title: 1-Naphthol as an ESPT fluorescent molecular probe for sensing thermotropic microenvironmental changes of pluronic F127 in aqueous media.
abstract: Thermotropic microenvironmental changes and the level of hydration in different microenvironments of pluronic F127 (PF127), (PEO106 PPO70 PEO106, average molar mass 13 000) in aqueous media have been studied using 1-naphthol, which is an ESPT fluorescent molecular probe. The appearance of 1-naphthol neutral form fluorescence in aqueous PF127 (10% w/v) solution indicates the ability of 1-naphthol to sense hydrophobic domains in micellar aggregations. There is a marked enhancement of the neutral form fluorescence at and above the gelation temperature (20 °C), which shows that the probe can accurately sense the sol-gel transition. In the temperature range of 10-40 °C, with increase in temperature there is a progressive enhancement of the neutral form fluorescence and the blue shift of the neutral and anionic form fluorescence; a decrease in the deprotonation rate constant (kpt) indicates that the water-polymer interfacial region is progressively dehydrated. Because kpt is related to the availability of proton-accepting water in the microenvironment of 1-naphthol, the reduction of kpt indicates progressive dehydration. The thermotropic response of the I1/I3 vibronic band ratio of pyrene-1-butyric acid fluorescence shows a progressive increase in the non-polarity of the interfacial domain with increasing temperature. The increase in non-polarity and the decrease of the hydration level are strongly correlated.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India. mishra@iitm.ac.in.
authors.forename: Jitendriya
authors.initials: J
authors.lastname: Swain
authors.forename: Ashok Kumar
authors.initials: AK
authors.lastname: Mishra
mesh_terms: D005456:Fluorescent Dyes / Q000032:analysis* / Q000737:chemistry*; D009284:Naphthols / Q000032:analysis* / Q000737:chemistry; D020442:Poloxamer / Q000032:analysis* / Q000737:chemistry; D011522:Protons; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D009284:Naphthols; D011522:Protons; D014867:Water; D020442:Poloxamer; C029350:1-naphthol