Cationic and Betaine-Type Boronated Acridinium Dyes: Synthesis

This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.

Article Cite This: ACS Omega 2019, 4, 2482−2492

http://pubs.acs.org/journal/acsodf

Cationic and Betaine-Type Boronated Acridinium Dyes: Synthesis, Characterization, and Photocatalytic Activity Krzysztof Durka, Mateusz Urban, Marek Dąbrowski, Piotr Jankowski, Tomasz Kliś, and Sergiusz Lulinś ki* Faculty of Chemistry, Department of Physical Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland

ACS Omega 2019.4:2482-2492. Downloaded from pubs.acs.org by 91.243.190.88 on 02/02/19. For personal use only.

S Supporting Information *

ABSTRACT: A series of isomeric boronated acridinium dyes were obtained by reactions of 10-(4′-octyloxyphenyl) functionalized 9(10H)-acridanone derivative with lithiated phenylboronic azaesters followed by aromatization with perchloric acid. The effect of the position of boronic group attached at ortho, meta, and para positions of the 9-phenyl ring on the photophysical properties was investigated. Conversion to related betaine trifluoroborato-substituted compounds was successfully performed, and the effect of this structural change on UV−vis absorption and fluorescence spectroscopy characteristics was established. Furthermore, cyclic voltammetry studies revealed that electrochemical behavior of cationic versus betaine structures is different in terms of redox potential values as well as stability. The theoretical calculations revealed a different scheme for molecular excitation processes in B(OH)2 versus BF3−-substituted compounds as charge transfer to acridinium core is observed from N-aryl or B-aryl moiety, respectively. Obtained compounds were active as photocatalysts in selected visible-light-promoted addition reactions to unsaturated substrates.

■

anionic boron-based groups, B(OH)2 and BF3−, respectively. Our study was aimed at evaluation of the effect of boron substituent variation on the photophysical properties. Specifically, we have raised a specific issue of charge distribution or, more precisely, separation of the positive charge of the organic cation from the negative charge of an anionic entity. In addition, photocatalytic activity of obtained compounds in selected reactions was tested.

INTRODUCTION Recently, a continuous interest in various types of acridine dyes is observed because of their interesting photophysical properties and biological activity. Various synthetic approaches to these compounds were developed, and many natural products possessing the acridine scaffold were isolated.1,2 Basic research concerning acridinium dyes was mostly aimed at characterization of charge-transfer processes in those compounds during electron excitation.3−11 From the practical point of view, significant efforts have been devoted to utilizing acridine dyes as sensor materials for detection of anions12−15 as well as for biolabeling purposes.16−18 There is also an increased interest in their use as components for the construction of organic light-emitting diodes (LEDs)19−22 and solar cells.23 Furthermore, selected derivatives exhibit potent chemiluminescence, making them useful in clinical diagnostics.24−26 Among various compounds comprising acridine scaffold, cationic acridinium dyes feature the reactive 9-position which has been exploited in designing dynamic supramolecular systems27,28 as well as for pseudobase formation.29,30 Recently, photocatalytic properties of selected acridinium dyes with a special emphasis on 9-mesitylacridinium derivatives were discovered. Since then, numerous reports on the use of these compounds in visible-light induced organic transformations were published, especially by the groups of Fukuzumi and Nicewicz.31−49 In this contribution, we describe two series of regioisomeric acridinium dyes bearing the neutral or the © 2019 American Chemical Society

■

RESULTS AND DISCUSSION Synthesis. Following the reported procedures,19,41 in the first step, 9(10H)-acridanone was subjected to Cu(I)-catalyzed N-arylation with 1-iodo-4-octyloxybenzene50 to give compound 4 in high yield (Scheme 1). The n-octyloxy chain was introduced to improve the solubility of the intermediate ketone 4 as well as final acridinium products 5−10. Reactions of 2(halophenyl)-6-butyl[1,3,6,2]dioxazaborocans 1−351 with nBuLi were performed by addition of a tetrahydrofuran (THF) solution of 1−3 to a precooled (−80 °C, internal temperature) solution of n-BuLi in THF (ca. 0.6 M). The mixture needed to be stirred for 30 min at ca. −75 °C to complete the interconversion. The resultant lithiated arylboronate intermediates are sufficiently stable under these conditions; Received: November 26, 2018 Accepted: January 18, 2019 Published: February 1, 2019 2482

DOI: 10.1021/acsomega.8b03290 ACS Omega 2019, 4, 2482−2492

ACS Omega

Article

Scheme 1. Synthesis of N-Arylated Acridanone Derivative 4

Scheme 3. Synthesis of Betaine-Type TrifluoroboratoSubstituted Acridinium Derivatives 8−10

however, slow decomposition was observed to some extent above −70 °C, resulting in lower product yields. Subsequent addition of a solution of 4 in THF followed by hydrolysis gave respective carbinols which were converted to targeted acridinium salts 5−7 by addition of 70 wt % HClO4 (Scheme 2). The products were isolated in good yields as bright yellow (5 and 7) or pale-orange (6) powders well soluble in polar organic solvents and insoluble in water. The synthesis of zwitterionic trifluoroborato derivatives was accomplished by mixing compounds 5−7 in acetone with excess of aqueous KHF2 followed by evaporation of a resulting mixture and extraction of a product 8−10 with acetone (Scheme 3). Compounds 5−10 were fully characterized by multinuclear (1H, 13C, 11B, 19F) NMR spectroscopy. The presence of B(OH)2 group in 5−7 was directly confirmed by the 11B NMR spectra showing broad resonances at ca. 28 ppm. In the case of 8−10, broad 11B NMR signals were found in the range of 3−9 ppm, whereas 19F NMR spectra showed resonances at ca. −140 ppm in agreement with values reported for various organotrifluoroborates.52 In addition, the structure of 9 was confirmed by X-ray diffraction (Figure 1a). The molecular conformation resembles that found for related acridinium derivatives showing that both benzene rings are oriented almost perpendicularly with respect to the acridinium core. The dihedral angles between acridinium moiety and phenyl rings bearing octyloxy and trifluoroborato functionalities are equal to 87.80(1) and 78.00(1), respectively. The supramolecular organization is mostly defined by the electrostatic interactions between BF3− and central positively charged acridinium ring. Each trifluoroborato moiety is sandwiched between two such rings (Figure 1c). Because of the perpendicular alignment of aromatic rings, the structure expands into a three-dimensional network (Figure 1b). Thermogravimetric analysis (TGA) revealed that compounds 5−10 are quite stable up to 250−300 °C (for details, see the Supporting Information, Figures S37−S42). A small yet detectable mass loss of ca. 2−3% was observed for 5−8 at lower temperatures (ca. 120−160 °C) corresponding to melting points of these compounds [confirmed by endothermic peaks in the respective differential scanning calorimetry (DSC) curves]. This can be due to the escape of residual

solvents including water released during dehydration of boronic groups in 5−7. At higher temperatures (above 250 °C), exothermic degradation processes occur. They are accompanied by the mass loss of ca. 25−30% for perchlorate salts 5−7 and 35−70% for betaine-type dyes 8−10. Electrochemical Properties. The electrochemical properties of 5−10 were studied using cyclic voltammetry (CV) measurements in dichloromethane (DCM) with respect to the Fc/Fc+ redox couple (Figure 2) and reported with respect to saturated calomel electrode (SCE) (Table 1) for a direct comparison with data reported for analogous acridinium derivatives.43 For irreversible redox processes, the oxidation and reduction half-potentials (Eox1/2, Ered1/2) were estimated based on the onset values. In the remaining cases, they were calculated as the mean value of anodic and cathodic peak potentials. Compound 5 displays reversible oxidation at 1.15 V. Unlike 5, its regioisomers 6 and 7 show quasireversible oxidation processes which indicates that oxidation is followed by chemical reactions. For betaine-type compounds 8−10, the oxidation is fully irreversible which is in line with the increased reactivity of the C−BF3− bond because of its relatively stronger nucleophilic character with respect to compounds bearing B(OH)2 functionality. The reduction potentials for 5−7 span in a rather narrow range from −0.58 to −0.67 V and are slightly lower than those found for commonly used 9mesitylacridinium photocatalysts.43 Neutral (zwitterionic) compounds 8−10 have their ground-state reduction potentials negatively shifted in comparison to 5−7. The most negative value of Ered1/2 = −0.97 eV was observed for the ortho-BF3− derivative 10 and it is even lower than that reported recently for a compound bearing strongly electron-donating methoxy groups attached to the acridinium core (Ered1/2 = −0.84 eV).43 On the basis of the oxidation and reduction potentials, molecular orbital levels were established and energy gap values were estimated (Table 1). For betaine-type compounds 8−10, they are higher than those obtained for their respective cationic precursors. It should be noted that the biggest difference of 0.57 eV is between band gaps for ortho-substituted derivatives 7 (2.18 eV) and 10 (2.75 eV), which indicates that the

Scheme 2. Synthesis of Boronic Group-Substituted Acridinium Derivatives 5−7

2483


ACS Omega

Article

Figure 1. (a) Molecular (ellipsoids drawn on 50% probability level) and (b) supramolecular structure of 9. (c) Intermolecular contacts between BF3− group and acridinium core are additionally depicted.

