Sage Journals: Discover world-class research

Abstract

In order to investigate the changes in the spectroscopic properties of dimeric boron-dipyrromethenes (BODIPYs), four BODIPY derivatives are synthesized, including a monomer BODIPY in which a furyl group is substituted at the meso position and a dimer BODIPY with a furan group as a bridge. The four synthesized BODIPY derivatives are characterized through nuclear magnetic resonance and mass spectrometry. Photophysical properties such as ultraviolet–visible absorbance and the fluorescence emission of monomers (mT1 and mT2) and dimers (biT1 and biT2) are studied in eight different solvents. In addition, the relationship of their structural properties and optical properties are also considered through density functional theory calculations. The covalent link between the two BODIPY units using a furan group has a profound effect on the optical properties of the dimeric BODIPYs. We believe that an understanding of the synthesis and physical properties of dimeric BODIPYs will have a promising perspective in designing new BODIPY derivatives and predicting their spectroscopic characteristics in the future.

Keywords

BODIPY density functional theory dimer fluorescence furan

Introduction

Boron-dipyrromethene (BODIPY) derivatives were first reported by Kreuzer in the late 1960s as tricyclic complexes in which two dipyrrole units are connected by a methine bridge and centered on a boron atom.¹ BODIPY has attracted great interest from the scientific community for decades because of its high fluorescence quantum efficiency, narrow emission bandwidth, and excellent thermal and photochemical stability.^2–5 Several types of BODIPYs have been used as fluorescent probes for cell imaging and for the investigation of biological processes in vivo.^6–8 BODIPYs are widely used to label biologically essential molecules such as proteins, nucleotides and fatty acids, or to label intracellular organelles such as mitochondria and receptors.^9–14 Recently, BODIPYs have emerged as promising candidates in various fields such as electrochemical luminescence (ECL), organic solar cells, photodynamic therapy (PDT), logic gates, fluorescence thermometers, gas probes, and organic transistors.^15–22

Dimeric chromophores have often been found in Nature, such as in photosynthetic bacterial proteins and in natural light harvesting systems.²³ Such covalent pairs of chromophores in Nature have a long-standing interest in the scientific community. Since the BODIPY dimer was first reported by Akkaya, various kinds of derivatives have been synthesized and studied.^24–26 In particular, the photophysical properties of BODIPY can be fine-tuned for various applications through structural modification of the boron-dipyrine core and oligomerization including dimers. β–β-linked dimers, meso–meso-linked dimers and fused aromatic-linked dimers have been recently synthesized.^27–34 These BODIPY dimers show increased Stokes shifts and red-shifted luminescence. They can be used in organic solar cells or in biological applications, and have attracted significant attention as singlet oxygen photosensitizers, near infrared (NIR) fluorescence probes and electrochemiluminescence (ECL) sensors.^35–37 Although reports on covalently bonded BODIPY dimers are increasing, there is still a need to study the photophysical properties of heterocyclic bridged BODIPY dimers.^38–41

There have been previous reports of BODIPY dimers with furan bridges, such as 6⁴¹ and BDP-6.⁴⁰ Also, there are independent research results on the photophysical properties of the case where the methyl group (R³ position in Scheme 1) connected to the BODIPY moiety of BDP-6 causes steric hindrance with the hydrogen atom of furan, as well as the case of BODIPY dimer 6 in which steric hindrance does not occur. Based on this, we have tried to understand the systematic effect of steric hindrance on the photophysical properties of BODIPY dimers. In this study, we focus on meso-meso BODIPY dimers connected via a furan group, which is one of the heterocycles (Figure 1).^42–45 Initially, four types of BODIPY derivatives were designed to examine the photophysical properties of BODIPYs with a the furan group connection at the meso-position, and then the properties of the BODIPY dimer bridged by the furan group were examined. It was also considered that the methyl group (R³ position in Scheme 1) may interfere with intramolecular rotation due to steric hindrance with the hydrogen atom of the furan group. A systematic investigation into the properties of meso-meso-linked BODIPY dimers connected via a furan group can allow control of some of the basic parameters for the design principle and further advance the understanding of structure-property relationships.

