Unidirectional photoisomerisation in a dual channel proton transfer molecule rhodamine B based Schiff Base: A ratiometric pH sensor

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 459; p. 116027
• Main Authors: Bhakta, Viki, Guchhait, Nikhil
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2025
• Subjects: ESIPT; Fluorescence; pH Sensor; Rhodamine B-based Schiff Base; Rhodamine B-based Schiff Base; Fluorescence; pH Sensor; ESIPT
• ISSN: 1010-6030
• DOI: 10.1016/j.jphotochem.2024.116027

[Display omitted] •Preference of unidirectional photoisomerisation in a judicially designed molecule RHHBO.•Imine Amine isomerisation through six member H-bonded network.•Molecule with ratiometric pH sensor through modulation of fluorescence profile. In this article we have presented the synthesis, characterisation and spectral study of a newly designed fluorophore, (E)-2-((3-(benzo[d]oxazol-2-yl)-5-bromo-2-hydroxybenzylidene)amino)-3′,6′-bis(diethylamino)spiro [isoindoline-1,9′-xanthen]-3-one (RHHBO) which has two possible six member intramolecular hydrogen bonded networks capable for dual channels proton transfer reaction − one towards the N atom of oxazole moiety and the other towards the N atom of rhodamine moity. Details steady state and time resolved spectral analysis of RHHBO and a comparison of spectral features of control compounds 2-(2-hydroxyphenyl)benzoxazole (HBO), (E)-4-bromo-2-(hydrazonomethyl)phenol (HBN) and (E)-2-((5-bromo-2-hydroxybenzylidene)amino)-3′,6′-bis(diethylamino)spiro[isoindoline-1,9′-xanthen]-3-one (RH) having only single proton transfer site reveal that excited state intramolecular proton transfer (ESIPT) in RHHBO occurs towards the rhodamine side but not towards the oxazole side. Interestingly, RHHBO shows different fluorescence colour in acidic and basic medium and hence can be used ratiometric emission based pH sensor.