DOPANT FLEXIBILITY AND PROCESSABILITY STUDIES WITH ELECTRICALLY CONDUCTIVE, FACE-TO-FACE METALLOMACROCYCLIC POLYMERS

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DOPANT FLEXIBILITY AND PROCESSABILITY STUDIES WITH ELECTRICALLY CONDUCTIVE,

FACE-TO-FACE METALLOMACROCYCLIC POLYMERS

T. Inabe, J. Lyding, M. Moguel, T. Marks

To cite this version:

T. Inabe, J. Lyding, M. Moguel, T. Marks. DOPANT FLEXIBILITY AND PROCESS- ABILITY STUDIES WITH ELECTRICALLY CONDUCTIVE, FACE-TO-FACE METALLO- MACROCYCLIC POLYMERS. Journal de Physique Colloques, 1983, 44 (C3), pp.C3-625-C3-631.

�10.1051/jphyscol:19833124�. �jpa-00222635�

J O U R N A L DE PHYSIQUE

Colloque C3, suppl6ment au n06, Tome 44, juin 1983 page C3-625

DOPANT FLEXIBILITY AND PROCESSABILITY STUDIES WITH ELECTRICALLY CONDUCTIVE, FACE-TO-FACE METALLOMACROCYCLIC POLYMERS

T .

habe', J . W . ~ y d i n ~ * , M.K. ~ o ~ u e l ' and T . J . Marks'

Department of chemistry', Department of EZectricaZ Engineering and Computer Science *, and t h e Materials Research center' *, Northwester University, Evanston, I l l i n o i s 60201, U. S. A.

Rdsum'--Dans d e s e x p g r i e n c e s d e dopage avec l a p h t a l o c y a n i n e polymdrisde empilee face-:-face [ s ~ ( P ~ ) o ] ~ , u t i l i s a n t d e s a c c e p t e u r s d 1 6 1 e c t r o n s 1 p o t e n t i e l & l e v 6 (quinone, halogsne au n i t r o s y l e ) , 1 1 h 6 t 6 r o g 6 n 6 i t 6 du procddd d e dopage e t l e m6- canisme d e c o n d u c t i v i t 6 r k s t e n t remarquablement c o n s t a n t s . En u t i l i s a n t d e s t e c h - n i q u e s de f i l a g e humide, nous avons d6montr6 l a p o s s i b i l i t d de pr6pare-r d e s f i b r e s de [ s ~ ( P c ) o ] ~ ( s e u l ou mdlang6 avec l ' a r a m i d e polym6ris6 B h a u t e performance Kevlar) q u i c o n d u i s e n t 1 1 d l e c t r i c i t 6 .

Abstract--In doping e x p e r i m e n t s on t h e c o f a c i a l l y a r r a y e d p h t h a l o c y a n i n e polymer [Si(Pc)O], u s i n g high p o t e n t i a l quinone, halogen, o r n i t r o s y l e l e c t r o n a c c e p t o r s , t h e a c h i e v a b l e degree of p a r t i a l o x i d a t i o n , t h e inhomogeneity of t h e doping p r o c e s s , and t h e c o n d u c t i v i t y mechanism remain remarkably c o n s t a n t . Using wet s p i n n i n g t e c h - n i q u e s , i t h a s proven p o s s i b l e t o p r e p a r e e l e c t r i c a l l y c o n d u c t i v e f i b e r s of

[Si(Pc)O], a l o n e o r blended w i t h t h e h i g h performance aramid polymer Kevlar.

C o v a l e n t l y l i n k i n g s e l e c t e d m o l e c u l a r s u b u n i t s i n t o c o f a c i a l a r r a y s [I-31 n o t o n l y r e p r e s e n t s an e f f e c t i v e approach t o e n f o r c i n g s e g r e g a t e d s t a c k i n g i n "molecular m e t a l s [ 4 ] " but a l s o a r a t i o n a l s y n t h e t i c r o u t e t o whole new f a m i l i e s of e l e c t r i - c a l l y c o n d u c t i v e polymers [ 5 , 6 ] . For t h e m e t a l l o p h t h a l o c y a n i n e s M(Pc)(OH)2, M=Si,Ge, t h e r m a l c o n d e n s a t i o n y i e l d s h i g h l y c r y s t a l l i n e , f a c e - t o - f a c e polymers