Scheme 1.

Synthetic routes toward (a) mT1 and mT2, and (b) biT1 and biT2.

Figure 1.

Molecular structures of the furan-bridged BODIPY derivatives studied in this work.

Results and discussion

The synthesis of the furan-bridged BODIPY derivatives is depicted in Scheme 1. Furfural was condensed with pyrrole in the presence of a catalytic amount of trifluoroacetic acid to form dipyrranes 1 and 2, respectively. Because crude bis-dipyrranes 1 and 2 are unstable under column conditions, they were used directly in the next step without purification. Thus dipyrranes 1 and 2 were oxidized by an equivalent quantity of DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone), and the resulting dipyrrins were complexed using an excess amount of BF₃·Et₂O. Silica gel column chromatography purification subsequently provided BODIPYs mT1 and mT2 as solid powders in yields of 6% and 14%, respectively. In order to synthesize bis-BODIPYs biT1 and biT2, 2,5-furandicarboxaldehyde was used as the starting material. 2,5-Furandicarboxaldehyde was subjected to acid-catalyzed condensation with pyrrole to give the corresponding bis-dipyrranes 3 and 4. Similar to 1 and 2, crude bis-dipyrranes 3 and 4 are unstable under column conditions and were used directly in the next step without purification. Bis-dipyranes 3 and 4 were reacted with DDQ and then with BF₃·Et₂O in the presence of DIEA (N,N-diisopropylethylamine). Silica gel column chromatography purification using dichloromethane/hexane gave 5% of bis-BODIPY biT1 as a dark orange solid and 6% of bis-BODIPY biT2 as a dark red solid.

The BODIPY derivatives mT1, mT2, biT1 and biT2 were characterized by MALDI-MS, ¹H, and ¹³C NMR spectroscopy. In the MALDI-MS spectra of the BODIPY derivatives, molecular ion peaks confirmed the successful formation of the desired products (see the Supporting Information). The ¹H NMR spectra indicated that the protons attached to the sp³ hybridized carbons (C–H) and N–H protons present in dipyrranes 1 and 2 and bis-dipyrranes 3 and 4 had disappeared in BODIPY derivatives mT1, mT2, biT1, and biT2 (see the Supporting Information). The two β-furan protons of biT1 and biT2 occurred as singlets at 6.84 and 7.09 ppm, respectively. The furan protons of mT1 and mT2 appeared in the range of 6.44–7.71 ppm. The aromatic pyrrole protons present in mT2 and biT2 occurred as two separate signals between 6.27 and 7.22 ppm.

The ultraviolet (UV)–visible (UV-Vis) absorption and fluorescence spectra of BODIPY derivatives mT1, mT2, biT1, and biT2 were examined in eight different solvents. The absorption spectra of the four compounds are presented in Figure 2(a), and the photophysical properties are summarized in Table 1. The λ_abs values of the BODIPY derivatives depend slightly on the polarity of the solvent, and as the polarity of the solvent increased, the maximum absorption value shifted to the blue region. This trend is consistent with the phenomena occurring in several meso-aryl BODIPYs.^40–42 The BODIPY derivatives showed a strong absorption band at about 540 nm. The strong absorption at 540 nm is due to a strong S₀–S₁ electronic transition. In the cases of mT1, mT2, and biT1, a shoulder was observed around 400 nm, and biT2 showed a shoulder at 450 nm.

Figure 2.

Normalized (a) absorption and (b) emission spectra of the BODIPYs mT1, mT2, biT1, and biT2 in chloroform (λ_ex = 488 nm).

Table 1.

Photophysical properties of mT1, mT2, biT1, and biT2 in different solvents. The concentration used was 1.0 × 10^–5 M.

