Synthesis, Characterization, and Spectroscopic Investigation of Benzoxazole Conjugated Schiff Bases

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• 作者：Fabiano S. Santos ; Tania M. H. Costa ; Valter Stefani ; Paulo F. B. Gon莽alves ; Rodrigo R. Descalzo ; Edilson V. Benvenutti ; Fabiano S. Rodembusch
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：November 24, 2011
• 年：2011
• 卷：115
• 期：46
• 页码：13390-13398
• 全文大小：1079K
• 年卷期：v.115,no.46(November 24, 2011)
• ISSN：1520-5215

文摘

Two Schiff bases were synthesized by reaction of 2-(4鈥?aminophenyl)benzoxazole derivatives with 4-N,N-diethylaminobenzaldehyde. UV鈥搗isible (UV鈥搗is) and steady-state fluorescence in solution were applied in order to characterize its photophysical behavior. The Schiff bases present absorption in the UV region with fluorescence emission in the blue-green region, with a large Stokes鈥?shift. The UV鈥搗is data indicates that each dye behaves as two different chromophores in solution in the ground state. The fluorescence emission spectra of the dye 5a show that an intramolecular proton transfer (ESIPT) mechanism takes place in the excited state, whereas a twisted internal charge transfer (TICT) state is observed for the dye 5b. Theoretical calculations were performed in order to study the conformation and polarity of the molecules at their ground and excited electronic states. Using density functional theory (DFT) methods at theoretical levels BLYP/Aug-SV(P) for geometry optimizations and B3LYP/6-311++G(2d,p) for single-point energy evaluations, the calculations indicate that the lowest energy conformations are in all cases nonplanar and that the dipole moments of the excited state relaxed structures are much larger than those of the ground state structures, which corroborates the experimental UV鈥搗is absorption results.