Figure 2. Cyclic voltammograms of 5−10 (1 mM) in Bu4NPF6/CH2Cl2. Measurements were taken at a scan rate of 100 mV s−1.

absorption spectra of all compounds show three distinct bands at ca. 435, 360, and 345 nm in DCM, in agreement with data for analogous compounds.53 In addition, the longest wavelength absorption band at ca. 435 nm exhibits a characteristic fine structure featuring two side bands of a lower intensity. The molar absorption coefficients of 5−10 range from ε = 8780 to 12 700 M−1 cm−1, which is considerably higher than the value reported for the related 9mesityl-10-methylacridinium perchlorate (ε = 5600 M−1 cm−1).53 Structural changes and the kind of solvent do not strongly influence the positions of absorption bands for compounds 5−7. For betaine structures 8−10, the slight blue shift (up to 11 nm) was observed with increased solvent polarity (when DCM was replaced with acetonitrile). One can also clearly see that the position of BF3− is also important as the blue shift of 16 nm (in DCM) is observed when going from para to ortho isomer. Some distinct features can be noted when analyzing emission spectra of 5−10. In DCM a slight blue shift of 12 nm is observed when changing the location of the B(OH)2 group from para to ortho position. In turn, a stronger blue shift of 21 nm can be observed when moving of BF3− group from para to ortho position. This indicates that the emission

Table 1. Redox Potentials and Energy Band Gaps for 5−10 Based on CV Measurementsa 5 6 7 8 9 10

Ered1/2/V

Eox1/2/V

ELUMO/eV

EHOMO/eV

ΔE/eV

−0.59 −0.67 −0.58 −0.80 −0.70b −0.97

1.55 1.59 1.60 1.71b 1.69b 1.78b

−3.81 −3.73 −3.82 −3.60 −3.70 −3.43

−5.95 −5.99 −6.00 −6.11 −6.09 −6.18

2.14 2.26 2.18 2.51 2.39 2.75

a

All values are given with respect to SCE using the conversion E (vs SCE) = E (vs Fc/Fc+) + 0.400 V. bOnset value.

electronic properties of the acridinium system are influenced due to some specific interaction between acridinium ring and boron-based functional groups. Photophysical Properties of 5−10. The optical properties of 5−10 were investigated by UV−vis absorption in solution under ambient conditions. To study solvatochromic phenomena, measurements were performed in three solvents differing in polarityDCM, acetonitrile, and toluene (Figure 3, Table 2). Additional spectra and overlays are presented in the Supporting Information (Figures S19−S30). UV−vis 2484


ACS Omega

Article

Figure 3. Overlay of normalized UV−vis absorption and emission spectra in DCM for (a) 5−7 and (b) 8−10.

Table 2. Optical Properties of Compounds 5−10 experimental −1

compound

solvent

λmax/nm

5

DCM toluene MeCN DCM toluene MeCN DCM toluene MeCN DCM tolueneb MeCN DCM toluene MeCN DCM toluene MeCN

436 432 430 436 434 430 431 433 428 446

8780 10 400 8130 11 800 7790 10 300 10 700 10 400 9880 12 700

435 441 436 431 430 433 426

9660 10 800 8470 10 900 10 900 7630 10 200

6

7

8

9

10

ε/M

−1

cm

λem/nm

TD-DFT −1

Δ/cm

Φ/%

λabs/nm

λem/nm

544 518

4550 3840

1.9 2.2

416

524

540 526

4420 4030

1.7 1.2

435

482

532 524

4400 4010

1.0 0.3

414

481

536

3760

1.3

412

534

527 524

3700 3850

3.4 3.9

417

486

515 514

3840 3640

2.4 0.3

421

484

a

a

Samples in DCM were excited at the absorption maximum at the longest wavelength and all samples in toluene were excited at 433 nm; standard: coumarine 153 in EtOH, c = 4 × 10−6 M, RT, QY = 0.544).54 Δ denotes the Stokes shift. bSpectra of 8 were not measured due to lack of solubility in toluene.

properties of betaine structures 8−10 are more sensitive to the change of the position of the boron-based groups than one observes in their cationic counterparts 5−7. A significant solvatochromism was observed for 5 where the bathochromic shift of the emission band occurs in DCM solution (λem = 544 nm vs 518 nm in toluene). The analogous red shift was detected also for 6 and 7, but it was much weaker (14 and 8 nm, respectively). In contrast, data obtained for 9−10 (compound 8 was completely insoluble in toluene) indicate lack of solvatochromism for betaine-type structures. Overall, the emission spectra show one broad band and only in case of 9 and 10 the fine structure was observed. All analyzed compounds exhibited rather weak emission as the highest quantum yield (QY) of 0.034 was determined for 9. This is in agreement with literature data which indicate that introduction of 9-aryl group to the acridinium system results in strong quenching of fluorescence. Theoretical Calculations. Theoretical calculations performed at PBE0/6-311+G(d,p) level of theory revealed that the mechanism responsible for the electron transition is different for cationic and zwitterionic derivatives (Figure 4). To simplify the calculations, the long octyloxy chain was replaced with the ethoxy group in all studied structures.

Figure 4. Plot of the molecular orbitals mostly responsible for the electron excitation in 5 and 8. Blue and red areas correspond to negative and positive signs of the function, respectively, depicted with isovalue of 0.2 e Å−3.

According to expectations, in all systems, the lowest unoccupied molecular orbital (LUMO) orbital is located on the central acridinium core. In the case of compounds 5 and 7 three highest occupied molecular orbitals (HOMOs, almost degenerate) are confined on the ClO4− anion; however, the time-dependent density functional theory (TD-DFT) calculations show that corresponding electron transitions are not effective (Figure 5). Instead, values of ground-state oscillator strengths suggest that the excitation occurs from the HOMO − 2485


ACS Omega

Article

Figure 5. Diagram representing the energies of HOMO − 4 to LUMO molecular orbitals (eV) for 5−10 derived from DFT calculations. The locations of molecular orbitals are represented by the colors according to the given molecular schemes. The orbitals that do not take part in the excitation process are marked in gray.

3 and HOMO − 4 orbitals located on the electron rich alkoxysubstituted N-aryl ring (NPh). For compound 6, the hydrogenbond interaction between B(OH)2 and ClO4− entities stabilizes orbital levels located on the ClO4− anion, thus changing the order of HOMO levels. Besides, the excitation mechanism operating in this system remains unchanged, that is, the charge transfer occurs from the N-aryl moiety to the acridinium core. This goes in line with the calculated absorption maxima, which are in agreement with experimental values. A different scheme for electron excitation is observed for 8−10 where the HOMO spans across the BF3−-aryl moiety or is additionally spread on acridinium core. The energies of molecular orbitals located on the N-aryl moiety are lower and, according to TD-DFT calculations, they do not contribute to an excitation process. Consequently, in 8−10 the electric density flows from BF3−-substituted phenyl ring to the acridinium core, although the contribution of π−π* excitation on the acridinium ring is also important. The calculated values of absorption maxima are close to experimental ones (they are usually lower by about 20 nm). It is also noticeable that the LUMO level of 10 is elevated with respect to regioisomers 8 and 9. This is in agreement with the results obtained from CV measurements. Regarding the emission characteristics, the calculations underestimate the experimental wavelengths, except for parasubstituted derivatives 5 and 8. At this point, it should be noted that calculations were performed for an isolated molecule but the interaction with solvent molecules of such a species with strong charge separation may significantly affect the energy levels and excitation processes. Furthermore, the transition to triplet state can also be expected.55−57 The fluorescent QYs were also small, suggesting the nonradiative decay of excited states. Observed differences can be rationalized in terms of different molecular geometries and charge distribution. In contrast to 5−7, the acridinium and (trifluoroborato)phenyl moieties in

