Controlled shift in the tautomeric equilibrium of 4-((phenylimino)methyl)naphthalen-1-ol

Solvent control of intramolecular proton transfer: is 4-hydroxy-3-(piperidin-1-ylmethyl)-1-naphthaldehyde a proton crane?

The solvent dependent excited state dynamics of 4-hydroxy-3-(piperidin-1-ylmethyl)-1-naphthaldehyde (compound 2), a candidate for a molecular switch based on intramolecular proton transfer, was investigated by ultrafast spectroscopy and quantum-chemical calculations. In acetonitrile a mixture of molecules in the enol and zwitterionic proton transfer (PT) form exists in the ground state. However, the zwitterion is the energetically favored one in the electronically excited state. Optical excitation of the enol form results in intramolecular proton transfer and formation of the PT form within 1.4 ps. In addition we observe the appearance of a long living species with a rate of 1/(330 ps) which returns to the original ground state on time scales beyond 2 ns and which is attributed to the triplet state. In toluene the enol form is the only observed ground state tautomer, but no light induced proton transfer occurs. Again the long living triplet state is formed, even with a faster rate of 1/(11 ps). In methanol hydrogen bonds between 2 and solvent molecules stabilize strongly the PT form in the ground as well as in the excited state. Also in this case no light induced intramolecular proton transfer was observed but the formation of a long living species was. However, its absorption spectrum is distinctly different from the triplet state seen in acetonitrile and methanol.

10-Hydroxybenzo[h]quinoline: switching between single- and double-well proton transfer through structural modifications

Proton transfer in HBQ and modified compounds was investigated experimentally (steady state absorption and emission spectroscopy, NMR and chemometrics) and theoretically (DFT and TD-DFT M06-2X/TZVP calculations) in ground and excited singlet state.

4-Hydroxy-1-naphthaldehydes: proton transfer or deprotonation

Proton captured/proton lost: in 4-hydroxy-1-naphthaldehyde concentration dependent deprotonation is observed, while when a piperidine unit is attached the proton is captured.

Zwitterionic 1-{(E)-[(2-methyl-phen-yl)iminium-yl]meth-yl}naphthalen-2-olate

The title Schiff base, C₁₈H₁₅NO, crystallizes in its zwitterionic form and an N—H⋯O hydrogen bond closes an S(6) ring. The dihedral angle between the aromatic ring systems is 36.91 (10)°. Weak aromatic π–π stacking occurs in the crystal [minimum centroid–centroid separation = 3.7771 (15) Å].