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Photophysical and photochemical properties of difluoroboronated 1,3-diketones having the ferrocene moiety studied by steady-state and laser flash photolyses
Accepted Manuscript Title: Photophysical and photochemical properties of difluoroboronated 1,3-diketones having the ferrocene moiety studied by steady-state and laser flash photolyses Author: Yurie Suwa Minoru Yamaji PII: DOI: Reference:
S1010-6030(16)30157-5 http://dx.doi.org/doi:10.1016/j.jphotochem.2016.06.027 JPC 10274
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date: Revised date: Accepted date:
4-3-2016 20-6-2016 21-6-2016
Please cite this article as: Yurie Suwa, Minoru Yamaji, Photophysical and photochemical properties of difluoroboronated 1,3-diketones having the ferrocene moiety studied by steady-state and laser flash photolyses, Journal of Photochemistry and Photobiology A: Chemistry http://dx.doi.org/10.1016/j.jphotochem.2016.06.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Photophysical and photochemical properties of difluoroboronated 1,3-diketones having the ferrocene moiety studied by steady-state and laser flash photolyses Yurie Suwaa, Minoru Yamajib* ##Email##[email protected]##/Email## aEducation Program of Materials and Bioscience, Graduate School of Science and Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan bDivision of Molecular Science, Graduate School of Science and Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan Fax: +81-277-301212. Graphical abstract fx1 Highlights► BF2 compleses of 1,3-diketones having the ferrocene moiety (Fc@Phs) were prepared. ► Fc@Phs show visible colors and no emission in solution. ► No photodecomposition occurred upon photolysis of Fc@Phs in cyclohexane. ► Laser photolysis studies of Fc@Phs revealed no formation of the triplet states. ► Fc@Phs efficiently convert absorbed photon energy to heat. Abstract We synthesized 1,3-diketones having the ferrocene moiety (FcDKPhs) and the corresponding difluoroboronated complexes (Fc@Phs), and investigated the photophysical and photochemical properties in solution by steady-state and laser flash photolyses. FcDKPhs and Fc@Phs had absorption bands with large absorptivities in the UV-region and ones with small absorptivities in the Vis-region, but provided neither fluorescence nor phosphorescence. FcDKPhs decomposed upon exposure to UV-Vis light while Fc@Phs were stable. No transient signals obtained upon laser flash photolysis of FcDKPhs and Fc@Phs demonstrated absence of intersystem crossing to the triplet states. Fc@Phs efficiently convert absorbed photon energy to heat. Keywords: 1,3-Diketone; ferrocene; difluoroboronated complex; laser flash photolysis; steady-state photolysis 1. Introduction It is reported that 1,3-dibenzoylmethane (DBM), a representative of 1,3-diketones, and their derivatives take enol forms as the molecular configuration at room temperature, and that they are non-fluorescent in solution due to the formation of non-chelated enols (NCE) in the excited singlet states [1-3]. The typical isomerism of DBM is shown in Scheme 1. Some of photoirradiated DBMs decompose in solution according to the Norrish Type I mechanism [3]. Once aromatic 1,3-diketones are coordinated to difluoronated boron (BF2), the BF2 complexes of the 1,3-diketones (BF2DK) are emissive in solution and the solid state [4-6].
S1010-6030(16)30157-5 http://dx.doi.org/doi:10.1016/j.jphotochem.2016.06.027 JPC 10274
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date: Revised date: Accepted date:
4-3-2016 20-6-2016 21-6-2016
Please cite this article as: Yurie Suwa, Minoru Yamaji, Photophysical and photochemical properties of difluoroboronated 1,3-diketones having the ferrocene moiety studied by steady-state and laser flash photolyses, Journal of Photochemistry and Photobiology A: Chemistry http://dx.doi.org/10.1016/j.jphotochem.2016.06.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1. Introduction It is reported that 1,3-dibenzoylmethane (DBM), a representative of 1,3-diketones, and their derivatives take enol forms as the molecular configuration at room temperature, and that they are non-fluorescent in solution due to the formation of non-chelated enols (NCE) in the excited singlet states [1-3]. The typical isomerism of DBM is shown in Scheme 1. Some of photoirradiated DBMs decompose in solution according to the Norrish Type I mechanism [3]. Once aromatic 1,3-diketones are coordinated to difluoronated boron (BF2), the BF2 complexes of the 1,3-diketones (BF2DK) are emissive in solution and the solid state [4-6].