8−10 are not aligned in a perpendicular fashion as the angle between corresponding mean square planes are 52.7° (8), 54.0° (9) and 75.4° (10). This should facilitate the charge transfer between BF3−−aryl group and acridinium core. Furthermore, the alternation between the neutral boronic group (being a weak electron-acceptor) and the anionic trifluoroborato group (a strong electron-donor) results in differentiation of the charge distribution within the acridinium and the phenyl ring attached at C-9 (Figure 6, Table S3 in Supporting Information). In all studied systems, the N-aryl group is negatively charged (−0.1 to −0.3 e) and remains almost unaffected by the type and position of boron-based group. The positive charge of a central acridinium ring in 5−7 (1.2−1.4 e) is larger than that in 8−10 (+0.8 to 1.1 e), while BF3−−aryl group bear significant negative charge of about −0.7

Figure 6. Distribution of Mulliken charges in molecules 5 and 8. Numerical values for all compounds are provided in Tables S2 and S3 in the Supporting Information. The vector of dipole moment is additionally depicted (blue arrow). 2486


ACS Omega

Article

Table 3. Excited-State Reduction Potentialsa for Compounds 5−10

e. Furthermore, the C9 carbon atom of acridinium core becomes significantly less electrophilic in zwitterionic compounds 8−10 as indicated by its strongly reduced positive charge (+0.36 vs +1.20 e for 8 and 5, respectively). In turn, the neighbored carbon atom from BF3−−aryl ring is more electropositive (+1.38 e vs +0.78 e for 8 and 5, respectively). It is also important to note that magnitude and orientation of dipole moment are different for both classes of boronated acridines. In 5, it is equal to 11.8 D (μ = 12.1 D in 6, μ = 13.1 D in 7) and points perpendicularly to acridine moiety from the ClO4− anion. Naturally, the vector orientation would be strongly affected by the position of the ClO4− counterion; however, we suppose that in weakly coordinative solvents such as DCM or toluene, contact ion pairs resembling the optimized geometries are highly expected. This is in accordance with UV−vis spectroscopic studies showing that the position of absorption and emission bands are only slightly affected by solvent polarity. In turn, zwitterions 8−10 are highly polar (μ = 30.1 D for 8, μ = 25.7 D for 9, μ = 14.2 D for 10) with dipole moment vectors roughly pointing from (trifluoroborato)phenyl to N-aryl groups. Photocatalytic Activity. Preliminary results concerning photocatalytic activity of 5−10 were obtained. We have found that these compounds catalyze the visible light-mediated atom transfer radical addition (ATRA) of 1-iodoperfluorobutane to ethynyl MIDA-boronate (Scheme 4).58 The reaction afforded

5 6 7 8 9 10

E1/2(M+/M*)/V

E1/2(M*/M−)/V

E(0,0)b/eV

−1.02 −0.99 −1.02 −0.83 −0.88 −0.87

1.98 1.91 2.04 1.74 1.87 1.68

2.57 2.58 2.62 2.54 2.57 2.65

Calculated using the equations: E1/2(M+/M*) = Eox1/2 − E(0,0); E1/2(M*/M−) = Ered1/2 + E(0,0). bDetermined by calculating the energy of the wavelength of the intersection of the UV−vis absorption and emission bands. a

Scheme 5. Photocatalytic Addition of Methanol to Diethyl Ethylidenemalonate

bearing the B(OH)2 group at the ortho position. The control experiment in the absence of light did not afford 12, suggesting that a photoactivated catalyst is involved in the reaction; however, mechanism of the reaction is not clear and will be the subject of further studies in our group.

■

Scheme 4. Iodoperfluorobutylation of Ethynyl MIDABoronate Catalyzed by 5−10

CONCLUSIONS In conclusion, a series of three isomeric boronated acridinium perchlorate salts and their zwitterionic trifluoroborato counterparts have been prepared and comprehensively characterized. UV−vis absorption and fluorescence maxima of these compounds depend markedly on both the position and the kind of boron substituent. In general, the red shift is observed when moving the boron substituent from ortho to para position of the boronated phenyl ring. Also, the electrochemical behavior is attenuated by the total charge of the entire acridinium system, as CV measurements revealed that the ground state potentials E1/2(M+/M) and E1/2(M/M−) are significantly lower for zwitterionic derivatives 8−10. Furthermore, TD-DFT calculations revealed a strong impact of the structure and position of the boron-based group on the photophysical characteristics of studied systems which is especially manifested by varying nature of electron excitation processes. From the practical point of view, it is important that obtained compounds proved to be effective organic photocatalysts in selected addition reactions to substrates bearing double and triple carbon−carbon bonds. Further work will be undertaken to disclose new visible light photocatalytic protocols whose specificity will rely on the use of obtained boronated acridinium dyes.

functionalized vinyl MIDA-boronate 11 as the mixture of two different isomers (E/Z = 0.35/1) in 45% yield for 5−9 and 55% for 10. The catalytic cycle involves oxidation of sodium ascorbate by the excited catalyst followed by reduction of C4F9I. As the compounds 5−10 are rather moderate reductants, their ability to reduce C4F9I (Ered1/2 < −1.0 V vs SCE)59 is surprising based on the electron transfer mechanism. However, the incompatibility of the redox potentials has been observed earlier in some reactions catalyzed by [Acr+Mes]ClO4 (Ered1/2 = −0.5 V vs SCE).44 For example, in the aerobic oxidation of benzyl alcohols60 the key step involves the reaction of benzylic radical with superoxide O2•− generated upon reduction of the molecular oxygen (Ered1/2 = −0.87 V vs SCE).61 Next, we tried to check the oxidation potential of our acridinium dyes. We decided to use the protocol developed by Koike and Akita,62 where the alkyl radicals generated via oxidation of alkyltrifluoroborates by the excited [Acr+-Mes]ClO4 reacted with electron deficient alkenes. However, for 5− 7 and 10, the reaction of potassium cyclobutyltrifluoroborate with diethyl ethylidenemalonate did not proceed at all which can be ascribed to lower excited-state reduction potentials E1/2(M*/M−) for 5−10 (they range from 1.68 to 2.04 V, see Table 3) with respect to [Acr+-Mes]ClO4 (2.08 V).43 However, the reaction afforded compound 12 because of the formal addition of methanol to the double bond (Scheme 5). The best conversion (76%) was observed for compound 7

■

EXPERIMENTAL SECTION General Comments. All reactions involving air- and moisture-sensitive reagents were carried out under an argon atmosphere. Solvents were stored over sodium wire before use. Key reagents including arylboronic acids, BDEA, and nbutyllithium (10 M solution in hexanes) were purchased from Aldrich and used as received. The NMR chemical shifts are given relative to tetramethylsilane using known chemical shifts of residual proton (1H) or carbon (13C) solvent resonances. 11 B and 19F NMR chemical shifts are given relative to BF3·Et2O 2487


