Conjugated polymers exhibit strong interactions with single-walled carbon nanotubes (SWNTs). These enable the selective dispersion of specific semiconducting SWNTs in organic solvents and polymer-mediated energy transfer to the nanotubes followed by emission in the near-infrared. Conjugated polyelectrolytes with ionic side-chains can add further functionalities to these nanotube/polymer hybrids such as dispersibility in polar solvents (e.g., methanol) and self-doping. Here, we demonstrate and investigate energy transfer from a range of conjugated polymers to preselected (6,5) SWNTs with varying spectral overlap between the optical transitions of the polymer and nanotube. We find evidence for increased backbone planarization of the polymers wrapped around the nanotubes. Furthermore, ambient p-doping of hybrids of anionic conjugated polyelectrolytes and (6,5) SWNTs blocks energy transfer in contrast to cationic polyelectrolytes. By addition of a mild reducing agent, thus removing the p-doping, the energy transfer can be fully restored pointing toward an electron exchange mechanism. The p-doping of nanotube/polyelectrolyte hybrids in air and their doping-dependent emission and charge transport properties also become apparent in water-gated field-effect transistors based on such networks and might be useful for dual-signal sensing applications.

easily processable (e.g., from solution and on flexible substrates), operate at low voltages, have long retention times, allow for a large number of distinguishable conductance states to be programmed, and should be easily readable and erasable in a controlled manner. [4] A wide range of organic semiconductors has been tested and employed for this purpose, often in field-effect transistor structures. [5] The operating mechanism usually depends on photoinduced charge trapping at the interface between the semiconductor and gate dielectric, thus leading to a threshold shift and a large ratio between the channel conductance before and after irradiatio n. [3c,6] A second possible route is mixing the semiconductor with a photochromic molecule that can act as a charge trap in one state but not the other and thus change the effective mobility of the semiconducting layer. [1a,7] A variety of light-switchable molecules were employed in such devices, e.g., diarylethenes or azobenz enes. [1a,8] Another well-known photochromic system is the spiropyran/merocyanine pair. [7d,9] Upon irradiation of spiropyran with ultraviolet (UV) light, its isomer merocyanine is formed. Merocyanine has a much higher dipole moment than spiropyran and due to its more extended π-conjugation absorbs light in the visible range. [9a] Heating as well as excitation with greenyellow light induces the reverse isomerization, which enables repeated switching between the two forms. One desirable application of such optical memory elements is wearable UV dosimeters that can track the total exposure to harmful ultraviolet radiation. [2,10] Practical devices of this kind require mechanical flexibility and low operating voltages. Ideally, these sensors should be blind to visible light and resettable, i.e., reusable. A variety of materials and sensor concepts have been explored in recent years including photoelectric (e.g., ZnO nanowire photodetectors) [11] and again photochromic (e.g., color change of a polyoxometalates) [12] sensors. Among them, mixed networks of single-walled carbon nanotubes (SWNTs) have been tested in photoelectric devices. Kim et al. found an increase of the resistance (by up to 50%) in a two-terminal device with a random network of SWNTs after UV exposure, which was caused by desorption of oxygen and thus decreased p-doping. [13] In general, nanomaterials such Nanohybrids of purified semiconducting single-walled carbon nanotubes and conjugated polymers with attached spiropyran moieties are created as photoresponsive materials for optical memory devices and ultraviolet (UV) light sensors. The hybrids respond to UV light exposure in air with photoisomerization of the spiropyran groups to merocyanine, resulting in significant and persistent p-doping of the nanotubes, as confirmed by photoluminescence quenching and trion emission. The increased carrier concentration after illumination and the inherently high mobility of carbon nanotubes enable an up to two orders of magnitude increased conductivity of the nanotube/polymer hybrid networks in s...

As narrow optical bandgap materials, semiconducting single-walled carbon nanotubes (SWCNTs) are rarely regarded as charge donors in photoinduced charge-transfer (PCT) reactions. However, the unique band structure and unusual exciton dynamics of SWCNTs add more possibilities to the classical PCT mechanism. In this work, we demonstrate PCT from photoexcited semiconducting (6,5) SWCNTs to a wide-bandgap wrapping poly-[(9,9-dioctylfluorenyl-2,7-diyl)- alt -(6,6′)-(2,2′-bipyridine)] (PFO–BPy) via femtosecond transient absorption spectroscopy. By monitoring the spectral dynamics of the SWCNT polaron, we show that charge transfer from photoexcited SWCNTs to PFO–BPy can be driven not only by the energetically favorable E 33 transition but also by the energetically unfavorable E 22 excitation under high pump fluence. This unusual PCT from narrow-bandgap SWCNTs toward a wide-bandgap polymer originates from the up-converted high-energy excitonic state (E 33 or higher) that is promoted by the Auger recombination of excitons and charge carriers in SWCNTs. These insights provide new pathways for charge separation in SWCNT-based photodetectors and photovoltaic cells.

Organic electrochemical transistors (ECTs) are an important building block for bioelectronics. To promote the required ion transport through the active layer, state-of-the-art semiconducting polymers feature hydrophilic ethylene glycol side chains that increase the volumetric capacitance and transconductance of the devices. Here, we apply this concept to polymer-wrapped single-walled carbon nanotubes (SWCNTs) as a high-mobility semiconducting material. We replace the polyfluorene copolymer (PFO-BPy), which is used for selectively dispersing semiconducting (6,5) SWCNTs and contains octyl side chains, by an equivalent polymer with tetraethylene glycol side chains. Aerosol-jet printed networks of these SWCNTs are applied as the active layer in water-gated ECTs. These show high hole mobilities (3−15 cm 2 •V −1 •s −1 ), significantly improved volumetric capacitances and larger transconductances. Thin networks of SWCNTs reach (219 ± 16) F•cm −1 •V −1 •s −1 as the product of mobility and volumetric capacitance. In situ photoluminescence measurements show more efficient quenching of the near-infrared fluorescence for nanotube networks with hydrophilic glycol side chains compared to those with hydrophobic alkyl side chains, thus corroborating more complete charging under bias. Overall, networks of semiconducting SWCNTs with such tailored wrapping polymers provide excellent device performance. Combined with their inherent mechanical flexibility and durability, they constitute a competitive material for bioelectronics.

Networks of semiconducting single-walled carbon nanotubes (SWNTs) can be used as the transducing layer for sensors based on water-gated transistors. To add specific sensing capabilities, SWNTs are often functionalized with...