Synthesis of low band gap polymers - a challenge for organic chemists

ELSEVIER

Synthetic Metals 71 (1995) 2275-2278

OFLOWBANDGAPPOLYMERS-

SYNTHESIS

M. Hanack*,

ACHALLENGEFORORGANIC

K. Diirr, A. Lange, J. Oslo Barcina,

CHEMISTS

J. Pohmer and E. Witke

Institut fir Organ&he Chemie, Lehrstuhl fir Organische Chemie II der Universitit Auf der Morgenstelle 18, D-72076 Tiibingen, Germany

Tiibingen,

Abstract Stable intrinsic

semiconductors,

using our “shish-kebab” phthalocyanine tetrazine

which exhibit conductivities

(PC) or 2,3-naphthalocyanine

(tz), substituted

acid dinitrile,

tetrazines,

fumarodinitrile,

sponding transition The intrinsic

dicyanoacetylene,

The electrical

triazines,

and dicyane.

Bridged

of all these compounds

kebab” (MacM)

metal complexes

are a result of the low oxidation

especially

are discussed

[MacM(L)ln in various phyrine

transitionmetalmacrocycles in which

oxidation

the UV- and MoRbauer spectra (for the corresponding

[MacM(L)],

but

bridging

“shish

metalmacrocycles ligands

(L). In

metals are e.g. Fe, Ru, OS, Co, Rh

states

systems

(TBP),

transition

with bidentate

the transition

heteroaromatic

[l].

As macrocycles

phthalocyanine also

macrocycles

extended a-systems like 1,2- or (1,2-, 2,3-NC). anthracenocyanine anthrenocyanine (Phc.) are used [l]. As bifunctional organic donor molecules,

of the corre-

ligands and due to

properties

iron compounds)

for the

of these compounds.

azide (Ng-) for transition

containing

more

2,3_naphthalocyanine phen(Ant) or bridging ligands (L) e.g. pyrazine (pyz),

metals in the oxidation

state +3 (11

(Fig. 1).

0379-6779/95/$09.50 0 1995 Elsevier Science S.A. All rights reserved SSDI 0379-6779(94)03256-6

The coordination practically

polymers

or oligomers

insoluble in organic solvents,

have been synthesized

[MacM(L)ln

using metallomacrocycles

RdPcM and

RgPcM with R = t-bu, et, OR’, (R’ = ‘Cg - Clo), Ru, which are substituted

in peripheric

are

but soluble oligomers M = Fe,

positions.

(Mac) the

(PC), tetrabenzopor-

s-tetrazine (tz) and others (see below), for metals in the oxidation state +2, or cyanide (CN-), thiocyanate (SCN-) or are employed

e.g. s-

RESULTSANDDISCUSSION

[l]

are reacted

and the characterization

potential of the bridging

in respect to the intrinsic semiconducting

in a large variety by using the so-called

approach

systems,

e.g. tetrafluoroterephthalic

bridged systems [MacM(L)]n.

and physical properties,

stacked

but also special organic dinitriles,

We report about the preparation

INTRODUCTION

are synthesized

by

wacM(L)],.

the low lying LUMO in the corresponding

bridged macrocyclic

can be easily prepared

with M e.g. Fe, Ru, OS and Mac =

[MacM(L)]n.

(2,3-NC) are used. The bridging ligands (L) are special heteroaromatic

triazine (tri), substituted

metal complexes

conductivities

of 0.1 S/cm without any doping process

Hereby stacked transition metal macrocycles

approach.

The polymers

so obtained exhibit

non-soluble

interesting

and

electrical

soluble

coordination

and non-linear

optical

properties. The soluble polymers [RxMacM(L)], form Langmuir Blodgett films and they have been recently used successfully as sensors.

