Abstract
Meso-substituted borondipyrromethene (BODIPY)-porphyrin compounds that include free base porphyrin with two different numbers of BODIPY groups (BDP-TTP and 3BDP-TTP) were designed and synthesized to analyze intramolecular energy transfer mechanisms of meso-substituted BODIPY-porphyrin dyads and the effect of the different numbers of BODIPY groups connected to free-base porphyrin on the energy transfer mechanism. Absorption spectra of BODIPY-porphyrin conjugates showed wide absorption features in the visible region, and that is highly valuable to increase light-harvesting efficiency. Fluorescence spectra of the studied compounds proved that BODIPY emission intensity decreased upon the photoexcitation of the BODIPY core, due to the energy transfer from BODIPY unit to porphyrin. In addition, ultrafast pump-probe spectroscopy measurements indicated that the energy transfer of the 3BDP-TTP compound (about 3 ps) is faster than the BDP-TTP compound (about 22 ps). Since the BODIPY core directly binds to the porphyrin unit, rapid energy transfer was seen for both compounds. Thus, the energy transfer rate increased with an increasing number of BODIPY moiety connected to free-base porphyrin.
Highlights
Borondipyrromethene (BODIPY) chromophores have attracted great interest, due to some favorable features such as sharp absorption and emission bands (500 nm), high fluorescence quantum yields and molar absorption coefficients, outstanding chemical photostability, and long excited state lifetimes[1,2,3,4,5]
Double chromophore systems have been studied recently to investigate photoinduced intermolecular electron and/or energy transfer process such as some BODIPY-chromophores which are conjugated to porphyrin [15,21,22,23], pyrene [2,24], rhodamine [25], anthracene [26,27], carbazole [28], and BODIPY [29,30,31,32,33,34]
BODIPYporphyrin conjugates result in a wide range of absorption in the visible region, either covalently or non-covalently bonded, which is highly desirable to increase light-gathering efficiency across the solar spectrum
Summary
Borondipyrromethene (BODIPY) chromophores have attracted great interest, due to some favorable features such as sharp absorption and emission bands (500 nm), high fluorescence quantum yields and molar absorption coefficients, outstanding chemical photostability, and long excited state lifetimes[1,2,3,4,5]. Porphyrins, a group of tetrapyrrolic aromatic macrocycles, demonstrate a strong Soret band in the 400–800 nm region and four intense Q-bands, while metalloporphyrins display a dominant Soret band and one or two Q-bands in the same spectral region They form complex structures with metal ions [35,36,37] and nonmetals [38], they are the most widely investigated chromophores, due to their importance in biochemical processes [39,40,41]. BODIPYporphyrin conjugates result in a wide range of absorption in the visible region, either covalently or non-covalently bonded, which is highly desirable to increase light-gathering efficiency across the solar spectrum Such molecular structures demonstrate efficient and rapid energy transfer from BODIPY to the porphyrin unit in accordance with the type of conjugation and the position of BODIPY. The experimental results of fluorescence, excitation, and ultrafast pump-probe spectroscopy measurements prove the energy transfer from the BODIPY unit to porphyrin
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