1
Changing the arene systems as the chromophores in the BF2DKs enables to tune the fluorescence colors and quantum yields [7]. It seems that the chromophores in BF2DKs play important roles for controlling photophysical and photochemical properties. Ferrocene (Fc) is a well-known metallocene that has cyclopentadienyl ligands and core metal of Fe(II), and has been used as a redox responsive unit owing to the stability, ease of functionalization and well-defined electrochemical properties [8]. Recently, preparation of 4,4difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) conjugated with the Fc moiety, and their chemical and electrochemical properties have been investigated [9-13]. The colors of ferrocenyl BODIPYs in solution are variable upon chemical and electrochemical oxidation [9,13]. Dy- and tri-ads of Fc and the BODIPY cores were studied as electron donor-acceptor systems for understanding the charge-separation mechanisms using ultrafast spectroscopic measurements [11]. However, photochemical and photophysical investigations for ferrocene-conjugated BF2 complexes except BODIPYs are few because variety of the chelating ligands to BF2 is limited [14,15]. To our knowledge, there are no reports on synthetic and photochemical researches of BF2DK having the Fc moiety as the chromophore. In the present communication, we report synthesis of the 1,3-diketones having the Fc moiety and the corresponding BF2DK (FcDKPhs and Fc@Phs, respectively, see Chart 1), and the photochemical and photophysical properties studied by stationary and laser flash photolysis techniques. Fc@Phs were found to be nonluminescent and robust to UV-Vis photoirradiation. FcDKPhs were also nonluminescent, but labile. 2. Experimental The preparation procedures and the NMR data for FcDKPhs and Fc@Phs used in this study and experimental details are deposited in Supplementary data. 3. Result and Discussion Fig. 1 shows absorption spectra of FcDKPhs and Fc@Phs in CHCl3. The absorption spectra have large absorptivities (104 dm3 mol-1 cm-1) due to the π-π* transitions in the UV-region and ones with small absorptivities (103 dm3 mol-1 cm-1) due to metal-to-
2
ligand-charge-transfer (MLCT) transitions originated from the Fc moiety in the Vis-region. The molar absorption coefficients (ε) determined for FcDKPhs and Fc@Phs are listed in Table 1. Appearance of the intense absorption bands in the UVA region indicates that FcDKPhs take enol forms in the ground state. The absorption bands of Fc@Phs were found to undergo red shifts (ca. 20 nm for the the * band and ca. 70 nm for the MLCT band) compared with those of the corresponding FcDKPhs. The MLCT absorption bands of Fc@Phs were found to redshift on introducing the electron withdrawing group (-CF3) at the para-position of the benzene ring as the counter chromophore. The absorption spectra of Fc@Phs in cyclohexane (CH) and acetonitrile (ACN), deposited in Supplementary data as Fig. S1, are similar to those in CHCl3. From these observations, it is inferred that Fc@Phs have little charge-transfer character in the ground state. Fluorescence at 295 K and phosphorescence in a mixture of methylcyclohexane and isopentane (3:1, v/v, MP) at 77 K were absent from FcDKPhs and Fc@Phs, indicating that excited singlet states deactivate via nonradiative processes and chemical reactions. Fig. 2 shows absorption spectral changes upon steady-state photolysis (λ > 290 nm) of FcDKPhs in aerated CH at 295 K. With the lapse of irradiation time, the intensities of the absorption bands at 340 nm decreased. These observations indicate that FcDKPhs are labile to photoirradiation. The decomposition may proceed in the excited singlet state because the absorption spectra changed in aerated solution. The plausible photochemical reactions in the excited singlet states of FcDKPhs are the Norrish Type I and intramolecular electron transfer between the Fc moiety and the 1,3-diketone backbone. The quantum yields for the decomposition were too small to determine from the absorption changes, presumably, less than 10-4. Conversely, we performed steady-state photolysis of Fc@Phs under the same conditions as for FcDKPhs. No changes in the absorption spectra of Fc@Phs were found, indicating that Fc@Phs are stable upon photoirradiation without apparent photochemical reactions. From these facts, it is inferred that coordinating FcDKPhs to the BF2 unit results in an increase of photostability in Fc@Phs.