M. Hanack et al. / Synthetic Metals 71 (1995) 22752278

2276

(L = tz, meztz) and the bridged systems [MacM(L)],

(L = tz,

meztz).

to other

The tetrazine

bridged compounds

bridged

systems,

wacM(L)],

in contrast

with M =: Fe, Ru or OS and

L e.g pyz or dib, show already good semiconducting properties without external oxidative doping (uRT = 0.05 0.3 S/cm). The dc-powder cyclic transition

conductivities

different

listed in Table 1. The bridged

complexes

macrocycles, distance

Fe’+, Fe&. Co'+, Co%, Ru’+, Mnz4, Mr?, Cr3+

bridged

in the non-doped

taining a variety of structurally L = dabco, pyz, tz, me$z

M =

of various

metal oligomers

macro-

state con-

bridging

ligands are

[MacM(L)],

with

and tri, contain cofacially arranged

which are separated

by approximately

the same

(about 600 pm). Table 1 also shows the conductivity

data of the corresponding

monomers

MacM(L)2

for compari-

son.

r N..

//

L=N

A systematic

N\ Nd

wN*

investigation

of the influence

ligands on the semiconducting

properties

of the bridging

in [MacM(L)ln

re-

veal, that changing L, e.g from dabco over pyz to tz leads to a

0 =

pcz-, R,Pc*-,

R,Pc’-,

1,2-Nc2-, 2,3-Nc2-,

TBP’-

steady increase

of the semiconducting

ternal oxidative

doping.

Powder

0.1 S/cm can be reached tuted tetrazine complexes Schematic transition

structure

a transition

on the electrical properties

of

and it will be shown that the combination

of

metal macrocycle

with special

forming

the coordination

polymer

systems,

which exhibit intrinsic conductivities,

show very good semiconducting

but also substi-

bridging

[MacM(L)], properties

ligands

can lead to

(Table 1). complexes

PcM(L)?

of the bridging

ligand

phthalocyaninato

and

external

complexes

[MacM(L)ln.

on the conductivity Many different

fluence on the general behaviour nation polymers. double tetrazine (me+)

bonds),

As bridging pyrazine

about the influence of the bridged

dures as in the case of the oligomers

except that the molar

ratio of the ligands L and the transition

metal phthalocyanines

is different.

monomers process

They

PcM(L)z

into the oligomers

upon the bridging

show

ligands have

and electronic

of the corresponding

in-

coordi-

ligands first e.g. dabco (without

(pyz),

(tz), and its derivatives are used and the powder

sponding bridged coordination

bridging

structural

1,4-diisocyanobenzene

(dib),

e.g. 3,6-dimethyl-s-tetrazine conductivities

polymers

of the corre-

are compared.

PcFe, PcRu, PcOs, and 7,3-NcFe react with tetrazine (tz) (me$z), depending on the conditions,

and dimethyltetrazine with formation

of the corresponding

insolating

can be transformed [PcM(L)],,

behaviour.

The

by a simple thermal which then depending

ligands exhibit high intrinsic conductivities

(Table 1). The following

conclusion

monomers

[PcFe(dabco)],

can be drawn no r-orbitals,

observed

is an insulator.

for the pyrazine-bridged

which exhibit conductivities

2,3-naphthalocyaninatotransitionmetal

been used to study their special

dabco,

using the same proce-

interact with the metallomacrocycle are reported

(L = e.g.

pyz, tz; M = Fe, Ru, OS) are prepared

dabco is a ligand containing

investigations

triazine,

ligands in such

in other words, without

oxidative doping. Systematic

(mq_tz),

and others as the bridging

The monomeric

metal complexes

In this report we concentrate

by using s-tetrazine,

of bridged macrocyclic

PcM

these compounds,

without ex-

in the order of

e.g. 3,6-dimethyl-s-tetrazine

p-diaminotetrazine, Figure 1.

properties

conductivities

MacM(L)?

