Synthesis And Photophysical Property Of Tri-pod BODIPY Fluorescent Compounds Bearing Phenolic Derivatives

In recent 20 years, BODIPY fluorescent(Boron-dipyrromethene dyes) structures have got rapid development among abundant fluorescent dyes. The BODIPY dyes show many excellent properties, such as stable optical properties, higher fluorescence quantum yields etc. Five novel tripod BODIPY fluorescent compounds bearing phenolic derivatives were synthesized based on the corresponding five intermediates obtained from the nucleophilic substitution of cyanuric chloride. All the ten compounds were characterized by MS, 1HNMR, 13 CNMR, IR, and they haven’t been reported so far. In this paper density functional theory(DFT) at the theoretical level of B3LYP/6-31G(d) and time-dependent density functional theory(TD-DFT) methods were carried out prior to the synthesis of these fluorescent dyes to verify the anticipated intramolecular photoinduced electron transfer(PET) effect.First,the appropriate reaction conditions were found through exploring the reaction sequence, reaction temperature, molar ratio and the reaction time.The optimized reaction conditions as follows:(1) DIEA was the better choice as as acid-binder during the process of intermediates X-b synthesis. The displacement order of cyanuric chloride. First, chlorine atom was substituted by phenol, the second chlorine atom was substituted by 4-hydroxybenzaldehyde; and the third substituted position on the triazine structure allows the introduction of phenol derivatives, and then the products X-b were synthesized finally.(2) Proper eluents and purification methods were found for the workup procedure of the intermediate X-b and the synthetic dyes.Next,analyses of the UV-Vis and fluorescence spectra of the dyes obtained in this paper showed that :(1) In the same solvent, the maximum absorption wavelength of the five dyes was the same.And the five kinds of phenolic moieties used in the auxiliary part affected the maximum emission wavelength of the dyes slightly.(2) Relatively lower fluorescence quantum yield of the dye 5 was found, the fluorescence quantum yield was 20.30%. Its fluorescence quantum yield was decreased by about 20% compared with the series of the five fluorescent compounds, due to the process of the efficient intramolecular photoinduced electron transfer(PET), which has achieved the anticipated goal of this paper.Last, the calculations indicated that:(1) At ground state, the HOMO and LUMO of the molecules were located on π and π* orbitals of BODIPY dye.(2) However, at the first exited state, the frontier molecular orbitals for the five dyes revealed that there was ET from the fluorophore to the acceptor unit on excitation, which may induced the intramolecular photoinduced electron transfer effect and lower fluorescence quantum yields.