# Decoration of Polyfluorene-Wrapped Carbon Nanotubes with Photoleavable Side-Chains
###### Abstract  
Functionalizing polyfluorene-wrapped carbon nanotubes without damaging their properties is effective via Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC). However, the length and nature of polymer side-chains can impact the conductivity of polyfluorene-SWNT films by preventing close contact between the nanotubes. Here, we investigate the functionalization of a polyfluorene-SWNT complex using photoleavable side-chains that can be removed post-processing. The cleavage of the side-chains containing an ortho-nitrobenzyl ether derivative is efficient when exposed to a UV lamp at 365 nm. The photoisomerization of the \(o\)-nitrobenzyl ether linker into the corresponding \(o\)-nitroobenzaldehyde was first monitored via UV-Vis absorption spectroscopy and \({}^{1}\)H-NMR spectroscopy on the polymer, which showed efficient cleavage after 2 h. We next investigated the cleavage on the polyfluorene-SWNT complex via UV-Vis-NIR absorption spectroscopy. The precipitation of the nanotube dispersion and the broad absorption peaks after overnight irradiation also indicated effective cleavage. In addition, Raman spectroscopy post-irradiation showed that the nanotubes were not damaged upon irradiation. This paper reports a proof of concept that may find applications for SWNT-based materials in which side-chain removal could lead to higher device performance. carbon nanotubes; conjugated polymers; photocleavable sidechains; supramolecular functionalization; click chemistry +
Footnote †: journal: _Molecules_  
selective dispersion of either sc- or m-SWNTs [47; 48; 49; 50], reversible assembly on the nanotube surface [51; 52; 53; 54; 55; 56], or depolymerization in response to a stimulus to release SWNTs [57; 58; 59]. Attention has also been given to conjugated polymers that exhibit reactive functionality post-supramolecular assembly with SWNTs. Specifically, polyfluorene derivatives containing azide groups in the side-chains have been prepared and used to noncovalently functionalize SWNTs [60; 61; 62]. The resulting polyfluorene-SWNTs complexes, dispersed in organic or aqueous solvents, were then functionalized using either Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) or Strain-Promoted Azide-Alkyne Cycloaddition (SPAAC) without damaging SWNTs' optoelectronic properties [60; 61; 62]. However, the introduction of large side-chains that are non-conductive results in a dramatic decrease in conductivity of the polymer-SWNTs complex by preventing good contact between adjacent nanotubes. A potential approach to solve this problem is the use of cleavable side-chains that can be removed after the device's fabrication. In 2019, [PERSON] and coworkers prepared SWNTs thin films dispersed using polythiophene functionalized with carbonate linkers in their side-chains. When heated at 350 \({}^{\circ}\)C, the carbonate linkers were cleaved by decarboxylation resulting in higher conductivity [63]. More recently, our group prepared a polyfluorene-SWNTs complex functionalized with thermally cleavable side-chains that also contain a carbonate linker. The conductivity increased over time upon heating the films at 170 \({}^{\circ}\)C and reached a plateau of (2.0 \(\pm\) 0.1) \(\times\) 10\({}^{-2}\) S/m after 17 h of heating, which was 20 times higher than the non-cleavable sample. This demonstrates the effect of removing the side-chains post processing [64]. Here, we report a different type of cleavable side-chain that contains an ortho-nitrobenzyl (oNB) ether linker. This linker is cleaved when exposed to a 300-365 nm UV light [65; 66]. The cleavage time varies from minutes to a few hours, depending on the intensity of the light, which usually ranges from 1 to 60 mW.cm\({}^{-2}\)[65]. oNB linkers have been widely used as cross-linkers for photodegradable polymers [67], side-chain functionalization [68; 69; 70; 71; 72], solid-phase synthesis [73; 74; 75], photolithography [76; 77], self-immolative polymers [78; 79], and other applications [65; 66; 80; 81].