Combining a strong donor, tris(dodecyloxy)phenyl)-dithieno[3,2-b:2',3'-d]pyrrole, with a strong acceptor, 4,8-dithien-2-yl-2lambda(4)delta(2)-benzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole, has yielded the lowest bandgap, soluble, spray-processable polymer to date. The polymer has access to four different redox states and shows ambipolar behavior in OFETs. Multiple techniques, including transmission/absorption spectroscopy on SWCNTs and reflectance spectroscopy on gold were used to accurately estimate the optical bandgap at 0.5-0.6 eV, which correlates well to theoretical calculations.

A series of highly soluble donor-acceptor (D-A) copolymers containing N-(3,4,5-tri-ndecyloxyphenyl)-dithieno[3,2-b:2 0 ,3 0 -d]pyrrole (DTP) or N-(2-decyltetradecyl)-dithieno[3,2-b:2 0 ,3 0 -d] pyrrole (DTP 0 ) as donor and three different acceptors, 4,7-dithien-2-yl-[2,1,3]-benzothiadiazole, 4,9dithien-2-yl-6,7-di-n-hexyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline and 4,8-dithien-2-yl-2l 4 d 2 -benzo[1,2c;4,5-c 0 ]bis[1,2,5]thiadiazole (BThX, X ¼ BTD, TQHx 2 , BBT, respectively) were synthesized by Stille coupling polymerizations. The optical and electrochemical properties of these copolymers were investigated, along with their use in field-effect transistors and photovoltaic devices. The band gaps (eV) estimated from UV-vis-NIR spectra and electrochemical measurements of the copolymers varied from ca. 1.5-0.5 eV, and were consistent with quantum-chemical estimates extrapolated using density functional theory. Oxidative and reductive spectroelectrochemistry of the copolymers indicated they can be both p-doped and n-doped, and three to four differently colored redox states of the polymers can be accessed through electrochemical oxidation or reduction. The DTP-BThBTD and DTP-BThTQHx 2 copolymers exhibited average field-effect hole mobilities of 1.2 Â 10 À4 and 2.2 Â 10 À3 cm 2 /(Vs), respectively. DTP-BThBBT exhibited ambipolar field-effect characteristics and showed hole and electron mobilities of 1.2 Â 10 À3 and 5.8 Â 10 À4 cm 2 /(Vs), respectively. Bulk heterojunction photovoltaic devices made from blends of the copolymers with 3 0 -phenyl-3 0 H-cyclopropa[1,9](C 60 -I h ) [5,6]fullerene-3 0 -butanoic acid methyl ester (PCBM) (1:3 weight ratio) exhibited average power conversion efficiencies as high as 1.3% under simulated irradiance of 75 mW/cm 2 .

A family of multi-heterocycle donor–acceptor–donor (DAD) telechelic conjugated oligomers designed for two-photon absorption (2PA) and emission in the near-infrared (near-IR) were prepared, and the relationship between their spectral, structural, and electrochemical properties were investigated. These oligomers, based on electron-rich thiophene, phenylene, and 3,4-ethylenedioxythiophene (EDOT) units as donors along with electron-deficient benzothiadiazole or its derivative units as acceptors, have been characterized through linear absorbance and fluorescence measurements, nonlinear absorbance, cyclic voltammetry, and differential pulse voltammetry to demonstrate the evolution of narrow HOMO–LUMO gaps ranging from 1.05 to 1.95 eV, with the oligomers composed of EDOT and benzo[1,2-c,3,4-c′]bis[1,2,5]thiadiazole (BBT) exhibiting the narrowest gap. The absorption maxima ranges from 517 to 846 nm and the fluorescence maxima ranges from 651 to 1088 nm for the different oligomers. Z-scan and two-photon fluorescence were used to measure the frequency degenerate 2PA of the different oligomers. The oligomer’s 2PA cross sections ranged from 900–3500 GM, with the oligomer containing EDOT donor units and a BBT acceptor unit exhibiting the largest 2PA cross section. The use of these oligomers in red to near-IR emitting polymer light-emitting diodes (PLEDs) was demonstrated by blending the soluble emitting oligomers into a suitable host matrix. Energy transfer from the matrix to the emitting oligomer can be achieved, resulting in PLEDs with pure oligomer emission.

Here we report on the synthesis of two novel very low band gap (VLG) donor-acceptor polymers (Eg ≤ 1 eV) and an oligomer based on the thiadiazoloquinoxaline acceptor. Both polymers demonstrate decent ambipolar mobilities, with P1 showing the best performance of ∼10(-2) cm(2) V(-1) s(-1) for p- and n-type operation. These polymers are among the lowest band gap polymers (≲0.7 eV) reported, with a neutral λmax = 1476 nm (P2), which is the farthest red-shifted λmax reported to date for a soluble processable polymer. Very little has been done to characterize the electrochromic aspects of VLG polymers; interestingly, these polymers actually show a bleaching of their neutral absorptions in the near-infrared region and have an electrochromic contrast up to 30% at a switching speed of 3 s.