Cyclotriphosphazene cored naphthalimide-BODIPY dendrimeric systems: Synthesis, photophysical and antimicrobial properties

Journal Pre-proofs Research paper Cyclotriphosphazene Cored Naphtalimide-BODIPY Dendrimeric Systems: Synthesis, Photophysical and Antimicrobial Properties Elif Şenkuytu, Ezel Öztürk, Fatma Aydinoğlu, Esra Taniverdi Eçik, Elif Okutan PII: DOI: Reference:

S0020-1693(19)31759-1 https://doi.org/10.1016/j.ica.2019.119386 ICA 119386

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Inorganica Chimica Acta

Received Date: Revised Date: Accepted Date:

14 November 2019 17 December 2019 17 December 2019

Please cite this article as: E. Şenkuytu, E. Öztürk, F. Aydinoğlu, E. Taniverdi Eçik, E. Okutan, Cyclotriphosphazene Cored Naphtalimide-BODIPY Dendrimeric Systems: Synthesis, Photophysical and Antimicrobial Properties, Inorganica Chimica Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.119386

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Cyclotriphosphazene Cored Naphtalimide-BODIPY Dendrimeric Systems: Synthesis, Photophysical and Antimicrobial Properties

Elif ŞENKUYTUa, Ezel ÖZTÜRKa, Fatma AYDINOĞLUb, Esra TANIVERDİ EÇİKc, Elif OKUTANa*

a

Department of Chemistry, Faculty of Science, Gebze Technical University, Gebze, Kocaeli,

Turkey b

Department of Molecular Biology and Genetics, Faculty of Science, Gebze Technical

University, Gebze, Kocaeli, Turkey c Department of Chemistry,

*Author

Faculty of Science, Ataturk University, Yakutiye, Erzurum, Turkey

for correspondence:

Dr. Elif OKUTAN, Department of Chemistry, Gebze Technical University, P.O.Box: 141, Gebze 41400, Kocaeli, Turkey Tel:

00 90 262 6053091

Fax:

00 90 262 6053105

e-mail:

[email protected]

Abstract

In this work, we report the synthesis and characterization of novel fluorescent naphthylamide (NI)-boron dipyrromethene (BODIPY) dyads and dendrimeric triad systems, based on NI functionalized mono- and distyryl- boron BODIPY derivatives with cyclotriphosphazene core. The structures of new dyads and triad systems were characterized by 1H, 13C and 31P NMR. Spectroscopic properties including absorption, emission profiles, fluorescence quantum yield and fluorescence lifetime of NI-BODIPY dyads and NI-BODIPY-cyclotriphosphazene triads were investigated via UV-Vis absorption and fluorescence emission (2D and 3D) techniques. The NI groups on BODIPYs 3- and 5- positions procure the red-shift in absorption and emission spectra compared to BODIPY core. The energy transfer process inhibited the emission of NI moiety and induced the fluorescence from BODIPY unit. The dendrimeric mono- and di-styryl NI-BODIPY-cyclotriphosphazene systems (7 and 8) presented intense absorption bands about 570 and 639 nm respectively both exciting from NI and BODIPY subunits. Also, the triad systems (7 and 8) were screened against Gram-positive and Gram-negative bacterial strains. The results demonstrated that naphtalimide-BODIPY-cyclotriphosphazene triads had an antimicrobial activity against Gram-positive Staphylococcus aureus.