3
To understand relaxation processes of the excited states in FcDKPhs and Fc@Phs, we performed nanosecond laser flash photolysis. We observed no transient signals in the wavelength region 370 – 640 nm after 100 ns upon 355 nm laser pulsing in the CH solution of FcDKPhs and Fc@Phs. The observed transient spectra are deposited in Supplementary data as Fig. S2. Upon photoexcitation of 1,3-diketones, NCE formation is characteristic in the excited singlet states as shown in Scheme 1 [1-3], but no transient spectra due to the NCE of FcDKPhs were observed in the present study. Based on these experimental facts, no triplet states of FcDKPhs and Fc@Phs would be formed upon photolysis of these compounds. In other words, intersystem crossing from the lowest excited singlet states (S1) to the triplet states is absent. We have confirmed that FcDKPhs and Fc@Phs showed no fluorescence in solution, that FcDKPhs underwent photodecomposition and that no appreciable photochemical reactions in the S1 state were recognized upon steady-state photolysis of Fc@Phs in CH. Consequently, it is plausible that the excited singlet states of FcDKPhs deactivate competitively by decomposition and internal conversion to the ground state whereas those of Fc@Phs relax via internal conversion to the ground state or fast chemical reactions that quench the fluorescence states, eg., intramolecular electron transfer followed by back electron transfer. Fc@Phs prepared in the present work seem to efficiently convert the absorbed light energy to heat, possibly via the internal conversion or chemical reaction pathways. This finding promises Fc@Phs to be potential as efficient UV-Vis absorbers in material applications. 4. Conclusion We synthesized FcDKPhs and Fc@Phs, and studied the photophysical and photochemical properties in solution based on the measurements upon steady-state and laser flash photolyses. FcDKPhs and Fc@Phs had absorption bands with large absorptivities in the UV-region and small ones in the Vis-light region. No emission at 295 and 77 K was observed from FcDKPhs and Fc@Phs. FcDKPhs underwent photodecomposition whereas Fc@Phs were stable to UVVis light exposure. No transient signals obtained upon laser flash photolysis of FcDKPhs and Fc@Phs showed absence of intersystem crossing to the triplet states. Fc@Phs are found to be
4
stable UV-Vis light absorbers functionalized with efficient photo-thermal conversion by coordinating FcDKPhs to the boron atom. Ultrafast spectroscopic studies are necessary for revealing the precise photophysical features including photochemical phenomena in the S1 states of Fc@Phs, which is underway. Acknowledgments This work has been supported by a Grant-in-Aid for Scientific Research (26288032) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japanese Government. References [1] P. Yankov, S. Saltiel, I. Petkov,;1; Photoketonization and excited state relaxation of dibenzoylmethane in non-polar solvents, J. Photochem. Photobiol. A: