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Excited State Intramolecular Proton Transfer in Julolidine Derivatives: an ab initio Study

Abstract

We study, with \textit{ab initio} tools, a series of recently prepared fluorescent julolidine derivatives, undergoing Excited State Intramolecular Proton Transfer (ESIPT). We show that the computed free energy change in the excited state (ΔGES) can be used to predict the preference between enol or keto emission, as well as potential dual emission. Indeed, the J1 and J3 molecules experimentally show dual emission, consistent with our finding of a small ΔGES. In agreement with experimental outcomes the complexation between the ESIPT centre and BF2 increases the rigidity of the fluorophore and greatly facilitates emission at energies close to the original enol (E*) fluorescence band. The protonation of the imino group also suppresses ESIPT and sole E* emission is predicted. We disclose here that chemical substitution can significantly tune the radiationless deactivation of the enol related to the rotation around the C=N bond of the ESIPT centre. While there is a significant barrier for the experimentally studied compounds we have found a strong correlation between the barrier height and the electron donating strength of the phenyl substituent. Strong donors such as amine facilitate the barrierless non-radiative decay from E* back to ground state, while weak electron donors make the barrier sufficiently high to allow ESIPT. Strong electron accepting groups as NO2 further increase this barrier. This work therefore illustrates the fine interplays necessary to design of dual emitters.

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Publication details

The article was received on 10 Jul 2018, accepted on 13 Sep 2018 and first published on 13 Sep 2018


Article type: Paper
DOI: 10.1039/C8CP04356F
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Excited State Intramolecular Proton Transfer in Julolidine Derivatives: an ab initio Study

    Š. Budzák and D. Jacquemin, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP04356F

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