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Polydithienothiophenes: two new conjugated materials with narrow band gap
S\l~TI#IETIIE liilmr;ALS ELSEVIER
Synthetic
Polydithienotbiophenes
Metals 84 (1997)
249-250
: two new conjugated materials with narrow band gap
Catia Arbizzani a, Marineha Catellani b, M. Grazia Cerroni ‘, Marina Mastragostino ’ a Diprtimento di Chimica “G. Ciamician”, Via F. Selmi 2, 40126 Bologna, Italy b Istituto di Chimica delle Macromolecole - CNR, Via Bassini 15, 20133 Milano, Italy c Diprtimento di Chimica Fisica, Via Archiraj? 26, 90123 Palermo, Italy
Abstract The electrochemical polymerisation of dithieno[3,4-b:3’,2’-dlthiophene materials with narrow band gap in which the p- and n-doping spectroeleztrochemical study of these polymers is reported. Kqworak
Polydithienothiophenes,
Electrochemical
polymerisation,
1. Introduction
PI. We have previously prepared [3] and electrochemically character&d [4] the low band gap polydithieno[3,4-b:3’,4’dlthiophene (Eg= 1.1 ev). This communication reports the synthesis and the preliminary characterisation of two new materials of polydithienotbiophene family: polydithieno[3,4b:3’,2’-dlthiophene (PDTT2) and polydithieno[3,4b:2’,3’-d] thiophene (PDTIT) . 2. Experimental The monomers, DTT2 and DTF3 (Scheme l), were prepared after de Jong et al. [5]. PDTT2 and PDTI3 films of different thickness were galvanostatically grown on tin oxide (TO) in a&on&rile (ACN), tetraethylammonium tetrafluoborate (Et4NBF4) 0.1 M, the monomer 0.015 M at 1 mA cmw2 with 60 mC crnm2 0379-6779/97/%17.00
Low-bandgap
conjugated polymers, Electrochemical
methods
electrosynthesis charge. All potential values were measured vs. Ag (-140 mV vs. saturated electrode).
The synthesis of new conjugated polymers with low band gap has been receiving considerable attention stimulated by the electronic and electrochemical properties expected for these materials. Conjugated polymers with narrow band gap may show intriusic conductivity as well as both n- and p-doping capacity, along with suitable transparency in the doped states. This opens the possibility in redox supercapacitor and electrochromic window applications . For thiophene based polymers a decrease of the energy gap (Eg) can be obtained increasing the quinoid character of the rceledron conjugated backbone [l], and different approaches have been pursued for the design of narrow band gap materials
PII SO3794779(96)03927-6
and dithieno[3,4-b:2’,3’-dlthiophene leads to conjugated processes are possible in organic electrolytes. The
Q 1997 Elsevier Science S.A. All rights reserved
DTT2 Dithieno[3,4-b:3’,2’-dlthiophene
DTT3 Dtihieno[3,4b:2’,3’-d]thiophene
Scheme 1 3. Characterisation The polymers were investigated by cyclic voltammetry (CV) in both n- and p-doping potential domains in propilenecarbonate (PC) - Et4NBF4 0.2 M. To evince the electronic state variation accompanying the p- and n-doping process, sp&oele&ochemical measurements were performed at the absorption maximum, Imax, on TO/polymer electrodes. Figure 1 shows the cyclic voltabsorbometries (CVAs) superimposed on the CVs in anodic and cathodic domains. The absorbance variation during the process in the cathodic potential range conlirms that the n-doping process is involved in both PDTT2 and PDTl-3. Figure 2 shows the evolution of the electronic absorption spectra of both PDTT2 and PDTT3, in the visible and nearinfrared region, over the p-doping process. The neutral polymers show an absorption band in the visible due to the ‘IIx* transition; during the doping process two bands, due to the charge carriers, appear in the near infrared. The change of the optical properties in the visible region between the neutral
C.Arbizzam et al. /SyntheticMetals 84 (1997) 249-250
250
(blue)and the doped(quite transparent)stateis interesting for applicationsin optical devices. The insetsin figure 2A and2B indicatethe potentialvalue V(V vs. Ag), the p-dopingcharge’Q (in mC cmm2)andthe dopinglevel y% of eachspe&um. Table 1 report the wavelength(Imax> and energy(Em,,) of the absorptionmaximumand energygap(Eg,definedasthe onsetof the opticaltransition) values.
view of their use in symmetricredox supercapacitors and in electrochromicwindows.
e) d)
Table1. Absorptionmaxima and energygap of polymers Polymer Eg@V hmax(nm) Emax PDTT2 PDTT3
650 760
1.91
1.21
1.63
1.12
c) b) 4 I
L
1 pDn2
0.0
A-
1.0
I
2.0
I
3.0
I
4.0
eV
1.2
-1.40
D 4
$ -1.00
4 x 2 iTi
EO.8 s f
c)
i? p.4
-0.60
-
b)
-2.0’0 -2.5
-1.5
-0.5
0.5
20
1.5
'
I
1.80
0.0
“b
V vs Ag 1.0 pDlT3
: 1.0
B
n
I
I
2.0
3.0
i
I
4.0
eV
i 1.40
P 0.0 ii 2 '-1.0 -
L
Figure2. Evolution of the electronicspectraof PDTIX (A) and PD’lT3 (B) in PC-Et4NBF40.2 M over p-dopingprocess.The insetslist the potentialvaluesV at which the electrodeswere charged(in V vs. Ag), the dopingchargeQ (in mC cmm2)and the dopinglevel y%.