Compd	Solvent	λ_abs	λ_em	Stokes shift (nm)	Compd	Solvent	λ_abs	λ_em	Stokes shift (nm)
mT1	Hexane	544	573	29	biT1	Hexane	550	575	25
	Toluene	545	578	33		Toluene	545	589	44
	DCM	544	576	32		DCM	545	589	44
	Chloroform	545	576	31		Chloroform	545	590	45
	MeOH	538	571	33		MeOH	548	572	24
	Acetone	535	573	38		Acetone	545	584	39
	DMSO	544	576	32		DMSO	549	585	36
	MeCN	540	571	31		MeCN	545	586	41
mT2	Hexane	532	584	52	biT2	Hexane	546	631	85
	Toluene	536	588	52		Toluene	549	653	104
	DCM	532	589	57		DCM	546	675	129
	Chloroform	534	593	59		Chloroform	548	655	107
	MeOH	528	582	54		MeOH	540	667	127
	Acetone	528	584	56		Acetone	540	676	136
	DMSO	532	582	50		DMSO	542	584	42
	MeCN	526	581	55		MeCN	540	691	151

The wavelength of the main absorption band of mT1 was similar to that of biT1. In addition, the maximum absorption value changed slightly by changing the solvent polarity from hexane to acetonitrile (mT1: ~9 nm, biT1: ~5 nm), which reflects the typical tendency of BODIPY pigments. Compared to mT2, biT2 was observed to have a red-shifted shoulder band of about 50 nm, and the full width at half maxima of the major absorption band showed significantly larger values. This suggests that significant changes have occurred in the length and angle of the bond upon excitation.

A comparison of the emission spectra of the BODIPY derivatives is shown in Figure 2(b), and the solvatochromism data is summarized in Table 1. The emission maxima of biT1 and biT2 in chloroform were red shifted by 14 and 62 nm, respectively, compared to those of mT1 and mT2. However, biT1 and biT2 were observed to be more affected by the solvent polarity, and the emission maxima shifted to the red region in polar solvents. In polar media, the maximum red shift emission reflects a larger dipole in the charge-transfer (CT) excitation state, which is consistent with reports by Boens et al.⁴⁶ The Stokes shift value was the highest in biT2 among the four compounds. These results are similar to those of the previous work on BDP-6 and 6. When the methyl group (R³ position in Scheme 1) connected to the BODIPY causes steric hindrance with the hydrogen atom of the furan (biT1 and BDP-6), the molecule exists in a twisted form and the red-shift of the fluorescence wavelength is not large. In addition, when such steric hindrance does not occur (biT2 and 6), a large red-shift of the fluorescence wavelength is observed. This is because the less sterically hindered structure results in fully conjugated fluorescence emission. However, all four compounds had significantly lower quantum yields than the corresponding BODIPY monomers (see the Supporting Information). The low fluorescence intensity of the compounds may be associated with the electron-donating ability of the heteroatoms present in the bridging units. Furthermore, the much lower fluorescence intensities of biT1 and biT2 suggest that other non-radial decay processes (e.g. internal transformation or inter-system crossings from S₁ to T₁) might be more feasible in these compounds.

In order to gain detailed insights of the absorption bands, density functional theory (DFT) calculations were carried out using Gaussian 16 to optimize the geometries of the four derivatives and obtain molecular orbitals (MO).⁴⁷ All calculations were performed at the B3LYP/6-31⁺G* level without any solvation options. The resulting optimized geometries were double-checked with frequency calculation. Delocalization of the frontier molecular orbitals (FMO) of the four compounds represents important electronic bonds between the BODIPY unit and the furan group. Interestingly, the HOMO–LUMO band gap for biT1 (2.64 eV) is smaller than that of mT1 (2.77 eV); this trend is also reflected in the HOMO–LUMO band gap between biT2 (2.56 eV) and mT2 (2.81 eV). The HOMO–LUMO gaps generated by DFT do not directly corroborate with the experimentally observed (UV-Vis) energy clearance values, but reflect a similar trend of an increasing band gap (mT2 > mT1 > biT1 > biT2). In the case of biT2, destabilization of the LUMO is significantly lower because the approximately planar arrangement of the furan group increases the level of effective conjugation. However, in the case of biT1, it is difficult to arrange the plane due to the steric hindrance between the methyl group at the R³ position and the proton of furan, making it difficult to increase the effective conjugation level.

