title: 3,5-Diformylboron dipyrromethenes as fluorescent pH sensors.
abstract: A series of boron dipyrromethene (BODIPY) dyes containing two aldehyde functional groups at the 3 and 5 positions have been synthesized in low-to-decent yields in two steps. In the first step, the meso-aryl dipyrromethanes were treated with POCl(3) in N,N-dimethylformamide to afford 1,9-diformylated dipyrromethanes. In the second step, the diformylated dipyrromethanes were first in situ oxidized with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and then reacted with BF(3)·OEt(2) to afford 3,5-diformylboron dipyrromethenes. The X-ray structural analysis indicated that the aldehyde groups are involved in intramolecular hydrogen bonding with fluoride atoms, which may be responsible for the stability of the diformylated BODIPY compounds. The presence of two formyl groups significantly alters the electronic properties, which is clearly evident in downfield shifts in the (1)H and (19)F NMR spectra, bathochromic shifts in the absorption and fluorescence spectra, better quantum yields, and increased lifetimes compared to 3,5-unsubstituted BODIPYs. Furthermore, 3,5-diformylboron dipyrromethenes are highly electron-deficient and undergo facile reductions compared to unsubstituted BODIPYs. These compounds exhibit pH-dependent on/off fluorescence and thus act as fluorescent pH sensors.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India.
authors.forename: Sheri
authors.initials: S
authors.lastname: Madhu
authors.forename: Malakalapalli Rajeswara
authors.initials: MR
authors.lastname: Rao
authors.forename: Mushtaque S
authors.initials: MS
authors.lastname: Shaikh
authors.forename: Mangalampalli
authors.initials: M
authors.lastname: Ravikanth
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D015374:Biosensing Techniques / Q000379:methods*; D001895:Boron / Q000737:chemistry; D001896:Boron Compounds / Q000138:chemical synthesis* / Q000378:metabolism; D018360:Crystallography, X-Ray; D004126:Dimethylformamide; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000378:metabolism; D005559:Formamides / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011162:Porphobilinogen / Q000031:analogs & derivatives / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D016227:Benzoquinones; D001896:Boron Compounds; D005456:Fluorescent Dyes; D005559:Formamides; D011758:Pyrroles; C512015:dipyrromethane; C507544:dipyrromethene; C000928:dichlorodicyanobenzoquinone; D011162:Porphobilinogen; D004126:Dimethylformamide; D001895:Boron