title: A class of fluorescent heterocyclic dyes revisited: photophysics, structure, and solvent effects.
abstract: The photophysical behavior of a series of 2-methylthio-5-(Z-carbonyl)thieno-[3,4-e]-3,4-dihydro-1,2,3-triazine-4-ones was investigated by absorption and emission spectroscopy in a range of solvents representing a systematic variation in polarity, polarizability, as well as hydrogen bond donating and accepting capabilities. In all the investigated compounds, the heterocyclic 6-membered ring of the chromophore is involved in interactions between electron donor and acceptor substituents on the thiophene ring. Throughout the series, the charge-donating methylthio group is kept constant, while the acceptor (Z-carbonyl) is varied between amide, ester, and ketone functionalities. The fluorescent first electronically excited state is primarily of intramolecular HOMO-LUMO charge transfer character. All members of the series exhibit solvent-dependent photophysics, although the magnitude of the dependence varies with the nature of the acceptor group. In addition to the solvent-sensitive photophysics, the investigated class of compounds shows high thermal and chemical stability. Among this class of heterocyclic dyes, the amide-substituted compound is superior with respect to high quantum yield and lifetime, and also shows the largest change in emission lifetimes and fluorescence quantum yields upon solvent variation (about 5-fold).
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Lianjie
authors.initials: L
authors.lastname: Zhu
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Becker
authors.forename: Lars
authors.initials: L
authors.lastname: Henriksen
authors.forename: Kristine
authors.initials: K
authors.lastname: Kilså
mesh_terms: D005456:Fluorescent Dyes / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D010777:Photochemistry; D012997:Solvents / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013876:Thiophenes / Q000737:chemistry; D014227:Triazines / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D006571:Heterocyclic Compounds; D012997:Solvents; D013876:Thiophenes; D014227:Triazines