Modulation of the spectroscopic property of Bodipy derivates through tuning the molecular configuration

Abstract

A series of six Bodipy derivatives, namely 4,4-difluoro-8-(4-amidophenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (1), 4,4-difluoro-8-(4-methylphenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (2), 4,4-difluoro-8-(4-nitrylphenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (3), 4,4-difluoro-8-(4-amidophenyl)-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (4), 4,4-difluoro-8-(4-methylphenyl)-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (5), and 4,4-difluoro-8-(4-nitrylphenyl)-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (6) were structurally characterized by single crystal X-ray diffraction analysis. Two methyl substituents attached at C-1 and C-7 positions of boron-dipyrromethene (Bodipy) moiety in compounds 1-3 were revealed to prevent the free rotation of the benzene moiety, resulting in a molecular configuration with an almost orthogonal dihedral angle between the Bodipy and benzene moieties with the dihedral angle in the range of 81.14-88.56°. This is obviously different from that for 4-6 with a free-rotating benzene moiety relative to the Bodipy core due to the lack of two methyl substituents in the latter series of compounds, leading to an enhanced interaction between the Bodipy and benzene moieties for 4-6 in comparison with 1-3. The resulting larger HOMO-LUMO gap for 1-3 than 4-6 results in a blue-shifted absorption band for 1-3 relative to that for 4-6. Comparative studies over their fluorescence properties also disclose the blue-shifted fluorescence emission band and corresponding higher fluorescence quantum yield for 1-3 relative to those of 4-6, revealing the effect of molecular configuration on the spectroscopic properties of Bodipy derivatives. Comparison of the redox behaviors of these two series of Bodipy compounds provides additional support for this point. In addition, the electron-donating/withdrawing property of the para substituent of the benzene moiety was shown to exhibit a slight influence on the electronic absorption and fluorescence emission properties of the Bodipy compounds.

Coumarin‐3‐Aldehyde as a Scaffold for the Design of Tunable PET‐Modulated Fluorescent Sensors for Neurotransmitters

“…If one compares the quantum yield of the naphthalene derivative ( 1 h ) to the other benzene derivatives (e.g., 1 b ) and the thiophene derivatives (e.g., 2 b ), the sensors in which the C4‐group is more perpendicular, and thereby more rigid, have higher fluorescence quantum yields than those where the C4‐group is more in plane with the coumarin aldehyde scaffold, and thereby less rigid (Figure 3). These results indicate that twisting of the aryl‐fluorophore bond in the excited state leads to nonradiative decay processes and lowers the quantum yield of the fluorophore 12. 13…”

Rationalizing the photophysical properties of BODIPY laser dyes via aromaticity and electron-donor-based structural perturbations

“…The conformation of aryl substituents in the 8-position can also affect photo-excitation, as the interplanar angle dictates the extent to which the p-systems of the BODIPY moiety and the substituent align [26]. This is manifest in the hypsochromic shift in absorption and fluorescence wavelengths observed in BODIPY derivatives, where the rotation of aryl substituents in the 8-position is restricted by methyl groups in the 1-and 7-positions, relative to those with unhindered substituents which are free to align with the BODIPY p-system [27].…”

Effect of the substitution position (2, 3 or 8) on the spectroscopic and photophysical properties of BODIPY dyes with a phenyl, styryl or phenylethynyl group

“…However, the Stokes shifts  are larger than those reported for meso-alkylated and meso-halogenated BODIPY dyes, which are in the 400 cm -1 range. 17,33,40 For instance, meso-p-methylphenyl-3,5-dimethylBODIPY and mesop-methylphenyl-1,3,5,7-tetramethylBODIPYs exhibit  values between 513 and 627 cm -1 , 34 and between 447 and 560 cm -1 for meso-phenyl-3,5-dimethylBODIPY. 33 Concerning the solvent dependence of these spectroscopic parameters, one can observe that while for 3-Ph  , fwhmabs and fwhmem increase more or less parallel with the dielectric constant  of the solvent, this relation is quite erratic for  and fwhmem of 8-Ph.…”

“…32 Another example of the effect of the dihedral angle of the meso-phenyl substituent on the fluorescence properties of the dyes can be found in the comparison between meso-phenyl-3,5-dimethylBODIPY, 33 meso-p-methylphenyl-3,5-dimethylBODIPY and meso-pmethylphenyl-1,3,5,7-tetramethylBODIPY. 34 While the 3,5-dimethyl substitution gives rise to moderate  values (0.17-0.42 for meso-phenyl-and 0.11-0.29 for meso-p-methylphenyl-substituted boron dipyrromethenes, depending on the solvent), the addition of two methyl groups at the positions 1-and 7-causes an increase in the fluorescence, with  up to the range 0.46-0.72. 34 Although substituents at the 8-position have normally the largest effect on the photophysical properties of BODIPY derivatives, modifications at the 3-and 2-positions also give rise to dyes with diverse properties.…”

“…34 While the 3,5-dimethyl substitution gives rise to moderate  values (0.17-0.42 for meso-phenyl-and 0.11-0.29 for meso-p-methylphenyl-substituted boron dipyrromethenes, depending on the solvent), the addition of two methyl groups at the positions 1-and 7-causes an increase in the fluorescence, with  up to the range 0.46-0.72. 34 Although substituents at the 8-position have normally the largest effect on the photophysical properties of BODIPY derivatives, modifications at the 3-and 2-positions also give rise to dyes with diverse properties. Extending the conjugation with double bonds at the 3-position yields fluorophores with a high brightness.…”