Keywords: BODIPY, cyclotriphosphazene, naphtalimide, photophyisical

1. Introduction Organic and inorganic ring systems represent prevailing branch of chemistry in which a series of atoms bonded to form varied size ring. Within this family of compounds, the chlorocyclophosphazenes received maximum attention as inorganic ring system [1-3]. The development of phosphazenes chemistry flourished around nucleophilic substitution reactions and the polymerization of cyclophosphazenes and investigation of properties and potential applications of these constructions [4]. Especially the ease of the substitution reactions of the chlorines, attached to the phosphorus atoms allow the construction of multimodular systems which can be easily obtained by various nucleophiles [5]. It also offers advantageous to utilize in the aimed application where parameters such as physical and chemical against various influences can be controlled. A wide set of functional groups can be attached to the phosphazene core, allowing many possibilities including further derivatization [6]. These facilities allow the preparation of a diverse phosphazene cored dendritic constructs decorated with different fineries such as chromophores (BODIPY, phthalocyanines and perylene etc.) for their photophysical properties [7-9]. Among these chromophores boron-dipyrromethane derivatives (BODIPYs) and naphthalimides (NI) are two of the fluorophores that demonstrate excellent photophysical properties. Therefore, many applications are accredited to these molecules, in a vide variety of scientific fields which include biological, molecular imaging, phototheranostics, electroluminescent devices, construction of organic light emitting diodes (OLED) and photovoltaic cells etc. [10-16]. The ease and wide scope of the modifications around BODIPY core and naphthalimides are made possible aforementioned applications. Especially many studies were focused on the preperation of various NI or BODIPY compounds as potential antimicrobial agents [17-21]. Also the design and preparation of dyad, triad and tetrad type polychromophore systems are popular among scientific community since it provide the opportunity to use individual properties of the chromophores in a single system [22-24]. Linking of fluorophores in multichromophoric systems can be accomplished via various strategies and connection units can be either aliphatic chains or conjugated moieties. Energy transfer between these systems is crucial for many applications such as solar energy conversion, fluorescent sensors and biological systems in which energy is harvested by one molecular antennae and funnelled to the secondary chromophore as acceptor [25, 26]. The aim of this study is the development of new NI-BODIPYcyclotriphosphazene triads (7 and 8). The designed dendrimeric structures consists of two fluorophore (NI and BODIPY)

moieties, a cyclotriphosphazene core (Scheme 1). We reported the synthesis, characterization, photophysical properties and antimicrobial activities of two mono- and distyryl-BODIPY substituted cyclotriphosphazene derivative in which BODIPY is functionalized at the C3 and/or C6 positions by a NI group. The presence of NI on BODIPY units significantly changed their photophysical properties. Moreover antimicrobial activities of two novel NI-BODIPYcyclotriphosphazenes were explored.

2. Experimental 2.1. Materials The deuterated solvent (CDCl3) for NMR spectroscopy, silica gel, dichloromethane, N,Ndimethylformamide, benzene, methanol, trimethylamine, piperidine and sodium hydride were provided from Merck. Following chemicals were obtained from Sigma Aldrich; sodium ascorbate and copper (II) sulfate pentahydrate. 2.2. Equipment Electronic absorption spectra were recorded with a Shimadzu 2101 UV spectrophotometer in the UV-visible region. Fluorescence excitation and emission spectra were recorded on a Varian Eclipse spectrofluorometer using 1.0 cm pathlength cuvettes at room temperature. The fluorescence lifetimes were obtained using Horiba- Jobin- Yvon- SPEX Fluorolog 3-2iHR instrument with Fluoro Hub-B Single Photon Counting Controller. Signal acquisition was performed using a TCSPC module. Mass spectra were acquired in linear modes with average of 50 shots on a Bruker Daltonics Microflex mass spectrometer (Bremen, Germany) equipped with a nitrogen UV- Laser operating at 337 nm.1H, 31P and 13C NMR spectra were recorded in CDCl3 solutions on a Varian 500 MHz spectrometer. Analytical thin layer chromatography (TLC) was performed on silica gel plates (Merck, Kieselgel 60 Å, 0.25 mm thickness) with F254 indicator. Column chromatography was performed on silica gel (Merck, Kieselgel 60 Å, 230400 mesh). Suction column chromatography was performed on silica gel (Merck, Kieselgel 60 Å, 70-230 mesh). 2.3. The parameters for fluorescence quantum yields The fluorescence quantum yields (ΦF) of the compounds 4, 5, 7 and 8 were determined by the comparative method (Eq. (1)) [27].

𝐹.𝐴𝑆𝑡𝑑.𝑛2

∅𝐹 = ∅𝐹𝑆𝑡𝑑𝐹

2 𝑆𝑡𝑑.𝐴.𝑛𝑆𝑡𝑑

(1)

where F and FStd are the areas under the fluorescence emission curves of the compounds (4, 5, 7 and 8) and the standard, respectively. A and AStd are the respective absorbances of the compounds and the standard at the excitation wavelengths, respectively. The refractive indices (n) of the solvents were employed in calculating the fluorescence quantum yields in different solvents. Rhodamine B and unsubstituted ZnPc were employed as the standards (ΦF = 0.50 in ethanol for Rhodamine B and ΦF = 0.20 in DMSO for ZnPc) [28, 29].