In the frontier molecular orbitals of the four molecules, the distribution of the HOMO and LUMO levels reflects the strong donor–acceptor interactions (Figure 3). In mT1 and mT2, the furan group has no electron density in the LUMO, while the HOMO state has a high electron density throughout the entire structure. The furan groups of biT1 and biT2 have a large electron density in the LUMOs, while the HOMO state has no electron density in the furan group. In the electronic absorption spectra of the four compounds, the main absorption band is associated with BODIPY absorption, which reflects that the origins of the main absorption peaks are the HOMO energy levels (Table 2). Overall, it can be seen that the DFT calculations were in good agreement with the experimental results.

Figure 3.

The frontier molecular orbitals of the BODIPYs mT1, mT2, biT1, and biT2 at the B3LYP/6-31⁺G* level for all the atoms.

Table 2.

Absorption data of compounds mT1, mT2, biT1, and biT2.

Compd	Experimental λ_abs (nm)	Calculated λ_abs (nm)
mT1	545	448
mT2	534	441
biT1	545	470
biT2	548	485

Conclusion

In conclusion, we have synthesized and characterized four BODIPY derivatives (mT1, mT2, biT1, and biT2) containing a furan group. Their absorbance and fluorescence, spectra were investigated and the structures were also examined by DFT studies. Derivatives mT1 and biT1 adopt non-planar conjugation due to the steric hindrance between the proton of the furan and the methyl substituent of the BODIPY moiety. Accordingly, it was observed that mT1 and biT1 did not show much difference in their UV absorbance and fluorescence emission. However, mT2 and biT2 do not have a methyl substituent on the BODIPY moiety, thereby enabling planar conjugation. This led to numerous differences in the UV absorbance and fluorescence emission between BODIPY monomer mT2 and dimer biT2. DFT calculations also showed the smallest HOMO-LUMO gap for biT2. Based on our understanding of the synthesis and physical properties of these BODIPY dimers, we plan to continue our studying the applications such compounds in, for example, photodynamic therapy and cell imaging.

Experimental

Materials

All the reagents and solvents used herein were purchased from commercial suppliers (Aldrich, Acros, and Merck) and used without further purification. Silica gel (60–120 mesh size) was used for flash column chromatography, and was purchased from Merck.

Equipment

High-resolution matrix-assisted laser desorption/ionization (MALDI) mass analysis was performed using an Autoflex III MALDI-TOF mass spectrometer (Bruker Daltonics, Germany) equipped with a smart beam laser as an ionization source. All the spectra were acquired with –19 kV accelerating voltage, a 100-Hz repetition rate, and in positive mode with an average of 500 shots. ¹H and ¹³C NMR spectra were acquired using a Bruker Avance 500-MHz spectrometer.

Synthesis

2,8-Diethyl-5,5-difluoro-10-(furan-2-yl)-1,3,7,9-tetramethyl-5H-dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide (mT1): Furfural (0.166 mL, 2 mmol) and 2,4-dimethyl-3-ethylpyrrole (0.54 mL, 4 mmol) were stirred in dry dichloromethane under a nitrogen atmosphere for 5 min, followed by the addition of a catalytic amount of trifluoroacetic acid. After confirming that the furfural has been consumed (TLC monitoring), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (454 mg, 2 mmol) was added slowly. After stirring at room temperature for 1 h, N,N-diisopropylethylamine (DIEA), (12.12 mL, 69.69 mmol) was added to the reaction mixture, followed by 30 min of additional stirring. Boron trifluoride diethyl etherate (BF₃·Et₂O), (12.12 mL, 95.748 mmol) was then added, and the reaction mixture was stirred for 16 h at room temperature. The solvent was evaporated under vacuum and the crude product was subjected to silica gel column chromatography with an eluting solvent of dichloromethane/hexane (80:20). mT1 was obtained as an orange-red powder in 6% yield (44.5 mg). ¹H NMR (500 MHz, CDCl₃): δ 7.63 (d, J = 4.5 Hz, 1H), 6.53 (dd, J = 5.5 Hz, J = 3 Hz, 1H), 6.44 (d, J = 6.5 Hz, 1H), 2.55 (s, 6H), 2.36 (m, 4H) 1.51 (s, 6H), 1.03 (m, 6H). ¹³C NMR (125.7 MHz, CDCl₃): δ 155.33, 146.13, 142.55, 138.51, 133.24, 132.53, 126.76, 118.76, 111.55, 17.25, 14.75, 12.78, 10.44. MALDI-MS: m/z [M+H]⁺ calcd for C₂₁H₂₆BF₂N₂O 371.2106; found: 371.068.