-0.60
1 -2.0'
I -2.5
' -1.5
3
' -0:5
*
' 0.5
' 1.5
' 0.20
Acknowledgements: We acknowledgeCNR ProgettoStrategic0 “BatterieLeggereper PAutoElettrica” for financialsupport. References
V vs Ag
Figure 1. CVAs at 50 mV s-l in PC-Et4NBF4 0.2 M of PDTT2 (A) and PDTT3 (B) grown on TO electrodes. Electrical response in the n- andp-dopingdomain(full lines)and optical response at Lax (dottedlines). In conclusion,the absorbancevariation accompanyingthe processin the cathodic domain is comparableto that in the anodicpotential range, and confirmsthat reversiblen-doping processis involved in both PDTT2 and PDDTL. This is an importantfeaturefor applicationin advancedelectrochemical devices. Work is in progressto test the stability of thesepolymersto repeatedcycles, both in p-dopingand n-doping domains,in
[1] J. L. Bredas,J. Chem.Phys. 82 (1985)3808 123M.Kobayashi,N.Colaneri, M.Boysel, F.Wudl, AJ. Heeger,J.Chem.Phys.12 (1985)5717; J. P. Ferraris T. L. Lambert,J. Chem.Sot., Chem.Commun.,(1991) 1268; D. Lorcy, M. P. Cava,Adv. Mat. 4 (1992)563; J.Roncali,C.lIobi*Gautier, Adv. Mat. 6 (1994)846; J. Roncali,C. ThobieGautier, E. H. Elandaloussi, P. F&e, J. Chem.Sot., Chem.Commun.(1994)2249 [3] A. Bolognesi,M. Catellani,S.De&i, R Zamboni C. Taliani,J. Chem.Sot., Chem. Commun.0988) 254 [4] C. Arbizxani, M.Catellani, M. Mastragostino, C. Mingazzini, Electrochim.Acta 40 (1995) 1871 [5] F. De JongandM.G.Janssen, J. Org. Chem.36 (1971) 1645; and J. 0%. Chem.36 (1971) 1998
Synthetic
Polydithienotbiophenes
Metals 84 (1997)
249-250
: two new conjugated materials with narrow band gap
Catia Arbizzani a, Marineha Catellani b, M. Grazia Cerroni ‘, Marina Mastragostino ’ a Diprtimento di Chimica “G. Ciamician”, Via F. Selmi 2, 40126 Bologna, Italy b Istituto di Chimica delle Macromolecole - CNR, Via Bassini 15, 20133 Milano, Italy c Diprtimento di Chimica Fisica, Via Archiraj? 26, 90123 Palermo, Italy
Abstract The electrochemical polymerisation of dithieno[3,4-b:3’,2’-dlthiophene materials with narrow band gap in which the p- and n-doping spectroeleztrochemical study of these polymers is reported. Kqworak
Polydithienothiophenes,
Electrochemical
polymerisation,
1. Introduction
PI. We have previously prepared [3] and electrochemically character&d [4] the low band gap polydithieno[3,4-b:3’,4’dlthiophene (Eg= 1.1 ev). This communication reports the synthesis and the preliminary characterisation of two new materials of polydithienotbiophene family: polydithieno[3,4b:3’,2’-dlthiophene (PDTT2) and polydithieno[3,4b:2’,3’-d] thiophene (PDTIT) . 2. Experimental The monomers, DTT2 and DTF3 (Scheme l), were prepared after de Jong et al. [5]. PDTT2 and PDTI3 films of different thickness were galvanostatically grown on tin oxide (TO) in a&on&rile (ACN), tetraethylammonium tetrafluoborate (Et4NBF4) 0.1 M, the monomer 0.015 M at 1 mA cmw2 with 60 mC crnm2 0379-6779/97/%17.00
Low-bandgap
conjugated polymers, Electrochemical
methods
electrosynthesis charge. All potential values were measured vs. Ag (-140 mV vs. saturated electrode).
