1,3,5-Triarylpyrazolines — pH-driven off-on-off molecular logic devices based on a “receptor1-fluorophore-spacer-receptor2” format with internal charge transfer (ICT) and photoinduced electron transfer (PET) mechanisms

• Published in: Canadian journal of chemistry Vol. 93; no. 2; pp. 199 - 206
• Format: Journal Article
• Language: English
• Published: Ottawa NRC Research Press 2015; Canadian Science Publishing NRC Research Press
• Subjects: Charge transfer; Chromophores; Electron transfer; Electrons; Excitation; Fluorescence; Format; internal charge transfer; logique ternaire; Methanol; molecular information processing; photoinduced electron transfer; Protonation; Protons; ternary logic; traitement moléculaire l’information; transfert de charge interne; transfert d’électron par photo-induction; triarylpyrazoline
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/cjc-2014-0266

The excited state photophysical properties of the 1,3,5-triarylpyrazolines 1 – 4 were studied in methanol and 1:1 (v/v) methanol–water, as well as 1:4 (v/v) methanol–water and water by fluorescence spectroscopy. The molecules 2 – 4 incorporate a “receptor 1 -fluorophore-spacer-receptor 2 ” format while 1 is a reference compound based on a “fluorophore-receptor 1 ” design. The molecular probes operate according to photoinduced electron transfer (PET) and internal charge transfer (ICT) processes. At basic and neutral pHs, 2 – 4 are essentially nonfluorescent due to PET from the electron-donating dimethylamino moiety appended on the 5-phenyl ring to the excited state of the 1,3,5-triarylpyrazoline fluorophore. At proton concentrations of 10 −3 mol/L, the dimethylamino unit is protonated resulting in a strong blue fluorescence about 460 nm with significant quantum yields up to 0.54. At acid concentrations above 10 −2 mol/L, fluorescence quenching is observed by an ICT mechanism due to protonation of the pyrazoline chromophore. Symmetrical off-on-off fluorescence–pH profiles are observed, spanning six log units with a narrow on window within three pH units. Hence, 2 – 4 are novel examples of ternary photonic pH sensing molecular devices.