Chem., 41 (1988) 205214. [2] S. Tobita, J. Ohba, K. Nakagawa, H. Shizuka,;1; Recovery mechanism of the reaction intermediate produced by photoinduced cleavage of the intramolecular hydrogen bond of dibenzoylmethane, J. Photochem. Photobiol. A: Chem., 92 (1995) 61-67. [3] A. Aspée, C. Aliaga, J.C. Scaiano,;1; Transient enol isomers of dibenzoylmethane and avobenzone as efficient hydrogen donors toward a nitroxide pre-fluorescent probe, Photochem. Photobiol., 83 (2007) 481-485. [4] A.G. Mirochnik, E.V. Gukhman, V.E. Karasev, P.A. Zhikhareva,;1; Fluorescence and photochemical properties of crystalline boron difluorides -diketonato, Russ. Chem. Bull., 49 (2000) 1024-1027. [5] K. Ono, K. Yoshikawa, Y. Tsuji, H. Yamaguchi, R. Uozumi, M. Tomura, K. Taga, K. Saito,;1; Synthesis and photoluminescence properties of BF2 complexes with 1,3-diketone ligands, Tetrahedron, 63 (2007) 9354-9358. [6] A. Sakai, M. Tanaka, E. Ohta, Y. Yoshimoto, K. Mizuno, H. Ikeda,;1; White light emission from a single component system: Remarkable concentration effects on the fluorescence of 1,3diaroylmethanatoboron difluoride, Tetrahedron Lett., 53 (2012) 4138-4141. [7] S. Xu, R.E. Evans, T. Liu, G. Zhang, J.N. Demas, C.O. Trindle, C.L. Fraser,;1; Aromatic difluoroboron -diketonate complexes: Effects of -conjugation and media on optical properties, Inorg. Chem., 52 (2013) 3597-3610. [8] S. Barlow, D. O'Hare,;1; Metal−metal interactions in linked metallocenes, Chem. Rev., 97 (1997) 637-670. [9] X. Yin, Y. Li, Y. Li, Y. Zhu, X. Tang, H. Zheng, D. Zhu,;1; Electrochromism based on the charge transfer process in a ferrocene–BODIPY molecule, Tetrahedron, 65 (2009) 8373-8377. [10] R. Ziessel, P. Retailleau, K.J. Elliott, A. Harriman,;1; Boron dipyrrin dyes exhibiting ``push–pull–pull'' electronic signatures, Chem. Eur. J., 15 (2009) 10369-10374. [11] J.-Y. Liu, M.E. El-Khouly, S. Fukuzumi, D.K.P. Ng,;1; Photoinduced electron transfer in a ferrocene–distyryl BODIPY dyad and a ferrocene–distyryl BODIPY–C60 triad, ChemPhysChem, 13 (2012) 2030-2036. [12] E. Ganapathi, S. Madhu, M. Ravikanth,;1; Synthesis and properties of triazole bridged BODIPY-conjugates, Tetrahedron, 70 (2014) 664-671. [13] Y.V. Zatsikha, E. Maligaspe, A.A. Purchel, N.O. Didukh, Y. Wang, Y.P. Kovtun, D.A. Blank, V.N. Nemykin,;1; Tuning electronic structure, redox, and photophysical properties in asymmetric NIR-absorbing organometallic BODIPYs, Inorg. Chem., 54 (2015) 7915-7928. [14] S. Hachiya, T. Inagaki, D. Hashizume, S. Maki, H. Niwa, T. Hirano,;1; Synthesis and fluorescence properties of difluoro[amidopyrazinato-O,N]boron derivatives: A new boroncontaining fluorophore, Tetrahedron Lett., 51 (2010) 1613-1615. [15] S. Baaziz, N. Bellec, Y. Le Gal, R. Kaoua, F. Camerel, S. Bakhta, B. Nedjar-Kolli, T. Roisnel, V. Dorcet, O. Jeannin, D. Lorcy,;1; Difluoroboron complexes of functionalized
5
dehydroacetic acid: Electrochemical and luminescent properties, Tetrahedron, 72 (2016) 464471.
