Abstract
In this contribution, we have attempted to solve the challenges in theoretically predicting the photophysical properties of 3-hydroxyisonicotinealdehyde in different pH media. Our calculations results demonstrated that in acidic and neutral conditions, the intermolecular hydrogen bonding (Inter-HB) will increase the energy of the dark nπ* state and inhibit the occurrence of excited-state intramolecular proton transfer (ESIPT), leading to emission from the enol form. In alkaline conditions, the existence of phenolate makes the absence of the ESIPT process. Moreover, the strength of Inter-HB between oxyanion and water increases significantly and the formed complex plays an important role in the emission spectra. The increase in fluorescence quantum yield with increasing pH was found to be correlated with the energy difference between nπ* and ππ* states. Our study not only reveals the multiple roles of Inter-HB in inducing the fluorescence of 3-hydroxyisonicotinealdehyde, but also provides theoretical guides for further development of new fluorophores with intense emission in water.
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