title: Temperature-dependent fluorescence lifetime of a fluorescent polymeric thermometer, poly(N-isopropylacrylamide), labeled by polarity and hydrogen bonding sensitive 4-sulfamoyl-7-aminobenzofurazan.
abstract: Fluorescent molecular thermometers showing temperature-dependent fluorescence lifetimes enable thermal mapping of small spaces such as a microchannel and a living cell. We report the temperature-dependent fluorescence lifetimes of poly(NIPAM-co-DBD-AA), which is a random copolymer of N-isopropylacrylamide (NIPAM) and an environment-sensitive fluorescent monomer (DBD-AA) containing a 4-sulfamoyl-7-aminobenzofurazan structure. The average fluorescence lifetime of poly(NIPAM-co-DBD-AA) in aqueous solution increased from 4.22 to 14.1 ns with increasing temperature from 30 to 35 degrees C. This drastic change in fluorescence lifetime (27% increase per 1 degrees C) is the sharpest ever reported. Concentration independency, one of the advantages of fluorescence lifetime measurements, was seen in average fluorescence lifetime (13.7 +/- 0.18 ns) of poly(NIPAM-co-DBD-AA) at 33 degrees C over a wide concentration range (0.005-1 w/v%). With increasing temperature, polyNIPAM units in poly(NIPAM-co-DBD-AA) change their structure from an extended form to a globular form, providing apolar and aprotic environments to the fluorescent DBD-AA units. Consequently, the environment-sensitive DBD-AA units translate the local environmental changes into the extension of the fluorescence lifetime. This role of the DBD-AA units was revealed by a study of solvent effects on fluorescence lifetime of a model environment-sensitive fluorophore.
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Gota
authors.forename: Seiichi
authors.initials: S
authors.lastname: Uchiyama
authors.forename: Toshitada
authors.initials: T
authors.lastname: Yoshihara
authors.forename: Seiji
authors.initials: S
authors.lastname: Tobita
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ohwada
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins; D001583:Benzoxazoles / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D006860:Hydrogen Bonding; D015394:Molecular Structure; D010087:Oxides / Q000737:chemistry; D010777:Photochemistry; D011108:Polymers / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012997:Solvents; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: C528280:4-sulfamoyl-7-aminobenzofurazan; D000178:Acrylamides; D000180:Acrylic Resins; D001583:Benzoxazoles; D005456:Fluorescent Dyes; D010087:Oxides; D011108:Polymers; D012997:Solvents; D014867:Water; C052970:poly-N-isopropylacrylamide; D003903:Deuterium