Scheme 1. Isomerization processes of DBM. Chart 1. Molecular structures and abbreviations of 1,3-diketones (left) and BF2DKs (right) used in this study. The keto form is representative for FcDKPhX. Fig. 1 Absorption spectra in CHCl3 at 295 K for FcDKPh ((a), dash), Fc@Ph ((a), solid), FcDKPhCF3 ((b), dash) and Fc@PhCF3 ((b), solid). Fluorescence at 295 K and phosphorescence in a mixture of methylcyclohexane and isopentane (3:1, v/v, MP) at 77 K were absent from FcDKPhs and Fc@Phs. Fig. 2 Absorption spectral changes upon photolysis (λ > 290 nm) of FcDKPh (a) and FcDKPhCF3 (b) in aerated CH at 295 K. Table Table 1. Molar absorption coefficients (ε) of FcDKPhs and Fc@Phs in CHCl3. Compound ε / dm3 mol−1 cm−1 (λabs / nm) FcDKPh
26100(340), 3400 (485)
FcDKPhCF3
20300 (337), 2700 (504)
Fc@Ph
31700 (365), 4700 (555)
Fc@PhCF3
32500 (360), 5300 (570)
TDENDOFDOCTD
6
3. Result and Discussion Fig. 1 shows absorption spectra of FcDKPhs and Fc@Phs in CHCl3. The absorption spectra have large absorptivities (104 dm3 mol-1 cm-1) due to the π-π* transitions in the UV-region and ones with small absorptivities (103 dm3 mol-1 cm-1) due to metal-to-
2
ligand-charge-transfer (MLCT) transitions originated from the Fc moiety in the Vis-region. The molar absorption coefficients (ε) determined for FcDKPhs and Fc@Phs are listed in Table 1. Appearance of the intense absorption bands in the UVA region indicates that FcDKPhs take enol forms in the ground state. The absorption bands of Fc@Phs were found to undergo red shifts (ca. 20 nm for the the * band and ca. 70 nm for the MLCT band) compared with those of the corresponding FcDKPhs. The MLCT absorption bands of Fc@Phs were found to redshift on introducing the electron withdrawing group (-CF3) at the para-position of the benzene ring as the counter chromophore. The absorption spectra of Fc@Phs in cyclohexane (CH) and acetonitrile (ACN), deposited in Supplementary data as Fig. S1, are similar to those in CHCl3. From these observations, it is inferred that Fc@Phs have little charge-transfer character in the ground state. Fluorescence at 295 K and phosphorescence in a mixture of methylcyclohexane and isopentane (3:1, v/v, MP) at 77 K were absent from FcDKPhs and Fc@Phs, indicating that excited singlet states deactivate via nonradiative processes and chemical reactions. Fig. 2 shows absorption spectral changes upon steady-state photolysis (λ > 290 nm) of FcDKPhs in aerated CH at 295 K. With the lapse of irradiation time, the intensities of the absorption bands at 340 nm decreased. These observations indicate that FcDKPhs are labile to photoirradiation. The decomposition may proceed in the excited singlet state because the absorption spectra changed in aerated solution. The plausible photochemical reactions in the excited singlet states of FcDKPhs are the Norrish Type I and intramolecular electron transfer between the Fc moiety and the 1,3-diketone backbone. The quantum yields for the decomposition were too small to determine from the absorption changes, presumably, less than 10-4. Conversely, we performed steady-state photolysis of Fc@Phs under the same conditions as for FcDKPhs. No changes in the absorption spectra of Fc@Phs were found, indicating that Fc@Phs are stable upon photoirradiation without apparent photochemical reactions. From these facts, it is inferred that coordinating FcDKPhs to the BF2 unit results in an increase of photostability in Fc@Phs.
3
