Syntheses and ESR characterizations of conjugated polymers with nitrogen atoms

Synthetic

Metals 85 (1997)

1683-1684

Syntheses and ESR characterizations of conjugated polymers with nitrogen atoms H. Goto, KIino, K. Akagi, and H. Shirakawa Institute of Muterials

Science, University of Tsukuba, Tsukuba, Ibaraki

305, Japan

Abstract We presentsynthesesandpropertiesof severalkindsof polyanilineandpolyaminopyridinederivatives. Polyanilinederivative with a stableradical group (PDDBO) and iodine-doped(doped-PmAPY) or oxidized polyaminopyridine(PlnAPYO) showedone or two “half-field” ESR signalsdueto hms= i 2, in additionto a signalat centralresonancefield. For thesepolymerswasstronglysuggested a possibilityof spinmultiplet stateincludingtriplet one. Keywords:

Polyaniline

and derivatives; Electron

spin resonance; Solution processing

1. Introduction

using POCl3 as a catalyst, according to Rhosemundreaction (Scheme2). After 24hrs,the productwaswashedwith methanol

E-Electronconjugatedpolymershave various functionssuch aselectrical conductivity, optical nonlinearity, and through-bond spin interaction. Conjugatedpolymers with ferromagnetism have beenattractingmuchattention [l-2]. Here we synthesized severalkinds of conjugatedpolymerscontainingnitrogen atoms andinvestigatedtheir polymerstructuresby meansof JR andUVVis spectroscopies.Furthermore, we synthesized a novel polyanilinederivative substitutedwith a stableradical groupand examinedits electronspinstructureby ESR.

Cul, KzCQ

PpAN

(poly-paniline)

2. Experimental 2-I.

S’theses

ofpolyaniline

and derivatives

Polyaniline derivatives were synthesized via polycondensations on the basisof Ulmannreactionsbetween1,3or 1,4-dibrombenzene or 1,3,5&ibromobenzeneand 1,3- or 1,4diaminobenzeneby using CuI as a catalyst in nitrobenzene. After 24 hrs, the productswere washedwith THIFandtreatedby diluted HCI under argon atmosphereand then dried in VCICUO. All of the polymerswere infusibleandpartly solublein l-methyl2-pyrrolidone. Syntheticroutesand possiblestructuresof the polymers are showedin Scheme1. We also synthesizeda solublepolyaniline derivative substitutedwith a dodecyl group usingthe samemethodto confii the correspondingmolecular structure. 2-2.

Synthesis ofpolyaminopyridine

derivative

with

PmAPY

(poly-m-aminopyridine)

stable radical PmAPYO(poly-m-aminopyridine

Polyaniline derivative with a stable radical precursor, poly(4,4’-diphenylamine-3,5-di-tert-butyl-4-hydroxy benzylidene) [PDDB], wassynthesizedwith a dehydrativepolycondensation by 0379-6779/97/S17.00 0 1997 Elsevier PII SO379-6779(96)04550-X

k

(poly-m&aniline)

den’vative

Poly-m-aminopyridine (PmAPY) was synthesized via polycondensation on the basisof Ulmann reactionbetween2,6diaminopyridineand 2,6-dibromopyridineby using CuI as a catalyst in nitrobenzene. PmAPY was oxidized with 3chloroperbenzoicacid for 24 hrs to give a polyaminopyridine oxide (PmAPYO), asalsoshownin Scheme1. 2-3. Synthesis of polyaniline gro*P

k Pm&AN

Science S.A. Ail rights reserved

oxide)

t,

Scheme1. Synthesesof polyaniline and polyaminopyridine derivatives

H. Goto et al. /Synthetic

1684

OH

Metals

PDDBO

w

3. Results and discussion IR spectra and electn’cal conductivities

IR spectraof polyanilinederivativesare shownin Fig. 1. IR peaksat 1451cm” and1650cm-’ are assignedto C=C stretching vibrations of benzoid and quinoid structures,respectively. A peak at 1381 cm-’ is assignedto C-N stretching vibration. Absorption intensity due to the quinoid structure of PmAN is relatively small comparedwith that of PpAN, suggestingthat PmANhasa lesssegmentof the quinoidstructure. Furthermore, Pmm’AN has no quinoid segment. Three peaks at lower wavenumberin Pmm ‘AN are attributedto completelymeta-linked sequences. Electrical conductivities of the polymers were relatively low, asshownin Table 1. Benzoid / C-N st.

IL1,),ll”(‘(

4600

1683-16%

OH

Scheme 2. Polymerization and Oxidation of PDDB and dried in vucuo. Subsequently the polymer was oxidized with PbOz to yield a PDDBO. The color of the polymer changed from olive-green to dark red upon the oxidation.

3-1.

85 (1997)

1

3000 2000 Wavenumber

1000 (cm-l )

W&err$h

(r-in)

Fig. 2. UV-Vis spectraof PDDB andPDDBO ESR spectrumof PDDBO showednot only a signalwith g value of 2.007, but alsotwo so-called“half-field” signalswith g value of 4.000 and 4.250, as describedin Figure 3. Thesehalf-field signals gradually decreasedin intensity with an increaseof temperaturefrom 5 K to 50 K, andthen disappeared above60 K. The half-field signals are due to the inherently forbidden transitionsof A m = f2, i.e., h v = g,BHo = Zg,BH,

H =Ho/2,

wherethe resonance field (H) is a half of centralfield (HO) for the allowedtransitionof hm, = F 1, Thusthe two half-field signals suggesta coexistenceof two kinds of paramagneticspecieswith triplet stateor an existenceof multiplet state,both of which might arise from intra-chain and/or inter-chain spin interactions. Lastly it is worth noting that both an iodine-dopedPmAPY and the pristine PmAPYO also showeda half-field signalwith g of 4.23 aswell asa signalwith g of “2, evenat highertemperature suchas 110K, indicatinga formationof triplet state. 5K r,-1OK

“’

400

Fig. 1. IR spectraof polyanilinederivatives Table 1. Electricalconductivity (S/cm)of the polymer? polymer plistille P??lANb 1.2 x 10’6 PmAPYb 4.0 x 10” PmAPYOb 2.0 x 10’8 PDDB’ 3.7 x 10.6 PDDBO’ 1.5 x 10” “measured with the four-probe pellet ‘cast film from THF

3-2.

iodine 3.1 x 2.6 X 1.5 x 1.9 x 2.0 x method

color (pristine) doped 10’6 emerald green 1O’6 black 10’8 orange olive-green 10’3 10’3 violet bmeasured in the form

c0

,1M)

I 2ou

Magnetic

3x

Field

400

500

(mT)

Fig. 3. Half-field signalof PDDBO

of pressed

Acknowledgments. The presentstudywassupportedby Grantm-Aid for Scientific Researchfrom Ministry of Education, Culture and Scienceof Japan,and from JapanSociety for the Promotion Science, and the Mitsubishi Foundation, and the SasakawaScientific ResearchGrant from The Japan Science Society.

UV-Vis and ESR measurements

Figure 2 showsUV-Vis spectraof PDDB and its oxidized form, PDDBO. The latter hasan extremelybroadbandcentered at 480 mn, which shouldbe attributedto phenoxy radicalsand/or unpairedelectronsat the nitrogen atomsin PDDBO. In fact,

References [l] J. B. Torrance,S. Oostra,A. Nazzal,Syn.Met., 19 (1987)709. [Z] K. Yoshizawa,K. Tanaka,T. Yamabe,J. Chem.. Whys., 96 (1992)5516.