2.4. Qualitative screening of the antimicrobial activity The materials were screened for their antimicrobial activities against Gram-positive (Staphylococcus aureus ATCC 25923) and Gram-negative (Escherichia coli ATCC 35218) bacteria by Kirby-Bauer disk diffusion susceptibility test protocol [30]. Kanamycin (10.0 µg) were used as standard antimicrobial controls for comparison. The solutions have been prepared in DMSO. Gram-negative and Gram-positive bacteria were grown in nutrient broth and incubated at 37 °C for 24 h. The bacterial suspensions were adjusted to 105 colony forming units per milliliter (CFU/mL) after incubation. The testing microorganism suspensions were spread over the surface of the Mueller Hinton agar (MHA) plates. Subsequently the filter paper which was embedded by test chemical materials (100.0 µg) were placed to center of each defined division on agar plate. The diameter of the inhibition zone was measured in millimeters after 24 h of incubation at 37 C. The experiment was made for twice, and the mean values were calculated.

3. Synthesis Compounds 1 [31], 3 and 6 were synthesized according to the literature (Scheme 1) [7].

3.1. Synthesis of compound 2 Compound 1 (1.0 g, 3.0 mmol) was dissolved in DMF (20.0 mL) under argon atm. and 4hydroxybenzaldehyde (0.44 g, 3.6 mmol) was added. After stirring for 15 min, anhydrous

potassium carbonate (0.5 g, 3.6 mmol) was added to the reaction mixture. The reaction mixture was refluxed at 100 ºC for 12 h. The reaction was followed by TLC. DMF was removed by vacuum distillation from the reaction mixture. Then, Compound 2 was purified by silica gel column chromatography using DCM (230-400 mesh) (yield: 47%). Spectral data of 2: MS (MALDI-TOF) (DIT) (m/z): Calc.:373.41; found: 373.188 [M]+ (Fig. S1). 1H-NMR (500 MHz, CDCl3, 293 K, δ ppm): 10.02 (s, 1H), 8.67 (d, J = 7.2 Hz, 1H), 8.55 (t, J = 9.1 Hz, 2H), 7.99 (d, J = 8.5 Hz, 2H), 7.79 (t, J = 7.8 Hz, 1H), 7.28 (d, J = 8.2 Hz, 2H), 7.14 (d, J = 8.1 Hz, 1H), 4.19 (t, J = 7.6 Hz, 2H), 1.73 (dd, J =15 Hz, J =7.43 Hz, 2H), 1.501.43 (m, 2H), 0.99 (t, J = 7.3, Hz, 3H) (Fig.S2).

13C-NMR

(126 MHz, CDCl3, 293 K, δ ppm):

190.62, 164.22, 163.61, 160.98, 157.65, 133.22, 132.46, 132.34, 132.14, 129.89, 128.25, 127.15, 124.57, 123.05, 119.89, 118.56, 113.59, 53.56, 40.38, 30.35, 20.51, 13.97 (Fig. S3).