[M(Pc)O], ( F i g u r e 1 ) where n ~ 5 0 - 2 0 0 by FT-IR and t r i t i u m end group a n a l y s i s [ T I . Subsequent doping of t h e s e polymers w i t h Br2 and I 2 produces t h e e l e c t r i c a l l y con- d u c t i v e , l i g a n d - o x i d i z e d polymers { [ M ( P C ) O ] B ~ ~ . ~ ) ~ and { [ M ( P C ) O ] I ~ . ~ ) ~ w i t h h i g h a i r and t h e r m a l s t a b i l i t y . We e s t i m a t e t h a t f o r M=Si, t h e e l e c t r i c a l c o n d u c t i v i t y i n t h e polymer c h a i n d i r e c t i o n i s on t h e o r d e r of 100 a-lcm-la We have shown t h a t t h e halogen doping p r o c e s s i s inhomogeneous, and t h a t t h e doped polymers a r e n e a r l y i s o s t r u c t u r a l w i t h t h e "molecular m e t a l " N i ( P c ) I [8-101. The major s t r u c t u r a l d i f - f e r e n c e i s i n t h e r i n g - r i n g i n t e r p l a n a r s p a c i n g , which i n c r e a s e s i n t h e o r d e r : 3.244(2)8, M=Ni; 3.30(2)8, M=Si; 3.48(2)8, M=Ge [81. I m p o r t a n t l y , bandwidth- s e n s i t i v e o p t i c a l , magnetic, and c h a r g e t r a n s p o r t o b s e r v a b l e s can be d i r e c t l y c o r r e - l a t e d w i t h d i f f e r e n c e s i n t h e i n t e r p l a n a r s p a c i n g [8]. Furthermore, from resonance Raman and i o d i n e Mossauer s p e c t r o s c o p y [ I l l , i t can be deduced t h a t halogen i s pre- s e n t predominantly a s Br3- o r 13- i n t h e s e m a t e r i a l s . Hence, t h e d e g r e e of p a r t i a l o x i d a t i o n remains i n t h e r e l a t i v e l y narrow range

0.33-0.36 a s t h e i n t e r p l a n a r s p a c i n g i s v a r i e d by 0.24 8.

I n t h e p r e s e n t c o n t r i b u t i o n , we b r i e f l y d i s c u s s two new a s p e c t s of [M(Pc)O], c h e m i s t r y , p h y s i c s , and polymer s c i e n c e . We i n q u i r e f i r s t whether t h e e n f o r c e d s e g r e g a t e d s t a c k i n g of t h e face-to-face p h t h a l o c y a n i n e a r r a y can y i e l d new i n f o r - mation on t h e n a t u r e of t h e donor-acceptor i n t e r a c t i o n which g i v e s r i s e t o t h e molec- c u l a r m e t a l l i c s t a t e . Next, we a s k whether t h e d i s t i n c t i v e chemical c h a r a c t e r i s t i c s of t h e [M(Pc)OIn s t r u c t u r e w i l l p e r m i t p r o c e s s i n g t e c h n i q u e s ( s p e c i f i c a l l y , f i b e r f a b r i c a t i o n ) which a r e n o t p o s s i b l e w i t h many of t h e o t h e r e l e c t r i c a l l y conductive polymers.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19833124

JOURNAL DE PHYSIQUE

S T R A T E G Y FOR C O N S T R U C T I O N O F C O N D U C T I V E M E T A L L O M A C R O C Y C L I C ARRAYS

1. ASSEMBLY

2. P A R T I A L O X I D A T I O N

Fig. 1 - Scheme for the synthesis of electrically conductive, cofacially joined phthalocyanine polymers.

Fig. 2 - Electrical conductivity as a function of dopant level for polycrystalline

samples of {[Si(Pc)O]DDQy),. DDQ

dichlorodic~anoquinone.

NEW DOPANTS

While i o d i n e o r bromine doping of Ni(Pc) produces a "molecular metal" ( o ( c r y s t a 1 ) ~ 650 ~-'crn-'; powder)

