Acta Phys. -Chim. Sin. ›› 2010, Vol. 26 ›› Issue (01): 131-140.doi: 10.3866/PKU.WHXB20100118


Excited State Intramolecular Proton Transfer of a Chromophore Linked to Benzotriazole Derivatives

XU Xiao-Fang, GAO Fang, LI Hong-Ru, ZHANG Sheng-Tao   

  1. College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, P. R. China
  • Received:2009-07-22 Revised:2009-10-29 Published:2009-12-29
  • Contact: GAO Fang, LI Hong-Ru;


This paper presents ab initio and density functional theory (DFT) calculations on the excited state intramolecular proton transfer (ESIPT) of a chromophore linked to 2-(2-hydroxyl-phenyl)-benzotriazole: {2-hydroxyl-5-[(p-nitro-styrene)yl-oxymethylene]-phenyl}-(2H-benzotrizole) (C1) and 4'-nitro-3,4-bis-[2-hydroxyl-(2H-benzotrizole)-benzyloxy]-stilbene (C2). We undertook a comprehensive investigation on the ground state and excited state changes of the ESIPT tautomers including their bond lengths, bond angles, Mulliken charges, dipole moments, frontier orbitals, and potential surface curves. A stable keto form (K) was not obtained for C1 in the ground state and a ground state intramolecular proton transfer (GSIPT) was, therefore, impossible. The hydrogen bond strength of the keto form (K*) was higher than that of the enol form(E*) at their excited states. When excited, the negative charge of the hydrogen donor was diminished while the negative charge of the hydrogen acceptor was enhanced. For the excited state of keto from, the electron density moved from a“phenol cycle”to a protonated heterocycle because of the HOMO→LUMO electron transition. A small energy barrier from E* to K*(ca 41 kJ·mol-1) was also observed. These results indicated that the possibility of ESIPT occurring was high for C1. For C2, stable structures for the EK(including keto and enol (E) forms simultaneously), 2K (including two keto forms simultaneously), and 2K* (the excited state of 2K) tautomers could not be obtained because of their high energies. As a consequence, the probability of intramolecular single or double proton transfer at the ground state or excited state intramolecular double proton transfer occurring was negligible. The low transition energy for 2E* (the excited state of 2E)→EK* (the excited state of EK) suggested that an excited state intramolecular single proton transfer was very possible for C2. UV-Vis absorption and fluorescence spectra were calculated and an ESIPT fluorescence emission with a large Stoke's shift was observed.

Key words: Ab initio, Density functional theory, ESIPT, Chromophore, Benzotriazole, Tautomers


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