To understand relaxation processes of the excited states in FcDKPhs and Fc@Phs, we performed nanosecond laser flash photolysis. We observed no transient signals in the wavelength region 370 – 640 nm after 100 ns upon 355 nm laser pulsing in the CH solution of FcDKPhs and Fc@Phs. The observed transient spectra are deposited in Supplementary data as Fig. S2. Upon photoexcitation of 1,3-diketones, NCE formation is characteristic in the excited singlet states as shown in Scheme 1 [1-3], but no transient spectra due to the NCE of FcDKPhs were observed in the present study. Based on these experimental facts, no triplet states of FcDKPhs and Fc@Phs would be formed upon photolysis of these compounds. In other words, intersystem crossing from the lowest excited singlet states (S1) to the triplet states is absent. We have confirmed that FcDKPhs and Fc@Phs showed no fluorescence in solution, that FcDKPhs underwent photodecomposition and that no appreciable photochemical reactions in the S1 state were recognized upon steady-state photolysis of Fc@Phs in CH. Consequently, it is plausible that the excited singlet states of FcDKPhs deactivate competitively by decomposition and internal conversion to the ground state whereas those of Fc@Phs relax via internal conversion to the ground state or fast chemical reactions that quench the fluorescence states, eg., intramolecular electron transfer followed by back electron transfer. Fc@Phs prepared in the present work seem to efficiently convert the absorbed light energy to heat, possibly via the internal conversion or chemical reaction pathways. This finding promises Fc@Phs to be potential as efficient UV-Vis absorbers in material applications. 4. Conclusion We synthesized FcDKPhs and Fc@Phs, and studied the photophysical and photochemical properties in solution based on the measurements upon steady-state and laser flash photolyses. FcDKPhs and Fc@Phs had absorption bands with large absorptivities in the UV-region and small ones in the Vis-light region. No emission at 295 and 77 K was observed from FcDKPhs and Fc@Phs. FcDKPhs underwent photodecomposition whereas Fc@Phs were stable to UVVis light exposure. No transient signals obtained upon laser flash photolysis of FcDKPhs and Fc@Phs showed absence of intersystem crossing to the triplet states. Fc@Phs are found to be
4
stable UV-Vis light absorbers functionalized with efficient photo-thermal conversion by coordinating FcDKPhs to the boron atom. Ultrafast spectroscopic studies are necessary for revealing the precise photophysical features including photochemical phenomena in the S1 states of Fc@Phs, which is underway. Acknowledgments This work has been supported by a Grant-in-Aid for Scientific Research (26288032) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japanese Government. References [1] P. Yankov, S. Saltiel, I. Petkov,;1; Photoketonization and excited state relaxation of dibenzoylmethane in non-polar solvents, J. Photochem. Photobiol. A: Chem., 41 (1988) 205214. [2] S. Tobita, J. Ohba, K. Nakagawa, H. Shizuka,;1; Recovery mechanism of the reaction intermediate produced by photoinduced cleavage of the intramolecular hydrogen bond of dibenzoylmethane, J. Photochem. Photobiol. A: Chem., 92 (1995) 61-67. [3] A. Aspée, C. Aliaga, J.C. Scaiano,;1; Transient enol isomers of dibenzoylmethane and avobenzone as efficient hydrogen donors toward a nitroxide pre-fluorescent probe, Photochem. Photobiol., 83 (2007) 481-485. [4] A.G. Mirochnik, E.V. Gukhman, V.E. Karasev, P.A. Zhikhareva,;1; Fluorescence and photochemical properties of crystalline boron difluorides -diketonato, Russ. Chem. Bull., 49 (2000) 1024-1027. [5] K. Ono, K. Yoshikawa, Y. Tsuji, H. Yamaguchi, R. Uozumi, M. Tomura, K. Taga, K. Saito,;1; Synthesis and photoluminescence properties of BF2 complexes with 1,3-diketone ligands, Tetrahedron, 63 (2007) 9354-9358. [6] A. Sakai, M. Tanaka, E. Ohta, Y. Yoshimoto, K. Mizuno, H. Ikeda,;1; White light emission from a single component system: Remarkable concentration effects on the fluorescence of 1,3diaroylmethanatoboron difluoride, Tetrahedron Lett., 53 (2012) 4138-4141. [7] S. Xu, R.E. Evans, T. Liu, G. Zhang, J.N. Demas, C.O. Trindle, C.L. Fraser,;1; Aromatic difluoroboron -diketonate complexes: Effects of -conjugation and media on optical properties, Inorg. Chem., 52 (2013) 3597-3610. [8] S. Barlow, D. O'Hare,;1; Metal−metal interactions in linked metallocenes, Chem. Rev., 97 (1997) 637-670. [9] X. Yin, Y. Li, Y. Li, Y. Zhu, X. Tang, H. Zheng, D. Zhu,;1; Electrochromism based on the charge transfer process in a ferrocene–BODIPY molecule, Tetrahedron, 65 (2009) 8373-8377. [10] R. Ziessel, P. Retailleau, K.J. Elliott, A. Harriman,;1; Boron dipyrrin dyes exhibiting ``push–pull–pull'' electronic signatures, Chem. Eur. J., 15 (2009) 10369-10374. [11] J.