The effect of intermolecular hydrogen bonding on the photoinduced electron transfer reaction of a naphthalene-triethylamine-alcohol system: Estimation of the equilibrium constant for hydrogen bond formation from fluorescence quenching and reaction pathways

The effect of intermolecular hydrogen bonding on the photophysical and photochemical processes of a naphthalene-triethylamine system in the absence and presence of alcohols was studied. It is shown that the presence of alcohols reduces both the apparent bimolecular rate constant for the quenching of naphthalene fluorescence by triethylamine and the quantum yields of the products in the order 2-methyl-2-propanol < 2-propanol < ethanol < methanol. It is concluded that the hydrogen bonding interaction between the amine and the alcohol suppresses the electron transfer process from triethylamine to the excited singlet state of naphthalene due to the decrease in the concentration of the free amine, and the alcohol acts as a proton donor leading to a strong decrease in the yield of the adduct of naphthalene with triethylamine. The equilibrium constants for the intermolecular hydrogen bonding of triethylamine with alcohols were estimated from the quenching of the naphthalene fluorescence by triethylamine in the absence and presence of alcohols.