5,5-Difluoro-10-(furan-2-yl)-3,7-dimethyl-5H-dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide (mT2): Furfural (0.166 mL, 2 mmol) and 2-methylpyrrole (0.32 mg, 4 mmol) were stirred in dry dichloromethane under a nitrogen atmosphere for 5 min, followed by the addition of a catalytic amount of trifluoroacetic acid. After confirming that the furfural had been consumed (TLC monitoring), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (454 mg, 2 mmol) was added slowly. After stirring at room temperature for 1 h, N,N-Diisopropylethylamine (12.12 mL, 69.69 mmol) was added to the reaction mixture, followed by 30 min of additional stirring. Boron trifluoride diethyl etherate (12.12 mL, 95.748 mmol) was then added, and the reaction mixture was stirred for 16 h at room temperature. The solvent was evaporated under vacuum and the crude product was subjected to silica gel column chromatography with an eluting solvent of dichloromethane/hexane (50:50). mT2 was obtained as an orange-red powder in 14% yield (80.36 mg). ¹H NMR (500 MHz, CDCl₃) δ 7.71 (d, J = 4.5 Hz, 1H), 7.22(d, J = 7 Hz, 2H), 6.95 (d, J = 6.5 Hz, 1H), 6.62 (dd, J = 5.5 Hz, J = 3.0 Hz, 1H), 6.29 (d, J = 7 Hz, 2H) 2.62 (s, 6H). ¹³C NMR (125.7 MHz, CDCl₃) δ 157.09, 148.62, 146.07, 132.32, 129.76, 128.90, 119.38, 117.69, 112.56, 14.94. MALDI-MS: m/z [M+H]⁺ calcd for C₁₅H₁₄BF₂N₂O 287.1167; found: 287.025.

10,10'-(Furan-2,5-diyl)bis(2,8-diethyl-5,5-difluoro-1,3,7,9-tetramethyl-5H-dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide) (biT1): 2,5-Furandicarboxaldehyde (0.19 mg, 2 mmol) and 2,4-dimethyl-3-ethylpyrrole (4.32 mg, 8 mmol) were stirred in dry dichloromethane under a nitrogen atmosphere for 5 min, followed by the addition of a catalytic amount of trifluoroacetic acid. After confirming that the aldehyde had been consumed (TLC monitoring), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (908 mg, 4 mmol) was added slowly. After stirring at room temperature for 1 h, N,N-Diisopropylethylamine (24.24 mL, 139.38 mmol) was added to the reaction mixture, followed by 30 min of additional stirring. Boron trifluoride diethyl etherate (24.24 mL, 191.496 mmol) was then added, and the reaction mixture was stirred for 16 h at room temperature. The solvent was evaporated under vacuum and the crude product was subjected to silica gel column chromatography with an eluting solvent of EtOAc/hexane (15:85). biT1 was obtained as a red powder in 5% yield (67.3 mg). ¹H NMR (500 MHz, CDCl₃) δ 6.84 (s, 2H), 2.56 (s, 12H), 2.37 (m, 8H) 1.84 (s, 12H), 1.05 (t, J = 7.5 Hz, 12H). ¹³C NMR (125.7 MHz, CDCl₃) δ 155.23, 147.39, 137.72, 133.77, 131.27, 126.01, 115.76, 17.23, 14.43, 12.88, 12.69. MALDI-MS: m/z [M+H]⁺ calcd for C₃₈H₄₇B₂F₄N₄O 673.3872; found: 673.722.