ACS Omega

Article

and CFCl3, respectively. In the 13C NMR spectra, the resonances of carbon atoms bound to boron were not observed because of their broadening by quadrupolar boron nucleus. 2-(4′-Bromophenyl)-6-butyl[1,3,6,2]dioxazaborocan (1). A mixture of 4-bromophenylboronic acid (20.1 g, 0.1 mol), N-butyldiethanolamine (17.0 g, 0.105 mol), and toluene (100 mL) was heated with stirring for 1 h at ca. 60 °C. Water was separated and the organic phase was concentrated under reduced pressure to remove the majority of toluene. To a remaining viscous solution, hexane (100 mL) was added to precipitate a crystalline material. It was filtered, washed with diethyl ether (2 × 25 mL) and dried under vacuum (10−3 Torr) at 60 °C for 10 h to give the title compound, mp 126− 127 °C. Yield: 31.0 g (95%). 1H NMR (CDCl3, 400 MHz): δ 7.43 (d, J = 8.0 Hz, 2H), 7.34 (d, J = 8.0 Hz, 2H), 4.10−4.00 (m, 4H), 3.00−2.90 (m, 4H), 2.21−2.17 (m, 2H), 1.45−1.37 (m, 2H), 1.10−1.00 (m, 2H), 0.76 (t, J = 7.0 Hz, 3H) ppm. 13 C NMR (CDCl3, 100.6 MHz): δ 135.0, 130.1, 121.8, 62.9, 59.7, 57.2, 30.8, 26.7, 19.9, 13.6 ppm. 11B NMR (CDCl3, 64.16 MHz): δ 7.3 ppm. Anal. Calcd for C14H21BBrNO2: C, 51.56; H, 6.49; N, 4.29. Found: C, 51.39; H, 6.57; N, 4.23. Compounds 2 and 351 have been prepared analogously starting with 3- and 2-bromophenylboronic acid, respectively. 2-(3′-Bromophenyl)-6-butyl[1,3,6,2]dioxazaborocan (2). Yield: 30.3 g (93%), mp 120−122 °C. 1H NMR (CDCl3, 400 MHz): δ 7.73 (d, J = 1.0 Hz, 1H), 7.51 (d, J = 7.5 Hz, 1H), 7.36 (ddd, J = 7.5, 2.0, 1.0 Hz, 1H), 7.14 (t, J = 7.5 Hz, 1H), 4.20−4.08 (m, 4H), 3.06−2.95 (m, 4H), 2.30−2.26 (m, 2H), 1.52−1.44 (m, 2H), 1.17−1.07 (m, 2H), 0.81 (t, J = 7.0 Hz, 3H) ppm. 13C NMR (CDCl3, 100.6 MHz): δ 136.0, 131.7, 130.4, 129.1, 122.4, 63.0, 59.8, 57.4, 26.9, 20.1, 13.7 ppm. 11B NMR (CDCl3, 64.16 MHz): δ 7.5 ppm. Anal. Calcd for C14H21BBrNO2: C, 51.56; H, 6.49; N, 4.29. Found: C, 51.86; H, 6.54; N, 4.15. 2-(2′-Bromophenyl)-6-butyl[1,3,6,2]dioxazaborocan (3). Yield: 31.0 g (95%), mp 91−93 °C. 1H NMR (CDCl3, 400 MHz): δ 7.77 (dd, J = 8.0, 1.5 Hz, 1H), 7.47 (dd, J = 8.0, 1.0 Hz, 1H), 7.20 (td, J = 8.0, 1.0 Hz, 1H), 7.06 (td, J = 8.0, 1.5 Hz, 1H), 4.18−4.06 (m, 4H), 3.30−3.23 (m, 2H), 3.04−2.99 (m, 2H), 2.62−2.58 (m, 2H), 1.55−1.47 (m, 2H), 1.19−1.10 (m, 2H), 0.81 (t, J = 7.0 Hz, 3H) ppm. 13C NMR (CDCl3, 100.6 MHz): δ 136.8, 133.2, 129.4, 129.2, 126.2, 62.9, 58.17, 58.11, 26.8, 20.1, 13.6 ppm. 11B NMR (CDCl3, 64.16 MHz): δ 8.5 ppm. Anal. Calcd for C14H21BBrNO2: C, 51.56; H, 6.49; N, 4.29. Found: C, 51.52; H, 6.44; N, 4.22. 9(10H)-10-(4′-Octyloxyphenyl)acridanone (4). 9(10H)Acridanone (4.88 g, 25 mmol, 1.0 equiv), 1-iodo-4octyloxybenzene (9.96 g, 30 mmol, 1.2 equiv), K2CO3 (4.55 g, 33 mmol, 1.32 equiv), CuI (0.58 g, 3.1 mmol, 12 mol %), and 2,2,6,6-tetramethyl-3,5-heptanedione (1.10 g, 6.0 mmol, 24 mol %) were suspended in dry dimethylformamide (60 mL). The reaction mixture was heated at 180 °C for 3 days, and the resulting precipitate was filtered. The crude product was washed with 3 M HCl, water, and MeOH to afford the title compound as a pale yellow solid, mp 139−141 °C. Yield 8.4 g, (84%). 1H NMR (400 MHz, CDCl3): δ 8.56 (dd, J = 8.1, 1.6 Hz, 2H), 7.48 (ddd, J = 8.6, 6.9, 1.7 Hz, 2H), 7.29− 7.19 (m, 4H), 7.15 (d, J = 8.9 Hz, 2H), 6.82 (d, J = 8.3 Hz, 2H), 4.07 (t, J = 6.5 Hz, 2H), 1.99−1.68 (m, 2H), 1.62−1.19 (m, 10H), 0.93−0.88 (m, 3H) ppm. 13C NMR (101 MHz, CDCl3): δ 178.14, 159.75, 143.51, 133.19, 131.05, 130.90, 127.20, 121.82, 121.41, 116.94, 116.59, 68.49, 31.84, 29.38,

29.27, 29.25, 26.10, 22.69, 14.14 ppm. Anal. Calcd for C27H29NO2 (399.5247): C, 81.17; H, 7.32; N, 3.51. Found: C, 81.25; H, 7.38; N, 3.26. 9-[4′-(Dihydroxyboryl)phenyl)]-10-(4″-octyloxyphenyl)acridinium Perchlorate (5). A solution of 2 (3.26 g, 10 mmol) in THF (20 mL) was added dropwise to a precooled (−80 °C) solution of n-BuLi (1.6 M, 6.2 mL, 10 mmol) in THF (20 mL). The resulting solution was stirred for 30 min followed by the addition of a solution of 1 (2.0 g, 5.0 mmol) in THF (20 mL). The temperature was maintained below −75 °C during the reactions. The resulting mixture was stirred for 30 min and hydrolyzed with water. Then, concd HClO4 (1 mL) was added dropwise which resulted in an intense yellow coloration of the mixture. The organic phase was separated while the water phase was extracted with DCM (2 × 20 mL) evaporation of organic solution afforded yellow viscous residue which was washed with water and redissolved in DCM (50 mL). The solution was filtered and concentrated and the product was precipitated with Et2O (50 mL). The obtained yellow suspension was stirred for 2 h and filtered. The product was washed with Et2O (2 × 20 mL) and dried to give 5 as a yellow powder, mp (glass) 115−120 °C. Yield 2.1 g (83%). 1H NMR (400 MHz, acetone-d6): δ 8.38−8.30 (m, 2H), 8.28 (d, J = 8.1 Hz, 2H), 8.15 (d, J = 8.7 Hz, 2H), 8.02−7.92 (m, 2H), 7.82− 7.76 (m, 4H), 7.68 (d, J = 8.0 Hz, 2H), 7.50 (d, J = 8.8 Hz, 2H), 4.29 (t, J = 6.5 Hz, 2H), 2.03−1.83 (m, 2H), 1.73−1.55 (m, 2H), 1.56−1.28 (m, 8H), 0.94 (d, J = 6.7 Hz, 3H) ppm. 13 C NMR (101 MHz, acetone-d6): δ 162.95, 161.40, 142.96, 138.55, 135.14, 134.51, 129.78, 129.30, 129.14, 128.05, 126.11, 119.98, 116.83, 68.62, 31.71, 29.22, 29.16, 29.05, 25.94, 22.46, 13.52 ppm. 11B NMR (96 MHz, acetone-d6): δ 28.5 ppm. HRMS (ESI) m/z: calcd for C33H35BNO3+ ([M]+), 504.2705; found, 504.2704. 9-[3′-(Dihydroxyboryl)phenyl)]-10-(4″-octyloxyphenyl)acridinium Perchlorate (6). This compound was obtained as described for 5 using 2 as a starting material. Pale orange powder, mp (glass) 120−125 °C. Yield 2.0 g (79%). 1H NMR (300 MHz, acetone-d6): δ 8.38−8.26 (m, 3H), 8.18−8.09 (m, 3H), 7.96 (ddd, J = 8.7, 6.8, 0.9 Hz, 2H), 7.87−7.75 (m, 4H), 7.52 (d, J = 9.1 Hz, 2H), 4.28 (t, J = 6.5 Hz, 2H), 2.02−1.85 (m, 2H), 1.68−1.54 (m, 2H), 1.55−1.27 (m, 8H), 0.93 (t, J = 6.2 Hz, 3H) ppm. 13C NMR (101 MHz, acetone-d6): δ 163.35, 161.38, 142.96, 138.50, 135.96, 135.50, 131.73, 129.84, 129.35, 129.30, 128.16, 127.99, 126.25, 119.95, 116.86, 116.83, 68.63, 31.73, 29.23, 29.17, 29.07, 25.95, 22.47, 13.55 ppm. 11B NMR (96 MHz, acetone-d6): δ 27.3 ppm. HRMS (ESI) m/z: calcd for C33H35BNO3+ ([M]+), 504.2705; found, 504.2701. 9-[2′-(Dihydroxyboryl)phenyl)]-10-(4″-octyloxyphenyl)acridinium Perchlorate (7). This compound was obtained as described for 5 using 3 as a starting material. Yellow powder, mp (dec) 156−158 °C. Yield 2.2 g (87%). 1H NMR (400 MHz, acetone-d6): δ 8.33−8.25 (m, 4H), 8.06−8.00 (m, 2H), 7.91 (dd, J = 6.8, 0.9 Hz, 1H), 7.89 (dd, J = 6.8, 0.9 Hz, 1H), 7.85−7.78 (m, 3H), 7.78−7.73 (m, 2H), 7.67−7.64 (m, 1H), 7.52−7.49 (m, 2H), 6.93 (br, 2H), 4.28 (t, J = 6.5 Hz, 2H), 2.01−1.82 (m, 2H), 1.65−1.54 (m, 2H), 1.51−1.29 (m, 8H), 0.92 (t, J = 6.1 Hz, 3H) ppm. 13C NMR (101 MHz, acetoned6): δ 167.64, 161.38, 142.34, 138.44, 135.51, 130.25, 130.02, 129.61, 129.37, 129.29, 127.62, 126.65, 119.61, 116.96, 116.83, 68.62, 31.71, 29.21, 29.05, 25.93, 22.45, 13.50 ppm. 11B NMR (96 MHz, acetone-d6): δ 27.8 ppm. HRMS (ESI) m/z: calcd for C33H35BNO3+ ([M]+), 504.2705; found, 504.2702. 2488


