1976
Macromolecules 1993,26, 1975-1979
Preparation of New Redox-Active Quaternized Poly(quino1inium) and Poly(isoquino1inium) Salts Showing Viologen-like Redox Behavior Takaki Kanbara and Takakazu Yamamoto’ Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 227, Japan Received September 14, 1992; Revised Manuscript Received December 18, 1992
ABSTRACT Quaternization of poly(quinoline-4,7-diyl)(P(4,7-Q)) and poly(isoquinoline-l,4-diyl)(P(1,4iQ)) with alkylating reagents (CH30)2SOz, and (CHhCBr) affords the corresponding quaternary poly(quino1inium) and poly(isoquino1inium) salts. The degree of quaternization was in the range -95%. The polymers are electrically conducting, with a conductivity of lP-10-7S cm-l. Quaternized P(4,7-Q) is chemically and electrochemically redox active, and ita cyclic voltammogram shows stable reversible redox peaks at ca. 4 . 5 and 4 . 7 5 V vs SCE, respectively. The color of the polymer changes from pale yellow to dark blue on reduction. On the other hand, quaternized P(1,CiQ) does not give a stable redox cycle, presumably due to the instability of the cation radical formed by the reduction. Weitz-type two-step redox processes similar to those of 1,l’-disubstituted 4,4’-bipyridinium salts account for the redox reaction of quaternized
recently reported quaternization of the quinolineoligomer with alkylating reagents (eq 2).7b
Introduction Since Michaelis first reported on the electrochemical behavior of 1,l’-disubstituted 4,4’-bipyridinium salte (“viologens”),lvarious types of viologens have been prepared and their chemical and electrochemical properties have been extensively investigateda2 Viologens usually show the following Weitz-type two-step redox behaviors.
2, p.2x== +e,
-x
-0,
+x
N
x
-e,
+x
The first-step reduction forms a blue cation radical, and the second-step reduction is considered to form a neutral red quinoid. Due to the interesting redox phenomenaand optical properties of viologens,various polymers containing the viologen structure in the polymer main chain3as well as in pendant groups4 have been synthesized. The polymers have been applied to making modified electrodes3eP as well as p h ~ t o c h r o m i cand ~ ~ -electrochromic ~~
device^.^^.^
Cn,
We recently reported that dehalogenation polycondensation of dihalogenated quinolines and 1,rl-dibromoisoquinoline with zero-valentnickel complexes,which is based on organonickel chemistry? gave various poly(quinolinediyl)s,and poly(isoquinoliie-l,4-diyl)(P(1,44Q)),and poly(quinoline-5,8-diyl) (P(5,8-Q)) and P(1,4-iQ) were converted into electrical conductors on n-type doping.8 n
In contrast to the extensive study of the viologens having the 4,4’-bipyridinium unit, only a few reports on the Weitztype redox behavior of other diquaternary diheterocyclic compoundswith larger r-systems (e.g., 4,4’-biquinolinium d t s and 1,l’-biiiuinoliniumsalts)have beenpublished.5 Especially, much less attention has been paid to polymers with diquaternary diheterocyclic unite in the main chain. These polymers are expected to show redox and optical properties similar to those of viologen units. Three groups, including our group, reported the preparation of poly(4-phenylquinoline-2,6-diyl),6a nonsubstituted quinoline oligomer? and various poly(quinolinediyl)s;8 however, quaternization of the polymers has received only a little attention. Chiang and co-workers 0024-929719312226-1975$04.00/0
x-6-x + +Art
n NI(O)L,
-
+
n NIXsL,
(3)
:
poiy(quino1ine5,Sdiyl)
P(5,8-Q)
poly(quino1ine- poly(isoquinoiine4,7-diyl)
1.4diyl)
P(4,7-Q)
P(1,442)
P(5,8-Q) has only a low solubility in the usual organic solventa, and ita quaternization with alkyl halides is not possible. On the other hand, P(4,7-Q) and P(1,4-iQ) are soluble in chloroform, and their quaternization with alkylating reagents like alkyl halides can be easily carried out in chloroform. Q 1993 American Chemical Society
Macromolecules, Vol. 26, No. 8, 1993
1976 Kanbara and Yamamoto n
x -w+ p
~- 0
1
CHJ = (Cti30)2S0, I C : RX = (CH3),CBr
l a : RX l b : RX
(4)
'
,N
P(4.7-0)
n ca 1 4
m
l+m
6-095
A P ( l 4-\a)
n ca 16
CH3 2
I+m
(b)
The resulting polymers have the diquaternary biquinolinium or biisoquinolinium moieties in the polymer chain, and they are expected to show the Weitz-type two-step redox processes which accompany the color change of the polymer (electrochromism). Since 1and 2 or their reduced forms have a ?r-conjugation system along the polymer chain, they are expected to provide a new class of conductive polymer materials which show viologen-type redox activity. We now report results of the quatemization of the polymers and the chemical and electrochemical properties of the quaternized poly(quino1inium)and poly(isoquinolinium) salts. Results and Discussion Preparation of Quaternized Poly(quinolimium)and Poly(isoquino1inium)Salts. Table I summarizesresults of the quaternization of P(4,7-Q)and P(1,CiQ). As shown in Table I, reaction with iodomethane and dimethylsulfate gives the quaternized polymers in good yields. However, quaternizationof P(4,7-Q)and P(1,4-iQ)withiodoethane, iodopropane, and diethyl sulfate gave only a low degree of quaternization (
