title: Unusual Fluorescent Responses of Morpholine-functionalized Fluorescent Probes to pH via Manipulation of BODIPY's HOMO and LUMO Energy Orbitals for Intracellular pH Detection.
abstract: Three uncommon morpholine-based fluorescent probes (A,BandC) for pH were prepared by introducing morpholine residues to BODIPY dyes at 4,4'- and 2,6-positions, respectively. In contrast to morpholine-based fluorescent probes for pH reported in literature, these fluorescent probes display high fluorescence in a basic condition while they exhibit very weak fluorescence in an acidic condition. The theoretical calculation confirmed that morpholine is unable to function as either an electron donor or an electron acceptor to quench the BODIPY fluorescence in the neutral and basic condition via photo-induced electron transfer (PET) mechanism because the LUMO energy of morpholine is higher than those of the BODIPY dyes while its HOMO energy is lower than those of the BODIPY dyes. However, the protonation of tertiary amines of the morpholine residues in an acidic environment leads to fluorescence quenching of the BODIPY dyesviad-PET mechanism. The fluorescence quenching is because the protonation effectively decreases the LUMO energy which locates between the HOMO and LUMO energies of the BODIPY dyes. Fluorescent probeCwith deep-red emission has been successfully used to detect pH changes in mammalian cells.
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Jingtuo
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Mu
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Wafa
authors.initials: W
authors.lastname: Mazi
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Kapil
authors.initials: K
authors.lastname: Adhikari
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Mingxi
authors.initials: M
authors.lastname: Fang
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Fei
authors.initials: F
authors.lastname: Xie
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Loredana
authors.initials: L
authors.lastname: Valenzano
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Tiwari
authors.affiliation: Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China.
authors.forename: Fen-Tair
authors.initials: FT
authors.lastname: Luo
authors.affiliation: Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
authors.forename: Haiying
authors.initials: H
authors.lastname: Liu
keywords: BODIPY dye; Intracellular pH; Morpholine moiety; Photoinduced electron transfer (PET)