ACS Omega

Article

9-[4′-(Trifluoroborato)phenyl)]-10-(4″-octyloxyphenyl)acridinium (8). A mixture of 5 (252 mg, 0.50 mmol) and KHF2 (390 mg, 2.5 mmol) in acetone (5 mL) and water (2 mL) was stirred for 2 h at room temperature. Then, it was evaporated to dryness under reduced pressure. The solid was extracted with acetone (3 × 10 mL). The combined extracts were concentrated and then Et2O (5 mL) was added to precipitate the product as a yellow powder, which was filtered and dried in vacuo, mp (dec) 145−150 °C. Yield 227 mg (86%). 1H NMR (400 MHz, CDCl3): δ 8.14 (d, J = 8.7 Hz, 2H), 8.12−8.03 (m, 2H), 7.68−7.54 (m, 8H), 7.35 (d, J = 8.8 Hz, 2H), 7.18 (d, J = 7.4 Hz, 2H), 4.17 (t, J = 6.4 Hz, 2H), 1.99−1.84 (m, 2H), 1.55 (d, J = 7.7 Hz, 2H), 1.50−1.23 (m, 8H), 0.91 (t, J = 6.1 Hz, 3H) ppm. 13C NMR (101 MHz, CDCl3): δ 165.68, 161.41, 142.55, 138.49, 138.37, 132.07, 130.99, 129.34, 129.20, 129.12, 128.44, 127.68, 126.05, 119.50, 117.03, 68.79, 31.79, 29.31, 29.22, 29.13, 26.04, 22.61, 13.98 ppm. 11B NMR (96 MHz, CDCl3): δ 9.2 ppm. 19F NMR (376 MHz, CDCl3): δ −144.98 ppm. HRMS (ESI) m/z: calcd for C33H33BF2NO ([M − F]+), 508.2618; found, 508.2616. 9-[3′-(Trifluoroborato)phenyl)]-10-(4″-octyloxyphenyl)acridinium (9). This compound was obtained as described for 8 using 6 as a starting material. Yellow powder, mp (dec) 225− 228 °C. Yield 190 mg (73%). 1H NMR (400 MHz, acetoned6): δ 8.33−8.26 (m, 2H), 8.24−8.18 (m, 2H), 7.96−7.87 (m, 2H), 7.82−7.74 (m, 4H), 7.64 (s, 1H), 7.52−7.49 (m, 2H), 7.30 (d, J = 7.4 Hz, 1H), 4.28 (t, J = 6.5 Hz, 2H), 2.00−1.87 (m, 2H), 1.65−1.57 (m, 2H), 1.53−1.29 (m, 8H), 0.91 (t, J = 6.1 Hz, 3H). 13C NMR (101 MHz, acetone-d6): δ 167.12, 162.22, 143.75, 139.16, 135.03, 134.34, 131.44, 130.32, 130.19, 128.46, 127.30, 127.21, 127.05, 120.56, 117.70, 69.47, 32.59, 30.09, 29.94, 26.82, 23.34, 14.38. 11B NMR (96 MHz, acetoned6): δ 7.5 ppm. 19F NMR (376 MHz, acetone-d6): δ −143.33 ppm. HRMS (ESI) m/z: calcd for C33H33BF2NO ([M − F]+), 508.2618; found, 508.2611. 9-[2′-(Trifluoroborato)phenyl)]-10-(4″-octyloxyphenyl)acridinium (10). This compound was obtained as described for 8 using 7 as a starting material. Yellow powder, mp (dec) 136−139 °C. Yield 235 mg (89%). 1H NMR (400 MHz, CDCl3): δ 8.19 (d, J = 8.7, 1.0 Hz, 2H), 8.11 (d, J = 7.3 Hz, 1H), 7.95 (ddd, J = 9.0, 6.8, 1.4 Hz, 2H), 7.63−7.53 (m, 3H), 7.48−7.41 (m, 3H), 7.39−7.34 (m, 2H), 7.33−7.28 (m, 2H), 7.03 (d, J = 7.5 Hz, 1H), 4.15 (t, J = 6.4 Hz, 2H), 2.01−1.79 (m, 2H), 1.62−1.49 (m, 2H), 1.49−1.26 (m, 8H), 0.92 (t, J = 6.4 Hz, 3H) ppm. 13C NMR (101 MHz, CDCl3): δ 172.25, 161.23, 141.74, 137.95, 133.61 (q, J = 2 Hz), 132.69, 129.22, 129.17, 128.80, 128.72, 127.25, 126.86, 126.52, 125.37, 118.31, 117.06, 116.82, 68.89, 31.83, 29.35, 29.26, 29.15, 26.07, 22.69, 14.14 ppm. 11B NMR (96 MHz, CDCl3): δ 2.6 ppm. 19F NMR (376 MHz): δ −139.22 ppm. HRMS (ESI) m/z: calcd for C33H33BF2NO ([M − F]+), 508.2618; found, 508.2616. Photocatalytic Reactions. Iodoperfluorobutylation of ethynyl MIDA-boronate catalyzed by 5−10: ethynyl MIDA boronate (0.543 g, 3.0 mmol, 1 equiv), nonafluoro-1iodobutane (1.380 g, 4.0 mmol), (+)-sodium L-ascorbate (0.2 g, 1.0 mmol, 0.33 equiv), and the photocatalyst 5−7 (36 mg, 2% mol) or 8−10 (32 mg, 2% mol) were dissolved in degassed dimethyl sulfoxide (DMSO) (10 mL) at RT. The reaction flask was placed approx. 2 cm from a blue LED light strip and stirred. After 24 h, the mixture was diluted with 25 mL of CH2Cl2, filtered, and washed with water (3 × 10 mL). The CH2Cl2 layer was dried over anhydrous MgSO4, filtered, and allowed to evaporate. The crude product was washed with