However, tetrazine

from Table

1:

which are able to

(see below),

An increase

the complex

in conductivity

compounds

is

[MacM(pyz)],,

in the low semiconducting

region.

by changing the bridging ligand from pyrazine to sthe conductivity

is increased

by 3 to 5 orders

magnitude without external oxidative doping comparison with the corresponding monomers conductivity

increases

lo9 (Table 1).

of

(Table 1). In PcM(L)z the

even more by factors in between

lo7 -

2211

M. Hanack et al. / Synthetic Metalr 71 (199.5) 2275-2278

DC-Powder

Table 1

electrical conductivities

and bridged macrocyclic

of monomeric

transition metal com-

plexes (room temperature,

pressed pellets,

1 kbar).

phthalic

acid dinitrile

sponding

coordination

has been polymer

used to prepare

NCC=CCN

leads

[PcRu(CN)~C~],

URT [S/cm- ’J

which, as

shown in Table 1, also shows good semiconductive without external oxidative doping.

Compound

the corre-

[PcRu(CN)2F4C&

with

Using fumaric acid dinitrile corresponding polymer

the

to

properties

powder

conductivity

of

obT =

especially

the UV

10e2 S/cm. 10-10

PcFe(dabco)2 [PcRu(dabco)2

The electrical

10-10

x 1.4 CHC13],

and physical

3 x 10-12

and MoRbauer

[PcFe(pyz)l, PcFe@zh,

1 x 10-h < 10-o

to their intrinsic

tPcFe(tz)], PcRu(tz)2

2 x 10-2 < 10-11

strated with one example

in the following:

conductive

polymers

[PcRu(tz)ln PcOs(tz)2

1 x 10-2 4 x 10-S

tetrazines),

[PcFe(me$z)l,

4 x 10-3

fumaro

[PcRu(NH2)2tzl,

4 x 10-3

shown by the corresponding

IPcRup-(NH2)2CgH41n [PcRuC12(tz)],

5 x 10-o

dib or dabco.

3 x 10-3

broad bands in the UV/Vis/NIR

[pcos(PYz)ln

1 x 10-b

bridged

systems

Pcwtz)1,

1 x 10-2

maxima,

e.g.

[2,3-NcFe(pyz)l, [2,3-NcFe(tz) x 0.2 CHC13],

5 x 10-5

MWWI,

3 x 10-l

pyrazine-bridged

[(me)gPcFe(PYz)ln [(me)8PcFe(tz)ln

3 x 10-o

hibit normal UVNis

1 x 10-2

245 and 700 nm respectively,

[PcRu(me#ln [PcRu(tri)12

4 x 10-3

1200 and 2500 nm. The absorption

1 x 10-o

correlate

well with electrochemically

[PcRu(tri)],

2 x 10-4

between

the HOMO of the different

[PcRu(CN)~F~C&

1 x 10-3

the LUMO of the tetrazine in all the tetrazine-bridged

systems.

PcRuKW2C21

3 x 10-2

The broad band observed

of these

In addition to tetrazine tuted tetrazines,

used as the bridging sponding

and dimethyltetrazine

e.g. p-diaminotetrazine

oligomer

cally conductive

metals

other substi-

(NH2)2tz

have been

ligand to react with PcRu. Tr.2 corre-

[PcRu(NH2)2tzln

spectra

properties,

PcFe(pyz)2

also shows intrinsic con-

(for iron compounds)

coordination

and

all the intrinsically group

tz,

me2tz

triazine,

tetrafluoroterephthalic

exhibit

like

physical

properties

systems

All the intrinsically between for at

in respect

This is demon-

with

ligands

8 transition (substituted

acid

dintrile,

which

are not

in which L = e.g. pyz, conductive

spectra,

systems

show

e.g. for the tetrazine-

1250 and 2500 nm with different

[PcFe(tz)ln

1053 nm

at

1515 nm

(1.18 eV).

systems

[PcM(pyz)],

(0.75 eV)

The

and

corresponding

(M = Fe, Ru, OS) ex-

spectra with Soret- and Q-bands between but show no absorption

are assigned

to charge

macrocycle

to the **-orbital

Also the MiiRbauer

between

bands in the near infrared estimated

energy

melallomacrocycles

in the absorption

complexes

transfer

properties.