The synthesis of new conjugated polymers with low band gap has been receiving considerable attention stimulated by the electronic and electrochemical properties expected for these materials. Conjugated polymers with narrow band gap may show intriusic conductivity as well as both n- and p-doping capacity, along with suitable transparency in the doped states. This opens the possibility in redox supercapacitor and electrochromic window applications . For thiophene based polymers a decrease of the energy gap (Eg) can be obtained increasing the quinoid character of the rceledron conjugated backbone [l], and different approaches have been pursued for the design of narrow band gap materials
PII SO3794779(96)03927-6
and dithieno[3,4-b:2’,3’-dlthiophene leads to conjugated processes are possible in organic electrolytes. The
Q 1997 Elsevier Science S.A. All rights reserved
DTT2 Dithieno[3,4-b:3’,2’-dlthiophene
DTT3 Dtihieno[3,4b:2’,3’-d]thiophene
Scheme 1 3. Characterisation The polymers were investigated by cyclic voltammetry (CV) in both n- and p-doping potential domains in propilenecarbonate (PC) - Et4NBF4 0.2 M. To evince the electronic state variation accompanying the p- and n-doping process, sp&oele&ochemical measurements were performed at the absorption maximum, Imax, on TO/polymer electrodes. Figure 1 shows the cyclic voltabsorbometries (CVAs) superimposed on the CVs in anodic and cathodic domains. The absorbance variation during the process in the cathodic potential range conlirms that the n-doping process is involved in both PDTT2 and PDTl-3. Figure 2 shows the evolution of the electronic absorption spectra of both PDTT2 and PDTT3, in the visible and nearinfrared region, over the p-doping process. The neutral polymers show an absorption band in the visible due to the ‘IIx* transition; during the doping process two bands, due to the charge carriers, appear in the near infrared. The change of the optical properties in the visible region between the neutral
C.Arbizzam et al. /SyntheticMetals 84 (1997) 249-250
250
(blue)and the doped(quite transparent)stateis interesting for applicationsin optical devices. The insetsin figure 2A and2B indicatethe potentialvalue V(V vs. Ag), the p-dopingcharge’Q (in mC cmm2)andthe dopinglevel y% of eachspe&um. Table 1 report the wavelength(Imax> and energy(Em,,) of the absorptionmaximumand energygap(Eg,definedasthe onsetof the opticaltransition) values.
view of their use in symmetricredox supercapacitors and in electrochromicwindows.
e) d)
Table1. Absorptionmaxima and energygap of polymers Polymer Eg@V hmax(nm) Emax PDTT2 PDTT3
650 760
1.91
1.21
1.63
1.12
c) b) 4 I
L
1 pDn2
0.0
A-
1.0
I
2.0
I
3.0
I
4.0
eV
1.2
-1.40
D 4
$ -1.00
4 x 2 iTi
EO.8 s f
c)
i? p.4
-0.60
-
b)
-2.0’0 -2.5
-1.5
-0.5
0.5
20
1.5
'
I
1.80
0.0
“b
V vs Ag 1.0 pDlT3
: 1.0
B
n
I
I
2.0
3.0
i
I
4.0
eV
i 1.40
P 0.0 ii 2 '-1.0 -
L
Figure2. Evolution of the electronicspectraof PDTIX (A) and PD’lT3 (B) in PC-Et4NBF40.2 M over p-dopingprocess.The insetslist the potentialvaluesV at which the electrodeswere charged(in V vs. Ag), the dopingchargeQ (in mC cmm2)and the dopinglevel y%.
-0.60
1 -2.0'
I -2.5
' -1.5
3
' -0:5
*
' 0.5
' 1.5
' 0.20
Acknowledgements: We acknowledgeCNR ProgettoStrategic0 “BatterieLeggereper PAutoElettrica” for financialsupport. References
V vs Ag
Figure 1. CVAs at 50 mV s-l in PC-Et4NBF4 0.2 M of PDTT2 (A) and PDTT3 (B) grown on TO electrodes. Electrical response in the n- andp-dopingdomain(full lines)and optical response at Lax (dottedlines). In conclusion,the absorbancevariation accompanyingthe processin the cathodic domain is comparableto that in the anodicpotential range, and confirmsthat reversiblen-doping processis involved in both PDTT2 and PDDTL. This is an importantfeaturefor applicationin advancedelectrochemical devices. Work is in progressto test the stability of thesepolymersto repeatedcycles, both in p-dopingand n-doping domains,in
[1] J. L. Bredas,J. Chem.Phys. 82 (1985)3808 123M.Kobayashi,N.Colaneri, M.Boysel, F.Wudl, AJ. Heeger,J.Chem.Phys.12 (1985)5717; J. P. Ferraris T. L. Lambert,J. Chem.Sot., Chem.Commun.,(1991) 1268; D. Lorcy, M. P. Cava,Adv. Mat. 4 (1992)563; J.Roncali,C.lIobi*Gautier, Adv. Mat. 6 (1994)846; J. Roncali,C. ThobieGautier, E. H. Elandaloussi, P. F&e, J. Chem.Sot., Chem.Commun.(1994)2249 [3] A. Bolognesi,M. Catellani,S.De&i, R Zamboni C. Taliani,J. Chem.Sot., Chem. Commun.0988) 254 [4] C. Arbizxani, M.Catellani, M. Mastragostino, C. Mingazzini, Electrochim.Acta 40 (1995) 1871 [5] F. De JongandM.G.Janssen, J. Org. Chem.36 (1971) 1645; and J. 0%. Chem.36 (1971) 1998