Et2O and dried; yield (the main isomer) 0.71 g (45%) for 5−8, 0.87 g (55%) for 10, mp 164−165 °C; the spectra are in agreement with the reported data:58 1H NMR (300 MHz, DMSO-d6): δ 7.18 (t, J = 15 Hz, 1H, HCC), 4.43 (d, J = 18 Hz, 2H, CH2), 4.12 (d, J = 18 Hz, 2H, CH2), 2.89 (s, 3H, CH3); 13C{1H} NMR (100.6 MHz, DMSO-d6): 168.30, 130.23 (t, J = 22 Hz), 63.34, 46.71 ppm; 19F NMR (376.2 MHz, DMSO-d6) −80.59 (t, J = 11 Hz, 3F), −108.87 (q, J = 11 Hz, 2F), −123.38 (q, J = 11 Hz, 2F), −125.59 (t, J = 11 Hz, 2F) ppm. Photocatalytic addition of methanol to diethyl ethylidenemalonate catalyzed by 5−7 or 10: diethyl ethylidenemalonate (0.56 g, 3.0 mmol, 1 equiv), methanol (3.2 g, 100 mmol), and the photocatalyst 5−7 (36 mg, 2% mol) or 10 (32 mg, 2% mol) were dissolved in acetone (10 mL) at RT and the reaction mixture was degassed by Ar sparging for 15 min. The reaction flask was placed approx. 2 cm from a blue LED light strip and stirred 24 h. After evaporation of volatiles, the reaction mixture was diluted with 10 mL of hexane and filtered off. The remaining solution was evaporated to give the colorless oily liquid which was analyzed by NMR which showed the formation of 12. 1H NMR (300 MHz, CDCl3): δ 4.26−4.16 (m, 4H, OCH2), 3.95 (dq, J = 9, 6 Hz, 1H, CH), 3.46 (d, J = 9 Hz, 1H, CH), 3.35 (s, 3H, OCH3), 1.28 (t, J = 6 Hz, 3H, CH3), 1.27 (t, J = 6 Hz, 3H, CH3), 1.26 (t, J = 6 Hz, 3H, CH3) ppm. Cyclic Voltammetry. CV measurements were carried out in a dry argon atmosphere using a VMP3 potentiostat (BioLogic) with a scan rate 0.1 V·s−1. The solutions of studied compounds (1 mM) in 0.1 M Bu4NPF6/CH2Cl2 were prepared inside the argon-filled glovebox and then measured in a three-electrode electrochemical cell: a gold working electrode (ALS Co. Ltd.; 2 mm2), a counter electrode (platinum wire), and an Ag/Ag+ reference electrode (silver wire in 0.1 M AgNO3/AN). The potential of the reference electrode versus the ferrocene redox couple was checked before and after experiments. X-ray Structural Measurements and Refinement Details. The single crystal of 9 was obtained by slow evaporation of acetone solution. It was measured at 100 K on a SuperNova diffractometer equipped with a Atlas detector (Cu Kα radiation, λ = 1.54184 Å). Data reduction and analysis were carried out with the CrysAlisPro program.63 All structures were solved by direct methods using SHELXS-9764 and refined using SHELXL-2014.65 Crystallographic information file (CIF) has been deposited with the Cambridge Crystallographic Data Centre as supplementary publications no. 1874040. Crystal data for 9: C33H33BF3NO, Mr = 527.41 au; orthorhombic; Fdd2; a = 24.1280(6) Å, b = 20.9554(5) Å, c = 21.3904(5) Å, V = 10815.2(5) Å3; dcalc = 1.296 g·cm−3; μ = 0.740 mm−1; Z = 16; F(000) = 4448; number of collected/ unique reflection (Rint = 3.20%) = 21 410/5480, R[F]/wR[F] (I ≥ 3σ(I)) = 3.39%/10.50%, Δ6(min/max) = −0.190/+0.239 e· res Å−3. Optical Properties. The UV−vis absorption spectra were recorded using a Hitachi UV-2300II spectrometer. The emission spectra were recorded using a Hitachi F-7000 spectrofluorometer, equipped with a photomultiplier detector, calibrated using Spectral Fluorescence Standard Kit certified by BAM Federal Institute for Materials Research and Testing.66 The measurements were performed at room temperature, according to published procedures.67,68 Suprasil quartz cuvettes (10.00 mm) were used. 1.5 nm slits were used for 2489


ACS Omega

Article

ORCID

absorption and 2.5 nm slits were used for emission spectra. To eliminate any background emission, the spectrum of a pure solvent was subtracted from the samples’ spectra. QY were determined in diluted solutions (A < 0.1 for longest wavelength band) by comparison with known standard coumarin 153 in ethanol (c = 4 × 10−6 mol·dm−3, QY = 0.544).66 Concentration of complexes solutions were in the range of 1−2 × 10−5 M (concentration was adjusted to reach similar absorbance to absorbance of reference solution at the excitation wavelength). To calculate the QY the following formula was used QYx = QYst ·

Krzysztof Durka: 0000-0002-6113-4841 Piotr Jankowski: 0000-0003-0178-8955 Sergiusz Luliński: 0000-0002-9635-5572 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by Warsaw University of Technology and by the National Science Centre, Poland (Narodowe Centrum Nauki, grant no. UMO-2015/19/D/ST5/00735). We would like to thank Prof. Krzysztof Woźniak from the Crystallographic Unit of the Physical Chemistry Laboratory (Chemistry Department, University of Warsaw) for providing access to X-ray diffraction facility. The authors also thank the Wrocław Centre for Networking and Supercomputing for providing access to computational facilities (grant number 285).

Fx 1 − 10−Ast n x 2 · · Fst 1 − 10−A x nst 2

where F is the relative integrated photon flux of sample (x) and standard (st), A is the absorbance at the excitation wavelength, and n is the refractive index of used solvents. F=

∫ Ic dλem = ∫

■

I(λem) dλem s(λem)

Photon fluxes (F) were calculated by integration of corrected spectra (Ic), obtained by division of intensity of emission spectra (I) by the spectral responsivity (s) at corresponding wavelengths (λem). All measurements were carried out at room temperature. Theoretical Calculations. The single-molecule optimizations were performed for all conformers of 1 and 2 at the PBE0/6-311+G(d,p)69−71 level of theory. The minima were confirmed by vibrational frequency calculations within harmonic approximation (no imaginary frequencies). During the calculations, no symmetry constraints were applied. The initial geometry of 9 was extracted from the crystal structures, and then the OC8H18 group was replaced by OEt group. Such a transformation did not affect the studied electronic processes but significantly simplified the calculations. The remaining structures were generated by changing the substitution pattern. In the case of 5−7, the ClO4− anion first was placed apart from the acridinium cation; during the optimization procedure, it approached close to the cation. The cartesian coordinates for optimized structures are given in Tables S4−S9 in the Supporting Information. Excited-state geometries, along with absorption and emission spectra, were obtained using TD-DFT methods with the same basis set, starting with geometries obtained from ground-state optimizations.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b03290.

■

REFERENCES

(1) Schmidt, A.; Liu, M. Recent Advances in the Chemistry of Acridines. Adv. Heterocycl. Chem. 2015, 115, 287−353. (2) Cholewiński, G.; Dzierzbicka, K.; Kołodziejczyk, A. M. Natural and synthetic acridines/acridones as antitumor agents: their biological activities and methods of synthesis. Pharmacol. Rep. 2011, 63, 305− 336. (3) Kasama, K.; Kikuchi, K.; Nishida, Y.; Kokubun, H. Deactivation mechanism of excited acridine and 9-substituted acridines in water. J. Phys. Chem. 1981, 85, 4148−4153. (4) Kikuchi, K.; Hattori, Y.; Sato, C.; Kokubun, H. Deactivation mechanism of photoexcited 9-phenylacridine in methanol. J. Phys. Chem. 1990, 94, 4039−4042. (5) Jones, G., II; Farahat, M. S.; Greenfield, S. R.; Gosztola, D. J.; Wasielewski, M. R. Ultrafast photoinduced charge-shift reactions in electron donor-acceptor 9-arylacridinium ions. Chem. Phys. Lett. 1994, 229, 40−46. (6) van Willigen, H.; Jones, G., II; Farahat, M. S. Time-Resolved EPR Study of Photoexcited Triplet-State Formation in ElectronDonor-Substituted Acridinium Ions. J. Phys. Chem. 1996, 100, 3312− 3316. (7) Horng, M. L.; Dahl, K.; Jones, G.; Maroncelli, M. Electron transfer in a donor-substituted acridinium dye: evidence for dynamical solvent control. Chem. Phys. Lett. 1999, 315, 363−370. (8) Rubio-Pons, Ò .; Serrano-Andrés, L.; Merchán, M. A Theoretical Insight into the Photophysics of Acridine. J. Phys. Chem. A 2001, 105, 9664−9673. (9) Lappe, J.; Cave, R. J.; Newton, M. D.; Rostov, I. V. A Theoretical Investigation of Charge Transfer in Several Substituted Acridinium Ions†. J. Phys. Chem. B 2005, 109, 6610−6619. (10) Benniston, A. C.; Harriman, A. Charge on the move: how electron-transfer dynamics depend on molecular conformation. Chem. Soc. Rev. 2006, 35, 169−179. (11) Eberhard, J.; Peuntinger, K.; Fröhlich, R.; Guldi, D. M.; Mattay, J. Synthesis and Properties of Acridine and Acridinium Dye Functionalized Bis(terpyridine) Ruthenium(II) Complexes. Eur. J. Org. Chem. 2018, 2682−2700. (12) Yang, Y.-K.; Tae, J. Acridinium Salt Based Fluorescent and Colorimetric Chemosensor for the Detection of Cyanide in Water. Org. Lett. 2006, 8, 5721−5723. (13) Lin, Y.-C.; Chen, C.-T. Acridinium Salt-Based Fluoride and Acetate Chromofluorescent Probes: Molecular Insights into Anion Selectivity Switching. Org. Lett. 2009, 11, 4858−4861. (14) Martí-Centelles, V.; Burguete, M. I.; Galindo, F.; Izquierdo, M. A.; Kumar, D. K.; White, A. J. P.; Luis, S. V.; Vilar, R. Fluorescent Acridine-Based Receptors for H2PO4−. J. Org. Chem. 2012, 77, 490− 500.

