title: Excited-state intramolecular proton transfer molecules bearing o-hydroxy analogues of green fluorescent protein chromophore.
abstract: o-Hydroxy analogues, 1a-g, of the green fluorescent protein chromophore have been synthesized. Their structures and electronic properties were investigated by X-ray single-crystal analyses, electrochemistry, and luminescence properties. In solid and nonpolar solvents 1a-g exist mainly as Z conformers that possess a seven-membered-ring hydrogen bond and undergo excited-state intramolecular proton transfer (ESIPT) reactions, resulting in a proton-transfer tautomer emission. Fluorescence upconversion dynamics have revealed a coherent type of ESIPT, followed by a fast vibrational/solvent relaxation (<1 ps) to a twisted (regarding exo-C(5)-C(4)-C(3) bonds) conformation, from which a fast population decay of a few to several tens of picoseconds was resolved in cyclohexane. Accordingly, the proton-transfer tautomer emission intensity is moderate (0.08 in 1e) to weak (∼10(-4) in 1a) in cyclohexane. The stronger intramolecular hydrogen bonding in 1g suppresses the rotation of the aryl-alkene bond, resulting in a high yield of tautomer emission (Φ(f) ≈ 0.2). In the solid state, due to the inhibition of exo-C(5)-C(4)-C(3) rotation, intense tautomer emission with a quantum yield of 0.1-0.9 was obtained for 1a-g. Depending on the electronic donor or acceptor strength of the substituent in either the HOMO or LUMO site, a broad tuning range of the emission from 560 (1g) to 670 nm (1a) has been achieved.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, Republic of China.
authors.forename: Wei-Ti
authors.initials: WT
authors.lastname: Chuang
authors.forename: Cheng-Chih
authors.initials: CC
authors.lastname: Hsieh
authors.forename: Chin-Hung
authors.initials: CH
authors.lastname: Lai
authors.forename: Cheng-Hsuan
authors.initials: CH
authors.lastname: Lai
authors.forename: Chun-Wei
authors.initials: CW
authors.lastname: Shih
authors.forename: Kew-Yu
authors.initials: KY
authors.lastname: Chen
authors.forename: Wen-Yi
authors.initials: WY
authors.lastname: Hung
authors.forename: Yu-Hsiang
authors.initials: YH
authors.lastname: Hsu
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
mesh_terms: D018360:Crystallography, X-Ray; D004563:Electrochemistry; D005456:Fluorescent Dyes / Q000032:analysis / Q000138:chemical synthesis*; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000138:chemical synthesis*; D006860:Hydrogen Bonding; D006900:Hydroxylation; D007477:Ions; D049449:Luminescence; D008956:Models, Chemical; D008968:Molecular Conformation; D057054:Molecular Imaging / Q000379:methods*; D011522:Protons; D012997:Solvents / Q000737:chemistry; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D007477:Ions; D011522:Protons; D012997:Solvents; D049452:Green Fluorescent Proteins