10,10'-(Furan-2,5-diyl)bis(5,5-difluoro-3,7-dimethyl-5H-dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide) (biT2): 2,5-Furandicarboxaldehyde (0.19 mg, 2 mmol) and 2-methylpyrrole (0.64 mg, 8 mmol) were stirred in dry dichloromethane under nitrogen atmosphere for 5 min, followed by addition of catalytic amount of trifluoroacetic acid. After confirming that the aldehyde had been consumed (TLC monitoring), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (908 mg, 4 mmol) was added slowly. After stirring at room temperature for 1 h, N,N-Diisopropylethylamine (24.24 mL, 139.38 mmol) was added to the reaction mixture, followed by 30 min of additional stirring. Boron trifluoride diethyl etherate (24.24 mL, 191.496 mmol) was then added, and the reaction mixture was stirred for 16 h at room temperature. The solvent was evaporated under vacuum and the crude product was subjected to silica gel column chromatography with an eluting solvent of dichloromethane/hexane (80:20). biT2 was obtained as a red powder in 5% yield (60.6 mg). ¹H NMR (500 MHz, CDCl₃) δ 7.16 (d, J = 4 Hz, 4H), 7.09 (s, 2H), 6.27 (d, J = 4 Hz, 4H), 2.59 (s, 12H). ¹³C NMR (125.7 MHz, CDCl₃) δ 158.22, 151.45, 132.35, 129.76, 127.07, 120.14, 119.04, 15.06. MALDI-MS: m/z [M+H]⁺ calcd for C₂₆H₂₃B₂F₄N₄O 505.1994; found: 505.656. See the Supplemental Material for the NMR, Maldi MS, UV/Vis absorption and Fluorescence emission spectrum of mT1, mT2, biT1 and biT2.

Supplemental Material

sj-docx-1-chl-10.1177_17475198221143738 – Supplemental material for Photophysical properties of furan-bridged dimeric boron-dipyrromethene derivatives (BODIPYs)

Supplemental material, sj-docx-1-chl-10.1177_17475198221143738 for Photophysical properties of furan-bridged dimeric boron-dipyrromethene derivatives (BODIPYs) by Galam Jung, Namdoo Kim and Se Won Bae in Journal of Chemical Research

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Basic Science Research Program to Research Institute for Basic Sciences (RIBS) of Jeju National University through the National Research Foundation of Korea (NRF) funded by the Ministry of Education to S.W.B. (No. 2019R1A6A1A10072987) and by a research grant of Kongju National University in 2020 to N.K.

ORCID iD

Se Won Bae

Supplemental material

Supplemental material (BODIPYS SI.docx) for this article (CHL-22-0147) is available online.

References

Treibs

Kreuzer

FH.

Justus Liebigs Ann Chem 1968; 718: 208–223.

Boens

Leen

Dehaen

Chem Soc Rev 2012; 41: 1130–1172.

Liu

Zhou

, et al. Chem Comm 2015; 51: 1713–1716.

Kim

Bouffard

Kim

Chem A Eur J 2015; 21: 17459–17465.

Ulrich

Ziessel

Harriman

Angew Chem Int Ed 2008; 47: 1184–1201.

Gong

Guo

, et al. J Org Chem 2021; 86: 17110–17118.

Hou

Zhou

, et al. Anal Chem 2021; 93: 9640–9646.

Murale

Haque

Hong

, et al. Bull Korean Chem Soc 2021; 42: 111–114.

Miki

Kubo

, et al. Chem Comm 2021; 57: 1818–1821.

10.

Raskolupova

Popova

Zakharova

, et al. Molecules 2021; 26: 2679.

11.

Efimov

Fedunin

Chakhmakhcheva

Russ J Bioorg Chem 2011; 37: 249–253.

12.