Copies of 1H and 13C NMR spectra of compounds 1− 10, additional information on optical properties and details of theoretical calculations, and TGA and DSC plots as well as ESI HRMS spectra of compounds 5−10 (PDF) X-ray structural data for compound 9 (CIF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. 2490


ACS Omega

Article

(15) Gosset, A.; Xu, Z.; Maurel, F.; Chamoreau, L.-M.; Nowak, S.; Vives, G.; Perruchot, C.; Heitz, V.; Jacquot de Rouville, H.-P. A chemically-responsive bis-acridinium receptor. New J. Chem. 2018, 42, 4728−4734. (16) Weeks, I.; Beheshti, I.; McCapra, F.; Campbell, A. K.; Woodhead, J. S. Acridinium Esters as High-Specific-Activity Labels in Immunoassay. Clin. Chem. 1983, 29, 1474−1479. (17) Kuruvilla, E.; Ramaiah, D. Selective Interactions of a Few Acridinium Derivatives with Single Strand DNA: Study of Photophysical and DNA Binding Interactions. J. Phys. Chem. B 2007, 111, 6549−6556. (18) Scarano, W.; Lu, H.; Stenzel, M. H. Boronic acid ester with dopamine as a tool for bioconjugation and for visualization of cell apoptosis. Chem. Commun. 2014, 50, 6390−6393. (19) Vezzu, D. A. K.; Deaton, J. C.; Shayeghi, M.; Huo, S. Acridinone/Amine(carbazole)-Based Bipolar Molecules: Efficient Hosts for Fluorescent and Phosphorescent Emitters. Org. Lett. 2009, 11, 4310−4313. (20) Méhes, G.; Nomura, H.; Zhang, Q.; Nakagawa, T.; Adachi, C. Enhanced Electroluminescence Efficiency in a Spiro-Acridine Derivative through Thermally Activated Delayed Fluorescence. Angew. Chem., Int. Ed. 2012, 51, 11311−11315. (21) Reddy, S. S.; Sree, V. G.; Gunasekar, K.; Cho, W.; Gal, Y.-S.; Song, M.; Kang, J.-W.; Jin, S.-H. Highly Efficient Bipolar Deep-Blue Fluorescent Emitters for Solution-Processed Non-Doped Organic Light-Emitting Diodes Based on 9,9-Dimethyl-9,10-dihydroacridine/ Phenanthroimadazole Derivatives. Adv. Opt. Mater. 2016, 4, 1236− 1246. (22) Braveenth, R.; Bae, I.-J.; Wang, Y.; Kim, S.; Kim, M.; Chai, K. Acridine-Triphenylamine Based Hole-Transporting and Hole-Injecting Material for Highly Efficient Phosphorescent-Based Organic Light Emitting Diodes. Appl. Sci. 2018, 8, 1168. (23) Cho, A.-N.; Chakravarthi, N.; Kranthiraja, K.; Reddy, S. S.; Kim, H.-S.; Jin, S.-H.; Park, N.-G. Acridine-based novel hole transporting material for high efficiency perovskite solar cells. J. Mater. Chem. A 2017, 5, 7603−7611. (24) Natrajan, A.; Wen, D.; Sharpe, D. Synthesis and properties of chemiluminescent acridinium ester labels with fluorous tags. Org. Biomol. Chem. 2014, 12, 3887−3901. (25) Nakazono, M.; Oshikawa, Y.; Nakamura, M.; Kubota, H.; Nanbu, S. Strongly Chemiluminescent Acridinium Esters under Neutral Conditions: Synthesis, Properties, Determination, and Theoretical Study. J. Org. Chem. 2017, 82, 2450−2461. (26) Nakazono, M.; Nanbu, S. Enhancement effect on the chemiluminescence of acridinium esters under neutral conditions. Luminescence 2017, 33, 345−348. (27) Grubert, L.; Hennig, H.; Abraham, W. Photo, proton and metal ion responsive wide-rim acridane substituted calix[4]arenes. Tetrahedron 2009, 65, 5936−5944. (28) Vetter, A.; Abraham, W. Controlling Ring Translation of Rotaxanes. Org. Biomol. Chem. 2010, 8, 4666−4681. (29) Ackmann, A. J.; Fréchet, J. M. J. The generation of hydroxide and methoxide ions by photo-irradiation: use of aromatization to stabilize ionic photo-products from acridine derivatives. Chem. Commun. 1996, 605−606. (30) Zhou, D.; Khatmullin, R.; Walpita, J.; Miller, N. A.; Luk, H. L.; Vyas, S.; Hadad, C. M.; Glusac, K. D. Mechanistic Study of the Photochemical Hydroxide Ion Release from 9-Hydroxy-10-methyl-9phenyl-9,10-dihydroacridine. J. Am. Chem. Soc. 2012, 134, 11301− 11303. (31) Ohkubo, K.; Fukuzumi, S. 100% Selective Oxygenation of pXylene to p-Tolualdehyde via Photoinduced Electron Transfer. Org. Lett. 2000, 2, 3647−3650. (32) Suga, K.; Ohkubo, K.; Fukuzumi, S. Oxygenation of αMethylstyrene with Molecular Oxygen, Catalyzed by 10-Methylacridinium Ion via Photoinduced Electron Transfer. J. Phys. Chem. A 2003, 107, 4339−4346. (33) Suga, K.; Ohkubo, K.; Fukuzumi, S. Selective Oxygenation of 4,4’-Dimethylbiphenyl with Molecular Oxygen, Catalyzed by 9-

