title: Excited state intramolecular proton transfer (ESIPT) from phenol to carbon in selected phenylnaphthols and naphthylphenols.
abstract: ESIPT and solvent-assisted ESPT in isomeric phenyl naphthols and naphthyl phenols 5-8 were investigated by preparative photolyses in CH3CN-D2O, fluorescence spectroscopy, LFP, and ab initio calculations. ESIPT takes place only in 5 (D-exchange Φ = 0.3), whereas 6-8 undergo solvent-assisted PT with much lower efficiencies. The efficiency of the ESIPT and solvent-assisted PT is mainly determined by different populations of the reactive conformers in the ground state and the NEER principle. The D-exchange experiments and calculations using RI-CC2/cc-pVDZ show that 5 in S1 deactivates by direct ESIPT from the OH to the naphthalene position 1 through a conical intersection with S0, delivering QM 14 that was detected by LFP (τ = 26 ± 3 ns). ESIPT to position 3 in 5 is possible but it proceeds from a less-populated conformer and involves an energy barrier on S1. In solvent-assisted PT to naphthalene position 4 in 5, zwitterion 17 is formed, which cyclizes to stable naphthofuran photoproducts 9-12. The regiochemistry of the deuteration in solvent-assisted PT was correlated with the NBO charges of the corresponding phenolates/naphtholates 5(-)-8(-). Combined experimental and theoretical data indicate that solvent-assisted PT takes place via a sequential mechanism involving first deprotonation of the phenol/naphthol, followed by the protonation by H2O in the S1 state of phenolate/naphtholate. The site of protonation by H2O is mostly at the naphthalene α-position.
authors.affiliation: Department of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia. nbasaric@irb.hr
authors.forename: Nikola
authors.initials: N
authors.lastname: Basarić
authors.forename: Nađa
authors.initials: N
authors.lastname: Došlić
authors.forename: Jakov
authors.initials: J
authors.lastname: Ivković
authors.forename: Yu-Hsuan
authors.initials: YH
authors.lastname: Wang
authors.forename: Jelena
authors.initials: J
authors.lastname: Veljković
authors.forename: Kata
authors.initials: K
authors.lastname: Mlinarić-Majerski
authors.forename: Peter
authors.initials: P
authors.lastname: Wan
mesh_terms: D002244:Carbon / Q000737:chemistry*; D009284:Naphthols / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory
chemical_list: D009284:Naphthols; D010636:Phenols; D011522:Protons; D002244:Carbon