Semiconducting Nanotubes by Intrachain Folding Following Macroscopic Assembly of a Naphthalene–Diimide (NDI) Appended Polyurethane

Abstract

This article describes a well-designed supramolecular assembly of a classical polyurethane scaffold containing pendant n-type semiconducting naphthalene− diimide (NDI) chromophores and consequences on excited state dynamics and charge carrier mobilities. A polycondensation reaction between hexamethylene−diisocyanate and a NDI-containing diol in the presence of a chiral "monofunctional impurity" produced the desired polymer (P1) with a predictable degree of polymerization and end-capping by chiral units. In aliphatic hydrocarbons, such as methylcyclohexane (MCH), P1 adopts a folded conformation with appreciably high thermal stability by intrachain H-bonding among the urethane groups as established by solvent, concentration and temperature-dependent FT-IR and 1 H NMR spectroscopy and small angle XRD studies. Folded structure can be further ascertained by the pronounced Cotton effect in MCH owing to the chiral induction by the so-called "sergeant and soldiers" principle from the asymmetric units located only at the chain ends. Intrachain folding facilitates spatial organization of the pendant groups leading to π−π interaction among the neighboring NDI chromophores attached to the same polymer chain resulting in intense green emission in MCH in sharp contrast to the blue-emitting unfolded polymer in benign solvents such as CHCl 3 or THF. P1 in the folded state resembles the organization of classical bolaamphiphile and thus adopts a polymersome-like spherical structure. Upon aging macroscopic gelation can be observed owing to the fusion of these discrete spherical assemblies generating micrometer long multiwall nanotubes as noticed in HRTEM, AFM and fluorescence microscopy images. Transient absorption spectroscopy studies indicate formation of NDI radical anions in the excited state both in unfolded and folded conformation which contribute to their intrinsic electron transporting (n-type) property, as revealed by flash-photolysis timeresolved microwave conductivity (FP-TRMC). Significantly larger electron mobility and longer lifetime of charge carriers were observed for the folded tubular assembly than those for unfolded polymer, likely due to a better delocalization of the chargecarriers in the integrated tubular assembly consisting of stacked NDI arrays inside the multilayer wall.

Aβ17–20 Peptide‐Guided Structuring of Polymeric Conjugates and Their pH‐Triggered Dynamic Response

“…However, FE‐SEM micrographs of the same solution also displayed the presence of large multimolecular composites from spherical to cubical to rod‐like nanostructures (Figure B and Figure S13A, Supporting Information) . Formation of such large composite structures can be engendered due to the multistep aggregation process which involve aggregation, fusion, and then smoothing of the surface of aggregates, and are reported in the literatures (Figure S13B, Supporting Information) . We believe that the existence of above multistep aggregation phenomenon can be attributed to the unfavorable hydrophobic/hydrophilic ratio as well as to the involved secondary interactions induced by amide bonds of each peptidic repeat units and by few of the unfunctionalized free amino groups at pendants terminal.…”

Supramolecular Chirality Issues in Unorthodox Naphthalene Diimide Gelators

“…( R )‐NDI showed a much larger maximum conductivity ( φ ∑ μ ) max of 1.7×10 −5 cm 2 V −1 s −1 and a long carrier lifetime, in which φ and ∑ μ represent photocarrier generation efficiency and the sum of hole/electron mobilities. The observed maximum conductivity value is slightly smaller than those of the previously studied NDI systems by the same method (3.5×10 and 3.3×10 −5 cm 2 V −1 s −1[27] ) but within a comparable range. The contrast of ( φ ∑ μ ) max between ( R )‐NDI and NDI‐2 suggested that the periodic assembly supported by H‐bonding and π–π interaction was indeed important for providing effective charge‐transport pathways.…”

“…Eur.J. 2018, 24,1938 -1946 www.chemeurj.org previously studied NDI systemsb yt he same method (3.5 10 [26] and 3.3 10 À5 cm 2 V À1 s À1 [27] )b ut within ac omparable range. The contrasto f( fAEm) max between (R)-NDIa nd NDI-2 suggested that the periodic assembly supported by H-bonding and p-p interaction was indeed important for providing effective charge-transport pathways.T he TRMC profile of (S)-NDI was also recorded similarly and yieldedt he (fAEm) max of 1.4 10 À5 cm 2 V À1 s À1 that was essentially comparable with the value of (R)-NDI ( Figure S12, Supporting Information).…”

Ferrocene‐Substituted Naphthalenediimide with Broad Absorption and Electron‐Transport Properties in the Segregated‐Stack Structure

“…By combining the above ϕ value and ϕ Σ μ , the electron mobility of Fc‐NDI‐Fc is, at a minimum, 1.4×10 −3 cm 2 V −1 s −1 . This electron mobility is comparable with other NDI π‐systems determined by FP‐TRMC measurements that were carried out under air . The electron mobility was lower in case of bulk Fc‐NDI‐Fc samples (Figure S6, Supporting Information), indicating that the segregated‐stack structure in the crystal facilitated the electron‐transport event through the NDI conduits.…”