Phenyl-10-methylacridinium Ion via Photoinduced Electron Transfer. J. Phys. Chem. A 2005, 109, 10168−10175. (34) Ohkubo, K.; Suga, K.; Fukuzumi, S. Solvent-free selective photocatalytic oxidation of benzyl alcohol to benzaldehyde by molecular oxygen using 9-phenyl-10-methylacridinium. Chem. Commun. 2006, 2018−2020. (35) Fang, X.; Liu, Y.-C.; Li, C. 9-Phenyl-10-methylacridinium: A Highly Efficient and Reusable Organocatalyst for Mild Aromatization of 1,4-Dihydropyridines by Molecular Oxygen. J. Org. Chem. 2007, 72, 8608−8610. (36) Griesbeck, A. G.; Cho, M. 9-Mesityl-10-methylacridinium: An Efficient Type II and Electron-Transfer Photooxygenation Catalyst. Org. Lett. 2007, 9, 611−613. (37) Ohkubo, K.; Fujimoto, A.; Fukuzumi, S. Metal-free oxygenation of cyclohexane with oxygen catalyzed by 9-mesityl-10-methylacridinium and hydrogen chloride under visible light irradiation. Chem. Commun. 2011, 47, 8515−8517. (38) Ohkubo, K.; Mizushima, K.; Iwata, R.; Fukuzumi, S. Selective photocatalytic aerobic bromination with hydrogen bromide via an electron-transfer state of 9-mesityl-10-methylacridinium ion. Chem. Sci. 2011, 2, 715−722. (39) Wilger, D. J.; Gesmundo, N. J.; Nicewicz, D. A. Catalytic hydrotrifluoromethylation of styrenes and unactivated aliphatic alkenes via an organic photoredox system. Chem. Sci. 2013, 4, 3160−3165. (40) Romero, N. A.; Nicewicz, D. A. Mechanistic Insight into the Photoredox Catalysis of Anti-Markovnikov Alkene Hydrofunctionalization Reactions. J. Am. Chem. Soc. 2014, 136, 17024−17035. (41) Wilger, D. J.; Grandjean, J.-M. M.; Lammert, T. R.; Nicewicz, D. A. The Direct Anti-Markovnikov Addition of Mineral Acids to Styrenes. Nat. Chem. 2014, 6, 720−726. (42) Gesmundo, N. J.; Grandjean, J.-M. M.; Nicewicz, D. A. Amide and Amine Nucleophiles in Polar Radical Crossover Cycloadditions: Synthesis of γ-Lactams and Pyrrolidines. Org. Lett. 2015, 17, 1316− 1319. (43) Joshi-Pangu, A.; Lévesque, F.; Roth, H. G.; Oliver, S. F.; Campeau, L.-C.; Nicewicz, D.; DiRocco, D. A. Acridinium-Based Photocatalysts: A Sustainable Option in Photoredox Catalysis. J. Org. Chem. 2016, 81, 7244−7249. (44) Romero, N. A.; Nicewicz, D. A. Organic Photoredox Catalysis. Chem. Rev. 2016, 116, 10075−10166. (45) Crespin, L. N. S.; Greb, A.; Blakemore, D. C.; Ley, S. V. VisibleLight-Mediated Annulation of Electron-Rich Alkenes and NitrogenCentered Radicals from N-Sulfonylallylamines: Construction of Chloromethylated Pyrrolidine Derivatives. J. Org. Chem. 2017, 82, 13093−13108. (46) Wang, L.; Wu, F.; Chen, J.; Nicewicz, D. A.; Huang, Y. VisibleLight-Mediated [4+2] Cycloaddition of Styrenes: Synthesis of Tetralin Derivatives. Angew. Chem., Int. Ed. 2017, 56, 6896−6900. (47) Tay, N. E. S.; Nicewicz, D. A. Cation Radical Accelerated Nucleophilic Aromatic Substitution via Organic Photoredox Catalysis. J. Am. Chem. Soc. 2017, 139, 16100−16104. (48) Wu, F.; Wang, L.; Chen, J.; Nicewicz, D. A.; Huang, Y. Direct Synthesis of Polysubstituted Aldehydes via Visible-Light Catalysis. Angew. Chem., Int. Ed. 2018, 57, 2174−2178. (49) Zhou, W.; Miura, T.; Murakami, M. Photocatalyzed ortho -Alkylation of Pyridine N -Oxides through Alkene Cleavage. Angew. Chem., Int. Ed. 2018, 57, 5139−5142. (50) Rondeau-Gagné, S.; Curutchet, C.; Grenier, F.; Scholes, G. D.; Morin, J.-F. Synthesis, characterization and DFT calculations of new ethynyl-bridged C60 derivatives. Tetrahedron 2010, 66, 4230−4242. (51) Dąbrowski, M.; Kurach, P.; Luliński, S.; Serwatowski, J. Anortho-lithiated derivative of protected phenylboronic acid: an approach toortho-functionalized arylboronic acids and 1,3-dihydro-1hydroxybenzo[c][2,1]oxaboroles. Appl. Organomet. Chem. 2007, 21, 234−238. (52) Oliveira, R. A.; Silva, R. O.; Molander, G. A.; Menezes, P. H. 1 H, 13C, 19F and 11B NMR spectral reference data of some potassium organotrifluoroborates. Magn. Reson. Chem. 2009, 47, 873−878. 2491


ACS Omega

Article

(53) Benniston, A. C.; Harriman, A.; Li, P.; Rostron, J. P.; van Ramesdonk, H. J.; Groeneveld, M. M.; Zhang, H.; Verhoeven, J. W. Charge Shift and Triplet State Formation in the 9-Mesityl-10methylacridinium Cation. J. Am. Chem. Soc. 2005, 127, 16054−16064. (54) Rurack, K.; Spieles, M. Fluorescence Quantum Yields of a Series of Red and Near-Infrared Dyes Emitting at 600−1000 nm. Anal. Chem. 2011, 83, 1232−1242. (55) Fukuzumi, S.; Kotani, H.; Ohkubo, K.; Ogo, S.; Tkachenko, N. V.; Lemmetyinen, H. Electron-Transfer State of 9-Mesityl-10methylacridinium Ion with a Much Longer Lifetime and Higher Energy Than That of the Natural Photosynthetic Reaction Center. J. Am. Chem. Soc. 2004, 126, 1600−1601. (56) Zilberg, S. Electronic structure of 9-mesityl-10-methylacridinium in ground and excited states: charge-shift mechanism introduced by counter anion shift. Phys. Chem. Chem. Phys. 2010, 12, 10292− 10294. (57) Hu, J.; Xia, B.; Bao, D.; Ferreira, A.; Wan, J.; Jones, G., II; Vullev, V. I. Long-Lived Photogenerated States of α-Oligothiophene− Acridinium Dyads Have Triplet Character. J. Phys. Chem. A 2009, 113, 3096−3107. (58) Kublicki, M.; Dąbrowski, M.; Durka, K.; Kliś, T.; Serwatowski, J.; Woźniak, K. Visible-light-promoted alkylation of unsaturated MIDA boronates using Ru(bpy)3Cl2 as the photoredox catalyst. Tetrahedron Lett. 2017, 58, 2162−2165. (59) Wallentin, C.-J.; Nguyen, J. D.; Finkbeiner, P.; Stephenson, C. R. J. Visible Light-Mediated Atom Transfer Radical Addition via Oxidative and Reductive Quenching of Photocatalysts. J. Am. Chem. Soc. 2012, 134, 8875−8884. (60) Xu, H. J.; Xu, X. L.; Fu, Y.; Feng, Y. S. Photocatalytic Oxidation of Primary and Secondary Benzyl Alcohol Catalyzed by Two Coenzyme NAD+ Models. Chin. Chem. Lett. 2007, 18, 1471−1475. (61) Sawyer, D. T.; Chiericato, G.; Angelis, C. T.; Nanni, E. J.; Tsuchiya, T. Effects of media and electrode materials on the electrochemical reduction of dioxygen. Anal. Chem. 1982, 54, 1720−1724. (62) Chinzei, T.; Miyazawa, K.; Yasu, Y.; Koike, T.; Akita, M. Redox-economical radical generation from organoborates and carboxylic acids by organic photoredox catalysis. RSC Adv. 2015, 5, 21297−21300. (63) CrysAlis Pro Software; Oxford Diffraction Ltd.: Oxford, U.K., 2010. (64) Sheldrick, G. M. A short history ofSHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2007, 64, 112−122. (65) Sheldrick, G. M. Crystal structure refinement withSHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8. (66) Pfeifer, D.; Hoffmann, K.; Hoffmann, A.; Monte, C.; ReschGenger, U. The Calibration Kit Spectral Fluorescence Standards-A Simple and Certified Tool for the Standardization of the Spectral Characteristics of Fluorescence Instruments. J. Fluoresc. 2006, 16, 581−587. (67) Würth, C.; Grabolle, M.; Pauli, J.; Spieles, M.; Resch-Genger, U. Relative and absolute determination of fluorescence quantum yields of transparent samples. Nat. Protoc. 2013, 8, 1535−1550. (68) Resch-Genger, U.; Rurack, K. Determination of the photoluminescence quantum yield of dilute dye solutions (IUPAC Technical Report). Pure Appl. Chem. 2013, 85, 2005−2013. (69) Adamo, C.; Barone, V. Toward reliable density functional methods without adjustable parameters: The PBE0 model. J. Chem. Phys. 1999, 110, 6158−6170. (70) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. Selfconsistent molecular orbital methods. XX. A basis set for correlated wave functions. J. Chem. Phys. 1980, 72, 650−654. (71) Lee, C.; Yang, W.; Parr, R. G. Development of the ColleSalvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789.

2492


Cationic and Betaine-Type Boronated Acridinium Dyes: Synthesis

Recommend Documents