5 5-'cm-l [ 9 ] ) we were s u r p r i s e d t o d i s c o v e r t h a t doping by high p o t e n t i a l o r g a n i c a c c e p t o r s such a s DDQ, TCNQ, c h l o r a n i l , e t c . produces i n s u l a t o r s powder) x 10-~Ci-lcm-~). Does t h i s r e s u l t r e f l e c t a s t r u c t u r a l o r e l e c t r o n i c i n c o m p a t i b i l i t y between t h e donor and a c c e p t o r ? Quinone doping experi- ments on [Si(Pc)OIn, where donor s t a c k i n g i s r i g o r o u s l y e n f o r c e d , a r g u e t h a t i t i s t h e former. I n a l l c a s e s , l a r g e i n c r e a s e s i n [Si(Pc)OIn powder c o n d u c t i v i t i e s a r e measured a f t e r quinone doping. D e t a i l e d s t u d i e s of t h e { [ S ~ ( P C ) O ] D D Q ~ } ~ system r e v e a l a o vs. y p r o f i l e r e m i n i s c e n t of t h e halogen-doped systems ( F i g u r e 2) 181, and a r e s u g g e s t i v e of p e r c o l a t i o n behavior [8,12]. P r e l i m i n a r y d i f f r a c t i o n s t u d i e s i n d i c a t e t h a t t h e DDQ doping i s inhomogeneous. The temperature dependence of { [ S ~ ( P C ) O ] D D Q ~ ) ~ charge t r a n s p o r t ( F i g u r e 3 ) i s a l s o s i m i l a r t o t h a t of t h e

Fig. 3- V a r i a b l e temperature e l e c t r i c a l c o n d u c t i v i t y of p o l y c r y s t a l l i n e { [ S i ( P c ) o J D D Q ~ ) , samples.

{ [ M ( P C ) O ] I ~ ) ~ m a t e r i a l s , and t h e l i n e a r - [ l n ( ~ / o ~ ) ] - ~ vs. T behavior a r g u e s f o r f l u c t u a t i o n - i n d u c e d c a r r i e r t u n n e l l i n g through approximately p a r a b o l i c p o t e n t i a l b a r r i e r s [13,14]. The o p t i c a l p r o p e r t i e s of t h e DDQ-doped face-to-face polymer a r e a l s o compatible with a "molecular metal" i n t h e polymer c h a i n d i r e c t i o n : i n t e n s e e l e c t r o n i c a b s o r p t i o n i n t h e t r a n s m i s s i o n i n f r a r e d spectrum and a plasma-like edge i n t h e i n f r a r e d r e f l e c t i v i t y . I n t e r e s t i n g l y , a l l e f f o r t s t o i n c r e a s e y beyond ca.

0.37 have been unsuccessful. Assuming DDQ i s p r e s e n t a s t h e r a d i c a l a n i o n [ I ] , t h e p l a c e s p i n t h e narrow range observed f o r t h e halogen dopants.

I n a d d i t i o n t o l a r g e , spatially-demanding o r g a n i c dopants, i t was a l s o of

i n t e r e s t t o experiment w i t h a c c e p t o r s having s m a l l e r s p a t i a l demands t h a n Brg- and

13-, t o determine whether c o u n t e r i o n packing e f f e c t s might be d i c t a t i n g t h e maxi-

mum a c h i e v a b l e

value. Doping of [Si(Pc)OIn w i t h NO+BF~- and NO+PF~- proceeds

inhomogeneously, t o y i e l d conductive polymers with maximum dopant s t o i c h i o m e t r i e s

of { [ S ~ ( P C ) O ] ( B F ~ ) ~ , ~ ~ ) ~ and { [ S ~ ( P C ) O I ( P F ~ ) ~ . ~ ~ ) ~ . Thus,

a g a i n remains i n t h e

C3-628 JOURNAL DE PHYSIQUE

halogen doping range. Representative coductivity data for these new materials are shown i n Figures 4 and 5. Again, linear - [ l n ( o / ~ ~ ) ] - ~ vs. T behavior i s observed

Fig. 4 - Variable temperature e l e c t r i c a l conductivity data f o r representative poly- c r y s t a l l i n e samples of { [ S I ( P C ) O ] ( B F ~ ) ~ } ~ .

Fig. 5 - Variable temperature e l e c t r i c a l conductivity data f o r representative

polycrystalline samples of {[Si(PC)O](PF6)y}n.

and i s s u g g e s t i v e of f l u c t u a t i o n - i n d u c e d c a r r i e r t u n n e l l i n g [13,14]. Transmission i n f r a r e d s p e c t r a of t h e s e m a t e r i a l s e x h i b i t s t r o n g e l e c t r o n i c a b s o r p t i o n , and furthermore, an i n f r a r e d plasma-like edge i s seen i n t h e o p t i c a l r e f l e c t i v i t y .

Thus, t h e r e s u l t s of t h e s e [Si(Pc)O], doping s t u d i e s i n d i c a t e t h a t f o r a range of e l e c t r o n a c c e p t o r s d i f f e r i n g g r e a t l y i n s t r u c t u r a l and e l e c t r o n i c c h a r a c t e r - i s t i c s , t h e a c h i e v a b l e degree of p a r t i a l o x i d a t i o n , t h e homogeneity of t h e doping p r o c e s s , and t h e mechanism of charge t r a n s p o r t appear t o be remarkably c o n s t a n t .