Ren

Deng

Kong

, et al. Chem Comm 2016; 52: 6415–6418.

13.

Yang

Yin

, et al. Soft Matter 2016; 12: 8581–8587.

14.

Zhao

Zhang

, et al. J Am Chem Soc 2015; 137: 8490–8498.

15.

Arcudi

Ðorđević

Rebeccani

, et al. Adv Sci 2021; 8: 2100125.

16.

Squeo

Ganzer

Virgili

, et al. Molecules 2020; 26: 153.

17.

Bura

Leclerc

Fall

, et al. J Am Chem Soc 2012; 134: 17404–17407.

18.

Erbas-Cakmak

Cakmak

Topel

, et al. Chem Comm 2015; 51: 12258–12261.

19.

Zhang

Ahmed

Cong

, et al. Dyes Pigm 2021; 185: 108937.

20.

Liu

Yang

, et al. Dyes Pigm 2022; 199: 110053.

21.

Ozdemir

Choi

Kwon

, et al. ACS Appl Mater Interfaces 2016; 8: 14077–14087.

22.

Madhu

Kalaiyarasi

Basu

, et al. J Mater Chem C 2014; 2: 2534–2544.

23.

Alfieri

Panzella

Crescenzi

, et al. Eur J Org Chem 2021; 2021: 2982–2989.

24.

Coskun

Akkaya

EU.

J Am Chem Soc 2005; 127: 10464–10465.

25.

Shamova

Zatsikha

Nemykin

VN.

Dalton Trans 2021; 50: 1569–1593.

26.

Chung

Stafford

, et al. Polym Chem 2021; 12: 327–348.

27.

Ziessel

Harriman

Chem Comm 2011; 47: 611–631.

28.

Hayashi

Yamaguchi

Cha

, et al. Org Lett 2011; 13: 2992–2995.

29.

Pang

Zhang

Zhou

, et al. Chem Comm 2012; 48: 5437–5439.

30.

Bruhn

Pescitelli

Witterauf

, et al. Eur J Org Chem 2016; 2016: 4236–4243.

31.

Palao

Duran-Sampedro

de la Moya

, et al. J Org Chem 2016; 81: 3700–3710.

32.

Bruhn

Pescitelli

Jurinovich

, et al. Angew Chem Int Ed 2014; 53: 14592–14595.

33.

Nepomnyashchii

Bröring

Ahrens

, et al. J Am Chem Soc 2011; 133: 8633–8645.

34.

Ray

Bañuelos

Arbeloa

, et al. Dalton Trans 2016; 45: 11839–11848.

35.

Cakmak

Kolemen

Duman

, et al. Angew Chem Int Ed 2011; 50: 11937–11941.

36.

Poirel

De Nicola

Retailleau

, et al. J Org Chem 2012; 77: 7512–7525.

37.

Teesdale

Pupillo

, et al. J Am Chem Soc 2013; 135: 13558–13566.

38.

Huaulmé

Fall

Lévêque

, et al. Chem A Eur J 2019; 25: 6613–6620.

39.

Whited

Patel

Roberts

, et al. Chem Comm 2012; 48: 284–286.

40.

Wang

Zhang

, et al. Tetrahedron 2017; 73: 6894–6900.

41.

Kesavan

Das

Lone

, et al. Dalton Trans 2015; 44: 17209–17221.

42.

Kim

Easwaramoorthi

, et al. Inorg Chem 2010; 49: 4881–4894.

43.

Khan

Jana

Rao

, et al. Inorg Chim Acta 2012; 383: 257–266.

44.

Kesavan

Gupta

Dalton Trans 2014; 43: 12405–12413.

45.

Lager

Liu

Aguilar-Aguilar

, et al. J Org Chem 2009; 74: 2053–2058.

46.

Qin

Baruah

Van der Auweraer

, et al. J Phys Chem A 2005; 109: 7371–7384.

47.

Frisch

Trucks

Schlegel

, et al. Gaussian 16. Wallingford, CT: Gaussian, Inc., 2016.

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

1.39 MB