3.2. Synthesis of compound 4 and 5 Compound 3 (0.15 g, 0.34 mmol) and compound 2 (0.29 g, 0.78 mmol) dissolved in benzene (60 mL). Piperidine (0.30 mL) and glacial acetic acid (0.30 mL) were added. The solution was refluxed using Dean- Stark apparatus. When the solution was concentrated, reaction was followed by TLC until dark pink-colored and dark blue-colored products became the major products. Compound 4 and 5 were purified by silica gel column chromatography using DCM:MeOH (98:2) (230-400 mesh) (yield: 24% for compound 4 and 36% for compound 5). Spectral data of 4: MS (MALDI-TOF) (DIT) (m/z): Calc.: 792.69; found: 792.146 [M]+ (Fig. S4). 1H NMR (500 MHz, CDCl3, 293 K, δ ppm): 8.70 (d, J= 7.21 Hz, 1H), 8.68 (d, J= 6.27 Hz, 1H), 8.51 (d, J= 8.2 Hz, 1H), 7.81 (t, J= 7.9 Hz, 1H), 7.72–7.69 (m, 3H), 7.25 (d, J= 16.89 Hz, 1H), 7.21 (d, J= 8.59 Hz, 2H), 7.19 (d, J= 8.77 Hz, 2H), 7.04 (d, J= 8.91 Hz, 2H), 7.01 (d, J= 8.75 Hz, 1H), 6.64 (s, 1H), 6.05 (s, 1H), 4.21 (t, J= 7.48 Hz, 2H), 4.08 (t, J= 5.75 Hz, 2H), 3.43 (t, J= 6.65 Hz, 2H), 2.62 (s, 3H), 1.98-1.93 (m, 2H), 1.89-1.86 (m, 4H), 1.78-1.72 (m, 2H), 1.61 (s, 3H), 1.52 (s, 3H), 1.00 (t, J= 7.3 Hz, 3H) (Fig. S5). 13C NMR (126 MHz, CDCl3, 293 K, δ ppm): 164.39, 163.75, 159.52, 159.40, 156.02, 155.34, 151.79, 143.51, 142.29, 140.84, 134.13, 134.07, 133.17, 132.72, 131.91, 129.74, 129.41, 129.31, 128.50, 127.10, 126.60, 124.05, 122.76, 121.57, 120.82, 119.65, 117.34, 117.05, 111.21, 67.98, 67.33, 51.22, 40.20, 30.27, 26.53, 25.78, 25.62, 20.41, 14.83, 14.79, 14.69, 13.87 (Fig. S6).

Spectral data of 5: MS (MALDI-TOF) (DIT) (m/z): Calc.:1148.07; found: 1145.687 [M-2H]+ (Fig. S7). 1H NMR (500 MHz, CDCl3, 293 K, δ ppm): 8.69 (d, J= 8.04 Hz, 2H), 8.67 (d, J= 6.79 Hz, 2H), 8.47 (d, J= 8.21 Hz, 2H), 7.78 (t, J= 7.82 Hz, 2H), 7.73–7.70 (m, 6H), 7.29 (d, J= 16.47 Hz, 2H), 7.23 (d, J= 8.13 Hz, 2H), 7.19 (d, J= 8.13 Hz, 4H), 7.03 (d, J= 8.05 Hz, 2H), 6.99 (d, J= 8.23 Hz, 2H), 6.67 (s, 2H), 4.17 (t, J= 7.29 Hz, 4H), 4.07 (t, J= 5.52 Hz, 2H), 3.42 (t, J= 6.40 Hz, 2H), 1.96-1.93 (m, 2H), 1.87-1.84 (m, 2H), 1.74-1.68 (m, 4H), 1.58 (s, 6H), 1.47-1.42 (m, 4H), 0.97 (t, J= 7.22 Hz, 6H) (Fig. S8). 13C NMR (126 MHz, CDCl3, 293 K, δ ppm): 164.33, 164.29, 163.70, 159.54, 159.30, 155.45, 155.41, 152.19, 134.63, 134.04, 133.94, 132.65, 131.90, 129.73, 129.71, 129.59, 129.57, 129.40, 128.45, 128.42, 126.59, 124.01, 122.72, 120.84, 117.07, 115.05, 111.19, 67.33, 51.21, 40.19, 30.25, 26.53, 25.78, 20.39, 14.92, 13.86 (Fig. S9).

3.3. Synthesis of compound 7 Compound 4 (90.0 mg, 0.11 mmol) and compound 6 (8.8 mg, 0.02 mmol) were dissolved in 5.0 mL of DCM:MeOH (4:1). CuSO4.5H2O (7.0 mg) and sodium ascorbate (7.0 mg) were added to the mixture. Reaction mixture was stirred at room temperature for 24 h. Reaction was followed by TLC. Reaction mixture was extracted 3 times with DCM:water. Organic layer was dried over anhydrous sodium sulfate and concentrated on a rotary evaporator until the solvent was removed. Compound 7 was purified by silica gel column chromatography using DCM:MeOH (95:5) (230-400 mesh) (yield: 15%). Spectral data of compound 7: 1H NMR (500 MHz, CDCl3, 293 K, δ ppm): 8.70-8.67 (m, 12H), 8.50 (d, J= 8.26 Hz, 6H), 8.50 (t, J= 8.32 Hz, 6H), 7.71-7.66 (m, 18H), 7.61 (s, 6H), 7.24 (d, J= 16.33 Hz, 6H), 7.22-7.18 (m, 24H), 7.02-7.00 (m, 18H), 6.63 (s, 6H), 6.04 (s, 6H), 4.62 (s, 12H), 4.50 (t, J= 7.10 Hz, 12H), 4.20 (t, J= 7.50 Hz, 12H), 4.07 (t, J= 5.95 Hz, 12H), 2.61 (s, 18H), 2.23-2.17 (m, 12H), 1.92-1.85 (m, 24H), 1.77-1.73 (m, 12H), 1.51 (s, 18H), 1.48 (s, 18H), 1.00 (t, J= 7.37 Hz, 18H) (Fig. S10).