PROCESSING

A s u s e f u l m a t e r i a l s , polymers have t r a d i t i o n a l l y o f f e r e d t h e g r e a t a t t r a c t i o n of p r o c e s s a b i l i t y w i t h regard t o forming f i l m s , f o i l s , f i b e r s , molded o b j e c t s , e t c .

[ I S ] . Due t o i n h e r e n t i n s o l u b i l i t y and i n f u s i b i l i t y (not t o mention

a i r - i n s t a b i l i t y ) many of t h e known conductive polymers a r e n o t amenable t o conven- t i o n a l p r o c e s s i n g methodology. That [ S i ( P c ) 0 I n i s chemically very r o b u s t and s o l u b l e i n s t r o n g a c i d s ( t y p i c a l of a phthalocyanine) suggested t h e p o s s i b i l i t y of f i b e r f a b r i c a t i o n by wet s p i n n i n g t e c h n i q u e s [15-171. Such s t u d i e s have been c a r r i e d o u t both with [Si(Pc)O], a l o n e and co-spun a s an " a l l o y " w i t h t h e h i g h modu- l u s aramid f i b e r Kevlar (A) which i s a l s o s o l u b l e i n s t r o n g a c i d s [161. Doping was

Temperature (K)

Fig. 6 - E l e c t r i c a l c o n d u c t i v i t y of an iodine-doped [Si(Pc)Oln f i b e r and t h a t of

a n iodine-doped [Si(Pc)O], powder. The i o d i n e c o n t e n t i s approximately t h e same

f o r t h e two m a t e r i a l s .

C3-630 JOURNAL DE PHYSIQUE

achieved w i t h t h e a c i d s o l v e n t , by t r e a t i n g t h e as-spun f i b e r s w i t h halogen, o r by adding halogen d i r e c t l y t o t h e s p i n n i n g s o l u t i o n p r i o r t o p r e c i p i t a t i o n . The n a t u r e of t h e s e f i b e r s i s p r e s e n t l y under i n t e n s e i n v e s t i g a t i o n . I n F i g u r e s 6 and 7 a r e

(CSi ^(Pc)UJX J : Kevlar

Y

n

Fig. 7 - E l e c t r i c a l c o n d u c t i v i t i e s of f i b e r s o b t a i n e d by co-spinning v a r i o u s pro- p o r t i o n s of [Si(Pc)OIn and Kevlar, followd by halogen doping.

shown p r e l i m i n a r y f o u r - p r o b e v a r i a b l e temperature c o n d u c t i v i t y d a t a f o r doped [Si(Pc)OIn and [Si(Pc)OIn/Kevlar f i b e r s . It can be seen i n F i g u r e 6 t h a t t h e iodine-doped [Si(Pc)OIn f i b e r i s more conductive t h a n t h e corresponding i o d i n e - doped compressed powder. Diminished i n t e r p a r t i c l e c o n t a c t r e s i s t a n c e and/or p r e f e r - e n t i a l alignment of t h e metallomacrocyclic c h a i n s a r e p l a u s i b l e e x p l a n a t i o n s f o r t h i s behavior. The mechanical p r o p e r t i e s of t h e [ S i ( P c ) 0 I n f i b e r s a r e c o n s i d e r a b l y improved by co-spinning with Kevlar. The c o n d u c t i v i t i e s of some of t h e s e blends a s o b t a i n e d from a c i d s o l u t i o n s followed by halogen doping a r e i l l u s t r a t e d i n F i g u r e 7.

It can be seen t h a t t h e f i b e r c o n d u c t i v i t y i n c r e a s e s a s t h e p r o p o r t i o n of phthalo- cyanine polymer i s increased. Questions concerning m i c r o s t r u c t u r e , phase separa- t i o n , and p r e f e r e n t i a l o r i e n t a t i o n a r e p r e s e n t l y under i n v e s t i g a t i o n i n t h e s e i n t e r e s t i n g new m a t e r i a l s .

ACKNOWLEDGMENTS

This r e s e a r c h was generously supported by t h e O f f i c e of Naval Research and by t h e NSF-MRL program through t h e M a t e r i a l s Research Center of Northwestern U n i v e r s i t y

( g r a n t DMR79-23573). J.W.L. t h a n k s IBM Corp. f o r a p o s t d o c t o r a l f e l l o w s h i p . We

thank P r o f e s s o r C . R. Kannewurf f o r h e l p f u l d i s c u s s i o n s .

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