A thieno[3,4-c]pyrrole-4,6-dione-based copolymer for efficient solar cells.

A new low-band-gap thieno[3,4-c]pyrrole-4,6-dione-based copolymer, PBDTTPD, has been designed and synthesized. PBDTTPD is soluble in chloroform or o-dichlorobenzene upon heating and shows a broad absorption in the visible region. The HOMO and LUMO energy levels were estimated to be at -5.56 and -3.75 eV, respectively. These electrochemical measurements fit well with an optical bandgap of 1.8 eV. When blended with PC(71)BM, this polymer demonstrated a power conversion efficiency of 5.5% in a bulk-heterojunction photovoltaic device having an active area of 1.0 cm(2).

Synthesis of new pyridazine-based monomers and related polymers for photovoltaic applications.

New aromatic compounds with a pyridazine core have been synthesized. Four electron-withdrawing monomers have been easily prepared from simple condensation reactions and ring closure procedures. Optimized HOMO, LUMO, and bandgap energy levels have been obtained. The resulting conjugated polymers have been tested in organic solar cells. First studies have revealed power conversion efficiencies up to 0.5% for an active area of 1.0 cm(2) .

New low bandgap dithienylbenzothiadiazole vinylene based copolymers: synthesis and photovoltaic properties.

Two new low-bandgap block copolymers derived from dithienylbenzothiadiazole (DTBT) and different electron-rich functional groups (dioctoxyl benzene and N-octyl-diphenylamine), poly(1,4-dioctoxyl-2,5-divinylbenzene-co-4,7-dithiophene-2'-yl-2,1,3-benzothiadiazole) (PPV-DTBT), poly(3,8-divinyl-N-octyl-diphenylamine-co-4,7-dithiophene-2'-yl-2,1,3-benzothiadiazole) (PDPAV-DTBT), were synthesized by Heck cross-coupling polymerization. PPV-DTBT and PDPAV-DTBT are easily soluble in common organic solvents such as o-dichlorobenzene and chloroform. DSC and TGA results indicate that these copolymers possess good thermal stabilities. PPV-DTBT and PDPAV-DTBT films exhibit broad absorption bands at 300-765 nm (with an optical bandgap of 1.62 eV) and 300-733 nm (with an optical bandgap of 1.69 eV), respectively. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PPV-DTBT were estimated by cyclic voltammetry to be -5.43 and -3.74 eV, respectively, and the HOMO and LUMO of PDPAV-DTBT were -5.37 and -3.7 eV, respectively. Preliminary photovoltaic cells based on the composite structure of ITO/PEDOT: PSS/PPV-DTBT:PCBM (1: 2, w/w)/Al showed an open-circuit voltage of 0.75 V, a power conversion efficiency of 0.6%, and a short circuit current of 1.7 mA · cm(-2) .

Optical detection of DNA and proteins with cationic polythiophenes.

In recent years, intense research has been carried out worldwide with the goal of developing simple, sensitive, and specific detection tools for biomedical applications. Along these lines, we reported in 2002 on cationic polythiophene derivatives able to provide ultrasensitive detection levels and the capability to distinguish perfect matches from oligonucleotides having as little as a single base mismatch. It was shown that the intrinsic fluorescence of the random-coil polymers quenches as a result of the planar, highly conjugated conformation adopted by the polymers when complexed with a single-strand DNA (ssDNA) capture probe but increases again after hybridization with the perfectly matched complementary strand. This change in fluorescence intensity is mainly due to a modification in the delocalization of pi electrons along the carbon chain backbone that occurs when switching between the two conformations. Thus, by monitoring, via the change in fluorescence intensity, the hybridization of the complementary ssDNA target with the "duplex", one could detect as little as 220 complementary target molecules in a 150 microL sample volume (0.36 zmol) in less than 1 hour. Building on this initial concept, we then reported that tagging the DNA probe with a suitable fluorophore dramatically increases the detection sensitivity. This novel molecular system involves the self-assembly of aggregates of duplexes in solution, prior to the introduction of the target, which allows a highly efficient resonance energy transfer (RET) between a "donor" (being the complex formed of the DNA double helix and the polymer chain wrapped around it) and a large number of neighboring "acceptors" (the fluorophores attached to the DNA probes). The massive intrinsic signal amplification (fluorescence chain reaction or FCR) provided by this novel integrated molecular system allows the specific detection of as little as five dsDNA copies in a 3 mL sample volume in only 5 minutes, without the need for prior amplification of the target. Clearly, direct and reliable detection of DNA hybridization without prior PCR amplification or chemical tagging of the genetic target is now possible with this methodology. We have also shown that proteins can be detected following a similar strategy. Impressive results have also been reported by direct and specific staining of targeted proteins. All these features have recently allowed the development of responsive polymeric supports for the detection of DNA and proteins. All these assays that do not require any chemical manipulation of the biological targets or sophisticated experimental procedures should soon lead to major advances in genomics and proteomics.

Reagentless ultrasensitive specific DNA array detection based on responsive polymeric biochips.

Self-assembled molecular structures immobilized on solid substrates and composed of fluorophore-tagged oligonucleotide probes and an optical polymeric transducer were investigated for the trace level detection of DNA target molecules. Rapid and efficient energy transfer between the polymeric transducer and fluorophores within the molecular aggregates leads to a massive intrinsic amplification of the fluorescence signal and to the label-free detection of as little as 300 DNA molecules, with the specificity required for the detection of single-nucleotide mismatches. This capacity for attomolar detection levels while the sensing structures are attached onto solid supports could lead to the development of biochip platforms for fast and simple PCR-free multitarget DNA detection.