13C

NMR (126 MHz, CDCl3, 293 K, δ ppm): 164.39,

163.75, 159.39, 156.03, 155.34, 151.81, 145.33, 143.48, 142.28, 140.75, 134.11, 133.15, 132.72, 132.55, 131.91, 129.73, 129.45, 129.31, 128.50, 127.22, 126.60, 124.04, 122.74, 122.21, 121.59, 120.83, 119.63, 117.36, 117.05, 115.01, 111.20, 67.98, 67.03, 66.10, 58.43, 49.99, 40.20, 30.27, 27.29, 26.23, 25.62, 20.41, 14.85, 14.79, 14.71, 13.87 (Fig. S11). 31P NMR (202 MHz, CDCl3, 293 K, δ ppm): 30.0 (s, 3P) (Fig. S12). 3.4. Synthesis of compound 8

Compound 5 (200.0 mg, 0.17 mmol) and compound 6 (10.13 mg, 0.02 mmol) were dissolved in 5 mL of DCM:MeOH (4:1). CuSO4.5H2O (7.0 mg) and sodium ascorbate (7.0 mg) were added to the mixture. Reaction mixture was stirred at room temperature for 24 h. Reaction was followed by TLC. Reaction mixture was extracted 3 times with DCM:water. Organic layer was dried over anhydrous sodium sulfate and concentrated on a rotary evaporator until the solvent was removed. Compound 8 was purified by silica gel column chromatography using DCM:MeOH (95:5) (230-400 mesh) (yield:12%). Spectral data of compound 8: 1H NMR (500 MHz, CDCl3, 293 K, δ ppm): 8.67 (d, J= 7.80 Hz, 12H), 8.65 (d, J= 6.64 Hz, 12H), 8.48 (d, J= 8.25 Hz, 12H), 7.79 (t, J= 7.80 Hz, 12H), 7.75– 7.72 (m, 36H), 7.62 (s, 6H), 7.28 (d, J= 16.28 Hz, 22H), 7.24 (d, J= 8.48 Hz, 12H), 7.20 (d, J= 8.57 Hz, 24H), 7.03 (d, J= 8.53 Hz, 12H), 7.00 (d, J= 8.25 Hz, 12H), 6.68 (s, 12H), 4.63 (s, 12H), 4.51 (t, J= 7.08 Hz, 12H), 4.18 (t, J= 7.50 Hz, 24H), 4.08 (t, J= 5.94 Hz, 12H), 2.24-2.18 (m, 12H), 1.93-1.88 (m, 12H), 1.76-1.70 (m, 24H), 1.54 (s, 36H), 1.50-1.42 (m, 24H), 0.99 (t, J= 7.36 Hz, 36H) (Fig. S13).

13C

NMR (126 MHz, CDCl3, 293 K, δ ppm): 164.28, 163.65,

159.41, 159.27, 155.43, 152.21, 145.29, 142.45, 139.39, 134.66, 134.01, 133.89, 132.62, 131.86, 129.67, 129.62, 129.39, 128.42, 127.15, 126.57, 123.97, 122.68, 122.20, 120.85, 119.54, 117.80, 117.02, 114.98, 111.14, 67.96, 67.02, 66.09, 58.43, 49.97, 40.17, 30.23, 27.29, 26.22, 20.39, 14.94, 13.86 (Fig. S14). 31P NMR (202 MHz, CDCl3, 293 K, δ ppm): 22.5 (s, 3P) (Fig. S15).

