Non-trivial ground and excited state photophysics of a substituted phenol

5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) shows solvent dependent single or dual emission. The photophysics of 5-tBHI has been studied in a variety of solvents and the results were compared with that of the methyl derivative of the probe as well as the 5-tBHI anion. It has been found that the intramolecular H-bonded conformer of 5-tBHI predominantly exists in non-polar solvents, and undergoes facile excited state intramolecular proton transfer (ESIPT). On the other hand, a dynamic equilibrium can be found in polar, protic solvents, even in the ground state, except in water. NMR analyses confirm the loss of aromaticity of the probe in the ground state via anion formation, in equilibrium with the solvent mediated intermolecularly H-bonded state, in neat polar protic solvents like methanol. The proton transfer process, either intramolecularly or intermolecularly, was found to be of the order of 1 ps, and even faster than the instrumental resolution in the case of water. The current finding provides important insights on the photophysics of this small, substituted phenol. 5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) shows solvent dependent single or dual emission.

Automated summary

5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) exhibits solvent-dependent single or dual emission. The photophysics of 5-tBHI were investigated in different solvents, and compared with the methyl derivative of the probe and the 5-tBHI anion. The results showed that in non-polar solvents, 5-tBHI mainly adopts an intramolecular H-bonded conformer and undergoes excited state intramolecular proton transfer (ESIPT). However, a dynamic equilibrium was observed in polar, protic solvents, except for water. The proton transfer process, whether intramolecular or intermolecular, was found to occur within 1 picosecond.