Benzimidazole acrylonitriles as multifunctional push-pull chromophores: Spectral characterisation, protonation equilibria and nanoaggregation in aqueous solutions

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Vol. 178; pp. 225 - 233
• Main Authors: Horak, Ema, Vianello, Robert, Hranjec, Marijana, Krištafor, Svjetlana, Zamola, Grace Karminski, Steinberg, Ivana Murković
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 05.05.2017
• Subjects: Acrylonitrile - chemistry; Aggregation induced emission (AIE); Animals; Benzimidazole; Benzimidazoles - chemical synthesis; Benzimidazoles - chemistry; Cattle; DNA - chemistry; Fluorescent Dyes - chemistry; Hydrogen-Ion Concentration; pH sensitivity; Polymers - chemistry; Protons; Prototropic equilibrium; Push-pull chromophores; Solutions; Spectrometry, Fluorescence; Water - chemistry; Push-pull chromophores; Aggregation induced emission (AIE); Prototropic equilibrium; pH sensitivity; Benzimidazole
• ISSN: 1386-1425; 1873-3557
• DOI: 10.1016/j.saa.2017.02.011

Heterocyclic donor-π-acceptor molecular systems based on an N,N-dimethylamino phenylacrylonitrile benzimidazole skeleton have been characterised and are proposed for potential use in sensing applications. The benzimidazole moiety introduces a broad spectrum of useful multifunctional properties to the system including electron accepting ability, pH sensitivity and compatibility with biomolecules. The photophysical characterisation of the prototropic forms of these chromophores has been carried out in both solution and on immobilisation in polymer films. The experimental results are further supported by computational determination of pKa values. It is noticed that compound 3 forms nanoaggregates in aqueous solutions with aggregation-induced emission (AIE) at 600nm. All the systems demonstrate spectral pH sensitivity in acidic media which shifts towards near-neutral values upon immobilisation in polymer films or upon aggregation in an aqueous environment (compound 3). The structure-property relationships of these functional chromophores, involving their spectral characteristics, acid-base equilibria, pKa values and aggregation effects have been determined. Potential applications of the molecules as pH and biomolecular sensors are proposed based on their pH sensitivity and AIE properties. [Display omitted] •Benzimidazole based acrylonitriles synthesised as push-pull chromophores.•Compound 3 shows aggregation induced emission (AIE) at 600nm in aqueous solutions.•Structure-property study of pH sensitivity and pKa values of chromophores in aqueous solutions•pH sensitive polymeric materials with the apparent pKa values of around 6