-Y. Liu, M.E. El-Khouly, S. Fukuzumi, D.K.P. Ng,;1; Photoinduced electron transfer in a ferrocene–distyryl BODIPY dyad and a ferrocene–distyryl BODIPY–C60 triad, ChemPhysChem, 13 (2012) 2030-2036. [12] E. Ganapathi, S. Madhu, M. Ravikanth,;1; Synthesis and properties of triazole bridged BODIPY-conjugates, Tetrahedron, 70 (2014) 664-671. [13] Y.V. Zatsikha, E. Maligaspe, A.A. Purchel, N.O. Didukh, Y. Wang, Y.P. Kovtun, D.A. Blank, V.N. Nemykin,;1; Tuning electronic structure, redox, and photophysical properties in asymmetric NIR-absorbing organometallic BODIPYs, Inorg. Chem., 54 (2015) 7915-7928. [14] S. Hachiya, T. Inagaki, D. Hashizume, S. Maki, H. Niwa, T. Hirano,;1; Synthesis and fluorescence properties of difluoro[amidopyrazinato-O,N]boron derivatives: A new boroncontaining fluorophore, Tetrahedron Lett., 51 (2010) 1613-1615. [15] S. Baaziz, N. Bellec, Y. Le Gal, R. Kaoua, F. Camerel, S. Bakhta, B. Nedjar-Kolli, T. Roisnel, V. Dorcet, O. Jeannin, D. Lorcy,;1; Difluoroboron complexes of functionalized
5
dehydroacetic acid: Electrochemical and luminescent properties, Tetrahedron, 72 (2016) 464471.
Scheme 1. Isomerization processes of DBM. Chart 1. Molecular structures and abbreviations of 1,3-diketones (left) and BF2DKs (right) used in this study. The keto form is representative for FcDKPhX. Fig. 1 Absorption spectra in CHCl3 at 295 K for FcDKPh ((a), dash), Fc@Ph ((a), solid), FcDKPhCF3 ((b), dash) and Fc@PhCF3 ((b), solid). Fluorescence at 295 K and phosphorescence in a mixture of methylcyclohexane and isopentane (3:1, v/v, MP) at 77 K were absent from FcDKPhs and Fc@Phs. Fig. 2 Absorption spectral changes upon photolysis (λ > 290 nm) of FcDKPh (a) and FcDKPhCF3 (b) in aerated CH at 295 K. Table Table 1. Molar absorption coefficients (ε) of FcDKPhs and Fc@Phs in CHCl3. Compound ε / dm3 mol−1 cm−1 (λabs / nm) FcDKPh
26100(340), 3400 (485)
FcDKPhCF3
20300 (337), 2700 (504)
Fc@Ph
31700 (365), 4700 (555)
Fc@PhCF3
32500 (360), 5300 (570)
TDENDOFDOCTD
6
4
stable UV-Vis light absorbers functionalized with efficient photo-thermal conversion by coordinating FcDKPhs to the boron atom. Ultrafast spectroscopic studies are necessary for revealing the precise photophysical features including photochemical phenomena in the S1 states of Fc@Phs, which is underway. Acknowledgments This work has been supported by a Grant-in-Aid for Scientific Research (26288032) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japanese Government. References
5
dehydroacetic acid: Electrochemical and luminescent properties, Tetrahedron, 72 (2016) 464471.
Scheme 1. Isomerization processes of DBM.
Chart 1. Molecular structures and abbreviations of 1,3-diketones (left) and BF2DKs (right) used in this study. The keto form is representative for FcDKPhX.
Fig. 1 Absorption spectra in CHCl3 at 295 K for FcDKPh ((a), dash), Fc@Ph ((a), solid), FcDKPhCF3 ((b), dash) and Fc@PhCF3 ((b), solid). Fluorescence at 295 K and phosphorescence in a mixture of methylcyclohexane and isopentane (3:1, v/v, MP) at 77 K were absent from FcDKPhs and Fc@Phs.
Fig. 2 Absorption spectral changes upon photolysis (λ > 290 nm) of FcDKPh (a) and FcDKPhCF3 (b) in aerated CH at 295 K. Table Table 1. Molar absorption coefficients (ε) of FcDKPhs and Fc@Phs in CHCl3. Compound ε / dm3 mol−1 cm−1 (λabs / nm) FcDKPh