bridging

dinitrile

complexes

polymer are discussed

semiconducting

coordination

for the intrinsi-

transfer

spectra

gap and

from the metallo-

of s-tetrazine.

data of s-tetrazine

can be very well correlated

from the metalmacrocycle

coordinated

iron

with an internal charge

to the bridging

ligand with

a low oxidation potential.

ductivity Mohbauer Triazine

(tri) also forms coordination

shown in Table 1 show a powder values of the tetrazine-

oligomers,

conductivity

and pyrazine-bridged

in between

systems.

is linked to the central metal of the macrocycle

which as the

Triazine

(e.g. Fe or Ru)

via the 1,4-nitrogens.

in Table 2 in comparison

iron macrocycles

and the corresponding

For the tetrazine-bridged

dination

increase of the quadrupole

intrinsic

polymers

the bridging

conductivities

of this type of coor-

are due to the low oxidation

potentials

of

ligands, e.g. tz and me2tz. The low lying LUMO

of the bridging

ligand leads to a charge transfer

of the metal-

macrocycle on to the bridging ligand thereby inducing intrinsic conductivities.

cally

bridging

conductive

ligand can be used to prepare

coordination

polymers:

intrinsi-

p-tetrafluorotere-

splitting

is measured.

iron complexes with the data for the

pyridine

[MacFe(tz)], PcFe(tz)2 (+Q)

complexes. the isomer

whereas

a clear

even in comparison

This is a further indication

low band gap in the tetrazine-bridged

complexes,

for a

because this

effect can be explained

by the thermal activation

of electrons

of the highest occupied

band. As the contribution

of such de-

localized

electrons

to the occupation

of metal

centred

d-

orbitals is diminished, the increase in APQ is the result of the low band gap of the quasi one-dimensional chain structure of the tetrazine-bridged

Additional

complexes

shift 6 is similar to the monomeric to [PcFe(pyz)ln

The observed

data of s-tetrazine-coordinated

are summarized

complexes.

2278

Table 2

M. Hanack et al. I Synthetic Met&

MiiRbauer

data of monomeric

and bridged

PcFe

71 (1995) 2275-2278

CONCLUSIONS

complexes The bridged macrocyclic transition metal complexes described here are one of the first stable systems which exhibit Complex

6 [mm/s]

AEQ

b"-f'/sl

intrinsic conductivity,

they are thermally

quite stable and have

potential technical applications. R-PcFe

0.38

2.58

PcFe(py)2

0.26

2.02

PcFe(tz)2

0.15

1.79

PcFeWln

0.13

2.23

PcFe(me$z).O.S (Me)8PcFe

mqtz

0.36

2.67

0.38

2.55

REFERENCES

(Me)gPcFc(PY):!

0.26

1.97

](Me)8PcFe(tz)ln

0.14

2.11

peler, J. Koch, J. Metz, M. Mezger.

1.

a) M. Hanack, A. Datz, R. Fay, K. Fischer,

U. Kep-

0. Schneider,

(MeO)gPcFe

0.36

2.50

H.-J. Schulze, Handbook of Conducting Polymers;

(MeC)gPcFe(PY)2

0.25

1.95

T.A. Skotheim,

](MeC)8PcFe(tz)], PcFe(tri)2

0.15 0.20

2.19 1.79

1986. - b) M. Hanack, S. Deger, A. Lange, Coord. Chem. Reviews 1988, 83, 115. - c) H. Schultz,

[PcFe(tri)],

0.27

1.91

H. Lehmann,

[EtqPcFe(tz)], [Et4PcFe(tri)],

(Ed.), Marcel Dekker,

M. Rein, M. Hanack, Structure and

Bonding 74, J. W. Buchler, 0.27

1.82

Heidelberg, Materials,

New York,

(Ed.), Springer-Verlag,

1990. - d) M. Hanack, M. Lang, Adv. in press.