_Ph), 123.0 (C_ThH), 121.7 (C_Ph), 111.9 (C_Ph

ꢀ

H), 111.8 (C_PhH), 110.4 (C_Ph), 69.74 (OCH₂), 69.73 (OCH₂), 31.86

(CH₂), 31.85 (CH₂), 29.5 (2C, CH₂), 29.4 (2C, CH₂), 29.33 (CH₂), 29.27

(CH₂), 26.40 (CH₂), 26.39 (CH₂), 22.68 (CH₂), 22.66 (CH₂), 14.10 (CH₃),

14.06 ppm (CH₃); ¹⁹F NMR (376 MHz, CDCl₃): d=ꢀ162.8, ꢀ157.2,

ꢀ140.2 ppm; IR (neat KBr): n˜ =3083, 2951, 2922, 2872, 2853, 1597, 1541,

1517, 1503, 1486, 1213, 805, 798, 753 cm^ꢀ1

; UV/Vis (CHCl₃): l_max=

399 nm; HRMS (FAB⁺): m/z calcd for C₄₂H₄₅F₅O₂S₂: 740.2781; found:

740.2763.

1-Bromo-4-[2’-(5’-perfluorophenylthienyl)]-2,5-dioctyloxybenzene (13):

Freshly prepared compound 8 was diluted in distilled THF (40 mL) and

compound 12 (4 mmol, 2.15 g), cesium fluoride (8 mmol, 1.2 g), palla-

diumdibenzylidene acetone (0.08 mmol, 46 mg, 2 mol%), and triphenyl-

phosphine (0.32 mmol, 93 mg, 8%mol) were introduced into a round-

bottomed flask (100 mL) that was fitted with a condenser under a nitro-

gen atmosphere. The reaction was heated at 808C and stirred for 72 h.

After cooling, the solvent was removed and the residue was diluted with

CH₂Cl₂(50 mL). The organic phase was extracted with CH₂Cl₂(3ꢅ

50 mL) and washed with water. After drying over sodium sulfate, it was

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ꢀ

6.5 Hz, 4H; OCH₂), 1.85 (m, 4H; O CH₂CH₂), 1.65–1;20 (m, 20H;

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ꢀ

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126.5 (C_Ar), 125.0 (C_ArH), 122.1 (C_Ar), 117.8 (C_ArH), 113.2 (C_ArH),

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Highly p-Conjugated Thienylene-Substituted Phenylene Oligomers

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Received: October 29, 2012

Published online: && &&, 0000

Chem. Eur. J. 2013, 00, 0 – 0

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F. Serein-Spirau et al.

ꢀ

p in the sky: Thienylene phenylene

oligomers with fluorinated and di-

Oligomers

AHCTUNGTRENNaGUN lkoxylated phenylene fragments have

J.-C. Florꢀs, M.-A. Lacour,

been designed and prepared. UV pho-

toelectron spectroscopy and DFT cal-

culations highlight how the resulting

strong conjugation depends on the

energetics of the p orbitals of the

molecular fragments, which are related

to the nature of the substituents (F,

OMe) on the phenylene groups (see

figure).

X. Sallenave, F. Serein-Spirau,*

J.-P. Lꢀre-Porte, J. J. E. Moreau,

K. Miqueu, J.-M. Sotiropoulos,

D. Flot ......................... &&&& — &&&&

Comprehensive Analysis of Fragment

Orbital Interactions to Build Highly p-

Conjugated Thienylene-Substituted

Phenylene Oligomers

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Article Doi

Comprehensive analysis of fragment orbital interactions to build highly π-conjugated thienylene-substituted phenylene oligomers

DOI: 10.1002/chem.201203869

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Authors:

Article abstract of DOI:10.1002/chem.201203869

Full text of DOI:10.1002/chem.201203869

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