Propeller-shaped bisbenzimidazole wings bearing a naphthalenediimide D-A-D conjugate: crystal structure, solvent-directed nanoscale assembly and fluorimetric detection of picric acid

Kumar, Vivek, Gaur, Ruchi, Ward, Benjamin ORCID: https://orcid.org/0000-0003-1406-5940 and Mishra, Lallan 2026. Propeller-shaped bisbenzimidazole wings bearing a naphthalenediimide D-A-D conjugate: crystal structure, solvent-directed nanoscale assembly and fluorimetric detection of picric acid. Journal of Materials Chemistry C Materials for optical and electronic devices 10.1039/D6TC02701F

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Abstract

Rational control over the aggregation of planar, electron-deficient naphthalenediimide (NDI) chromophores remains challenging, and structural insights into sterically demanding NDI donor–acceptor–donor (D–A–D) architectures are limited. Here, we report the synthesis of BBI–NDI, a novel π-conjugated molecule based on the D–A–D architecture, by coupling an electron-rich propeller having bisbenzimidazole (BBI) as wings with an electron-deficient naphthalenediimide (NDI) core. FT-IR spectroscopy, (1H and 13C) NMR spectroscopy, HRMS, and SC-XRD confirmed its synthesis and structure. In this propeller-shaped structure (triclinic, P1̄), the mean planes of NDI and bis(benzimidazolyl)benzene intersect at 74.23°; the packing is organized by N–H⋯O hydrogen bonds together with C–H⋯π contacts involving lattice DMF and water, and the Hirshfeld surface analysis indicates no effective planar π-stacking. The absorption and emission spectra are solvent-independent, and TD-DFT assigns the observed bands to localized π → π* transitions. The addition of water to DMSO or ethanol solutions drives assembly into morphologically distinct nanostructures—uniform nanospheres (15–25 nm) from DMSO/water and nanoribbons (50–100 nm) from ethanol/water. These nanostructures with opposite trends in emission intensity and lifetime changes are monotonic in DMSO/water (2.29 → 3.58 ns) but non-monotonic in ethanol/water (3.11 → 2.72 → 3.47 ns). In 50% aqueous ethanol, the nanoribbon dispersion responds to picric acid (61.45% quenching) among numerous nitroaromatics and ionic interferents, with a Stern–Volmer constant of 4.12 × 104 M−1 and a detection limit of 0.36 µM. The titration studies (UV-vis, fluorescence and 1H-NMR spectroscopy) indicate that the sensing mechanism is dominated by a static quenching pathway involving ground-state supramolecular complexation (via N–H⋯O/H-bonding). DFT calculations show that the LUMO of PA lies below that of BBI–NDI among the analytes tested, offering a rationale for the observed selectivity and suggesting that a minor contribution through PET cannot be excluded. Recoveries of 90.5–106.5% of PA from river water, sewage and soil extract demonstrate practical utility.

Item Type:	Article
Date Type:	Published Online
Status:	In Press
Schools:	Schools > Chemistry Schools > Physical, Chemical & Environmental Sciences
Publisher:	Royal Society of Chemistry
ISSN:	2050-7526
Date of Acceptance:	1 October 2026
Last Modified:	27 Oct 2026 12:01
URI:	https://orca.cardiff.ac.uk/id/eprint/190412

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