4. Results and discussion 4.1. Synthesis and Characterization The synthesis of the hexa-BODIPY functionalized dendrimeric cyclotriphosphazene conjugates were previously discussed [7]. In this paper, we report for the first time the fabrication of dendrimeric three component NI-BODIPY-cyclotriphosphazene systems (7 and 8) (Scheme 1). NI and BODIPY dyes represent two special classes that demonstrates outstanding photophyisical properties [32, 33] whereas cyclotriphosphazenes are attracted attention as a class of stable inorganic compound to synthesize dendrimeric molecules [34]. Herein first, the NI derivative bearing aldehyde functional group (2) and BODIPY core (3) were synthesized according to the literature [7, 31]. Subsequently mono- and distyryl- NI-BODIPY derivatives (4 and 5) were synthesized by treatment of compound 2 and 3 by following standard method of Knoevenagel condensation. The cyclotriphosphazene derivative [7], as the core bearing six

propargyl units (6) were then reacted with NI-BODIPYs (4 and 5) to obtain NI-BODIPYcyclotriphosphazene triad systems (7 and 8). All synthesized products were purified by column chromatography and the structural qualities of naphthylamide functionalized BODIPY dyads (4 and 5) and dendrimeric NI-BODIPY-cyclotriphosphazene constructs (7 and 8) (Scheme 1) were successfully characterized via using spectroscopic techniques: 1H,13C NMR and 31P NMR. The comparisons of 1H and

13C

NMR patterns of compounds (7 and 8) with previously

published BODIPY-cyclotriphosphazenes showed parallel disappearance and occurrence of protons/carbons resonating and the results were consistent with the assigned formulations [35]. The 1H NMR spectra of naphthylamide (NI)-boron dipyrromethene (BODIPY) dyads (4 and 5) and dendrimeric NI-BODIPY-cyclotriphosphazene triad systems (7 and 8) exhibited sets of signals for aromatic protons at around 8.6-6.6 ppm region (Fig. S5, S8, S10 and S13). The pyrrole ring -NCH protons for 7 and 8 appeared as sharp singlets at 6.6 ppm. The aliphatic – OCH2 protons of the compounds (4, 5, 7 and 8) showed triplet peaks, while -POCH2 protons of the 7 and 8 gave singlet peaks at 4.6 ppm. The - CH2N3 protons for 4 and 5 were observed at 3.7 ppm, whereas the -NCH2- protons for cyclotriphosphazene triads were seen at 4.5 ppm. The aliphatic -CH2 and -CH3 protons on the NI-BODIPY dyads were observed at around between 2.7-1.0 ppm as multiplet peaks for all compounds (4, 5, 7 and 8). All integrals confirmed proposed structures. The proton-decoupled

31P

NMR spectra of dendrimeric NI-BODIPY-

cyclotriphosphazene triads (7 and 8) showed an A3 spin system as expected, with a sharp single peak at  = 22.5 and 22.2 ppm, owing to the chemical environment equality of all the phosphorus nuclei (Fig. S12 and S15). In the 13C NMR spectra of the compounds (4, 5, 7 and 8), the aliphatic carbons were observed at about between 67-13 ppm, while aromatic carbons were observed between 165-111 ppm region (Fig. S6, S9, S11 and S14).

4.2. Photophysical Properties The electronic absorption profiles of NI-BODIPYs (4 and 5) and NI-BODIPYcyclotriphosphazene triads (7 and 8) were investigated in different solvents such as tetrahydrofuran (THF), dichloromethane (DCM), chloroform, acetone, acetonitrile, methanol, ethanol, dimethylsulfoxide (DMSO), DMSO:water (20:1;v:v), benzene, toluene, THF:water (20:1;v:v), acetonitrile:water (20:1;v:v), acetone:water (20:1;v:v). The absorption behaviors were observed to be not significantly affected by the solvent (Fig. 1, Fig. S16 and Fig. S20). NI-BODIPY-cyclotriphosphazene 7 and 8 exhibited absorption bands ~560 and ~627 nm respectively characteristic for the mono- and di-styryl BODIPY derivatives [36]. In addition,

