Highly Emissive and Electrochemically Stable Thienylene Vinylene Oligomers and Copolymers: An Unusual Effect of Alkylsulfanyl Substituents

Abstract

The synthesis, unexpected efficient photoluminescence, and reversible electrochemical p‐ and n‐doping of new conjugated thienylene vinylene materials functionalized with alkylsulfanyl substituents poly(trithienylene vinylene) (PTTV) and poly(dithienylvinyl‐co‐benzothiadiazole) (PDTVB) along with dithienylvinylene‐based oligomers is reported. The materials are studied by thermal and X‐ray diffraction analysis, optical spectroscopy, cyclic voltammetry, and spectroelectrochemistry. Organic field‐effect transistors (OFETs) are fabricated with PTTV and PDTVB. The polymers, prepared by Stille polycondensation, exhibit good thermal stability and a photoluminescent quantum yield in the range 34%–68%. Low bandgaps (1.5–1.8 eV), estimated by optical and electrochemical measurements along with high stability of both redox states, suggest that these structures are promising materials for photovoltaic applications. OFETs fabricated with PDTVB reveal a hole mobility of 7 × 10−3 cm2 V−1 s−1 with on/off ratio 105, which are comparatively high values for completely amorphous polymer semiconductors.

Tuning the Electronic Properties of Poly(thienothiophene vinylene)s via Alkylsulfanyl and Alkylsulfonyl Substituents

“…A majority of thienylenevinylene oligomers and polymers and their derivatives are almost completely nonemissive. We have earlier reported a dramatic enhancement of fluorescence in thienylene–vinylene oligomers and polymers upon the introduction of sulfanyl side chains, which was unexpected due to the additional sulfur atoms . As a further surprise, we now observed that S-PTTV containing fused thienothiophene rings, is again nonemissive, although the model dimer S-2TTV exhibits a moderate emissivity (λ max = 485 nm, PLQY = 15%, Figure ).…”

“…We have earlier reported a dramatic enhancement of fluorescence in thienylene−vinylene oligomers and polymers upon the introduction of sulfanyl side chains, which was unexpected due to the additional sulfur atoms. 31 As a further surprise, we now observed that S-PTTV containing fused thienothiophene rings, is again nonemissive, although the model dimer S-2TTV exhibits a moderate emissivity (λ max = 485 nm, PLQY = 15%, Figure 4). We could not find a good explanation for these variations, but we note that both alkyl-substituted PTTV (C 6 -PTTV 29 ) and alkylsulfanyl-substituted PTT (SC 8 -PTT, PLQY = 26% 13 ) are reported to show strong photoluminescence.…”

Generation and Recombination Kinetics of Optical Excitations in Poly(3-dodecylthienylenevinylene) with Controlled Regioregularity

“…25,31 Other mechanism such as oxidization of thiophene rings was invoked to explain weak PL in PTV. 32 However, we have measured the PL of fresh and aged PTV-0:10 and found no significant change in terms of both spectra and PLQE. Figure 4b shows the PL of PTV-CR in very dilute dichlorobenzene solution (0.01 mg/mL) and PLQE ∼ 2 Â 10 À4 for PTV-0:10 (regioregular), whereas PLQ E < 10 À5 for PTV-5:5 (regiorandom).…”

“…25,31 Other mechanism such as oxidization of thiophene rings was invoked to explain weak PL in PTV. 32 However, we have measured the PL of fresh and aged PTV-0:10 and found no significant change in terms of both spectra and PLQE.…”

“…Both PL contains one peak (0–0) at 1.27 eV and another peak (0–1) at 1.38 eV, as well as a broad shoulder around 1.52 eV. There is negligible variation of PL with temperature, meaning that nonradiative recombination mechanisms such as phonon emission or disorder/defects/traps do not play an important role, as with most polymers. , Interchain interaction was also not a factor, as in the case of P3HT. , Other mechanism such as oxidization of thiophene rings was invoked to explain weak PL in PTV . However, we have measured the PL of fresh and aged PTV-0:10 and found no significant change in terms of both spectra and PLQE.…”