New Insight into the Excited-State Proton-Transfer Reactions of 1-Naphthylamine in Solution

Abstract

Proton-transfer reactions from the excited state of 1-naphthylamine (RNH 2 ) have been investigated in aqueous solutions of various HClO 4 concentrations. The system is found to contain three species rather than simply the acidic and the neutral form of RNH 2 as previously believed. The new species X, can be clearly detected at [HClO 4 ] g 5 M, in both absorption and emission. X is proposed to be an adduct of RNH 2 and an unhydrated HClO 4 , i.e., X ≡ RNH 2 ---H + ---ClO 4 -. Absorption and fluorescence spectra of X are shown. Quantum yields of the three excited species RNH 2 *, RNH 3 + *, and X* have been found to be 0.49, 0.327, and 0.065, respectively. A kinetic scheme is presented indicating that the proton transfer from RNH 3 + * depends on the availability of free water, i.e., water that can accept protons. All rate constants have been determined. A theoretical model for the hydration of protons shows that as long as there is excess free water an average of 9 water molecules are used for the hydration of one proton.

Ultrafast excited state proton transfer dynamics of 1,2-dihydroquinolines in methanol solution

“…3-6 Aromatic molecules with acidic proton such as phenols, naphthols, and nitrogen-containing heterocycles are among those showing excited-state intermolecular PT between these compounds and protic solvents. [7][8][9] The enhanced acidity of the excited state assists PT from a solute to a solvent. Intermolecular PT is also observed in H-bonded dimers and bifunctional organic molecules, in which the PT reaction occurs via a bridge of protic solvent molecules.…”

Reaction of spironaphthoxazine with acid

“…The related excitation band was also observed at 350-400 nm when monitoring the 445-nm fluorescence. The 540-nm fluorescence peak is due to MC-H 3 O + These bands, except for the 540-nm fluorescence, are very similar to those of 1-amino-2-naphthol, which exhibits fluorescence and excitation peaks at 357 nm and at 263, 276, 286, and 333 nm, respectively, assigned to the neutral species of 1-amino-2-naphthol [39,40]. Furthermore, the fluorescence peak at around 450 nm and the related excitation band at 350-400 nm are assigned to the anion species.…”

Photophysical Investigation of 8-amino 2-Naphthol in Different Micellar Environment

“…Naphthol and its derivatives have been of considerable interest because of their phototropic behavior in homogeneous and heterogeneous environments. Excited state behavior of naphthol and its derivatives have shown great sensitivity towards surrounding media [23][24][25][26][27][28][29][30]. Substitution of electron withdrawing group at different positions results in remarkable changes in its prototopic behaviours [31][32][33][34].The case of electron donating amino (-NH2) group present at different positions has been studied theoretically as well as experimentally under various pH conditions [35][36][37].…”