Synthesis and spectroscopic properties of ring-fused thiophene bridged push–pull dyes and their application in dye-sensitized solar cells
Introduction
Dye-sensitized solar cells (DSSCs) have attracted considerable research interest in the past decades due to its advantages such as low cost and easy fabrication.1 As one of the key components of DSSC, Ru complex based sensitizers encountered the problems of limited resource and high toxicity, although they hold the highest power conversion for a long time.2 The search for alternative dyes is now ongoing. Metal-free organic dyes with the structure of donor–π–acceptor are considered to be the promising candidate because of their high molar extinction coefficient, easy modification on structure, low cost, and clean to environment.3, 4, 5 In the past 10 years, great progresses have been achieved on organic dye based DSSC.6, 7, 8, 9, 10 Some organic dyes exhibit good conversion efficiency of about 10%11, 12, 13, 14 and even higher.15, 16 Triarylamine and cyanoacrylic acid are most commonly employed as donor and acceptor, respectively, in the design of donor–π–acceptor structure while thiophene and its derivatives are served as π bridge to provide conjugation and enhance light absorbance.
Among the triarylamine derivatives, dimethylfluoreaniline (or bisdimethylfluorenylamino group) was first introduced into DSSC by Ko’s group which brought the combination of high conversion efficiency with excellent light and thermostability.17 A series of novel dyes derived from dimethylfluoreaniline donor part were hence developed.8, 18, 19, 20, 21, 22, 23 Recently we reported a series of push–pull sensitizers in which benzo[c]thiophene and its precursor bicyclo[2.2.2]octadiene (BCOD) ring-fused thiophene have been introduced as π-conjugated spacers, containing dihexyloxy-substituted triphenylamine as the donor and cyanoacrylic acid as the acceptor.24 It was the first time that benzo[c]thiophene and its precursor were applied as π bridge in dyes for DSSC and we found that appropriate extension in π conjugation significantly red-shifted the absorption spectra and enhanced their performance in DSSC. Since dimethyl-fluoreaniline exhibited excellent performance as donor part of DSSC dyes, it motivated us to design and synthesis new dyes in combination of dimethylfluoreaniline and ring-fused thiophene, with the aim of enriching the alterations of dyes and finding robust and efficient organic dyes for DSSC.
Section snippets
Experiment
The organic dyes OL7–OL10 were prepared following the synthetic procedure illustrated in Scheme 1. 1 was prepared through Ullmann reaction by aniline coupled with 2-iodo-dimethylfluorene in moderate yield. Compound 3 was achieved by reacting 1 with NBS and then with trimethyl borate. Since benzo[c]thiophene is very unstable, its introduction is achieved through the transformation of appropriate precursor. Previously, Ono’s group has reported the facile synthesis of isothianaphthene oligomers
Spectroscopic properties of the ring-fused thiophene bridged bisdimethylfluorenylamino-based push–pull organic dyes
To inspect the effect of fused ring on thiophene for the spectroscopic properties of these dyes, the electronic absorption spectra of dyes OL7–OL10 were measured in dichloromethane, as shown in Figure 1 and the detailed data were listed in Table 1. All dyes exhibited two peaks with maximum absorption bands mainly located at around 340–370 nm and ranging from 470 to 640 nm, respectively, and the latter could be attributed to the intrinsic charge transfer transition from HOMO to LUMO. The
Conclusions
In summary, we have introduced benzo[c]thiophene and its precursor as π bridge to bisdimethylfluorenylamino-based push–pull organic dyes; their spectroscopic and electrochemical properties have been studied. Fusion with benzene ring on thiophene bridge significantly expands π-conjugation thus red-shift the spectrum response and greatly stabilized the LUMO level of dyes. Dye-sensitized solar cells fabricated with these dyes are measured and moderate power conversion is obtained compared with
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Nos. 20971066, 21021062, 21003130), the National Basic Research Program of China (Nos. 2011CB808704, 2011CBA00700), Program for New Century Excellent Talents in University (No. NCET-08-0272), Grant-in-Aids for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (No. 22350083 to H.Y.), JST, CREST (to H.Y.).
References and notes (28)
- et al.
ChemSusChem
(2011) - et al.
Tetrahedron
(2007) - et al.
Tetrahedron
(2007) - et al.
Tetrahedron
(2009) - et al.
Tetrahedron Lett.
(2002) - et al.
Nature
(1991) - et al.
J. Am. Chem. Soc.
(2005) - et al.
Chem. Rev.
(2010) - et al.
Angew. Chem., Int. Ed.
(2009) - et al.
Curr. Org. Chem.
(2007)
Chem. Mater.
New J. Chem.
Chem. Commun.
ChemSusChem
Cited by (0)
- †
Present address: Graduate School of Material Science, Nara Institute of Science and Technology and CREST, JST 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Japan.