the ground state absorption spectra of the compounds 4, 5, 7 and 8 were measured at different concentrations both in acetone and THF-water (20:1; v:v) (See Supporting Information). The studied concentration ranges were matched with Beer-Lambert law for both studied solvents. The molar absorption coefficient (ε) of triad systems (7 and 8) were found to be higher than parent NI-BODIPYs (4 and 5) whereas molar absorptivity of the molecules are solvent dependent and found to be are higher in THF:water (20:1;v:v) than acetone (Fig. S17, S18, S21, S22, S24-S27). In the absorption spectrum of compound 4, a trace signal in the range of 600650 nm was also detected which is pertinent with the presence of compound 5 as impurity. The fluorescence emission spectra of compounds 4, 5, 7 and 8 were also investigated in the above-mentioned solvents with an excitation wavelength of 530 and 610 nm at room temperature (Fig. 2, Fig. S19, Fig S23). The fluorescence emissions were observed to be higher for both triads (7 and 8) in acetone, acetonitrile, acetonitrile-water (20:1;v:v) whereas compound 7 was less emissive in methanol, ethanol, acetone:water (20:1;v:v), DMSO and DMSO:water (20:1; v:v) and compound 8 exhibited minimal fluorescence in toluene, benzene, DMSO and DMSO:water (20:1; v:v).

Fig. 3 exhibited excitation and emission spectra of NI derivative (2) and NI-BODIPYcyclotriphosphazenes (7 and 8). Excitation spectra displayed typical absorption bands of NI (~ 355 nm) [37] and mono- and distyryl- BODIPY sub-units (550-650 nm). The excitation profiles of NI moiety in all compounds (2, 4, 5, 7 and 8) (Fig. 3 and Fig. S28) preserved its uniformity. The characteristic S0-S1 transitions of NI-BODIPY (4 and 5) and NI-BODIPYcyclotriphosphazenes (7 and 8) were similar with the literature results and observed at 570 (compounds 4 and 7) and 638 nm (compounds 5 and 8) [36]. Moreover, NI units on mono- and di-styryl- NI-BODIPYs dyads (4 and 5) and NI-BODIPY-cyclotriphosphazene triads (7 and 8) were also excited at 345 nm and the emission spectra of these dyads and triads only introduced identical emission peaks with the ones, excited at BODIPY moieties which may indicate the excitation energy transfer between the NI and BODIPY sub units. Actually, the emission of the NI moiety was observed to be intersect with the BODIPY absorption bands for NI-BODIPY (4, 5) and NI-BODIPY-cyclotriphosphazene (7, 8). The excitation spectra of the compounds (7 and 8) in acetone provide additional information on NI unit provoked the emission of the BODIPY units (Fig. 3) and the excitations were found to be in well correspondence with the related absorptions. The fluorescence quantum yields of NI-BODIPYs (4, 5) and NI-BODIPYcyclotriphosphazene (7, 8) were calculated to be 0.61, 0.65, 0.73, 0.77, respectively (Table 1).

Also, time-correlated single photon counting (TCSPC) technique was used to determine the emission decay profiles of compounds (4, 5, 7 and 8) were measured at room temperature. All compounds featured a monoexponential decay with τ= 2.67, 3.94, 2.57 and 3.96 ns in acetone and τ= 3.48, 3.76, 3.47 and 3.83 ns in THF-water (20:1;v:v) respectively (Fig. S29, S30) (Table 1). 3D spectra of compounds 4, 5, 7 and 8 were measured in acetone to evaluate photophyisical features (Fig. 4, S31 and S32). 3D- fluorescence spectra of all compounds (4, 5, 7 and 8) displayed coherence with 3D-fluorescence emissions of related compound. The strongest transition for compound 7 was occurred via excitation at 370 and 556 nm where the strongest emission occurred ~569 nm whereas compound 8 gave fluorescence emission at 640 nm while excited both at 365 and 613 nm. The mono- and di-styryl NI-BODIPY systems (4 and 5) exhibit the same profile and gave emission at 569 and 636 nm respectively while exciting both sub units [λex= 370, 555 nm (4), 370, 612 nm (5)]. 4.3. Antimicrobial activity Caruso et al. showed that PAAs, a family of moderately basic polymers obtained by Michaeltype polyaddition of amines to bisacrylamides, improved the photoinduced bacteria killing efficacy of BODIPY moieties due to an increased interaction of the photosensitizers with the cell wall causing higher permeability. They concluded that this double action treatment might be successfully applied to defeat the bacterial resistance often encountered with many antibacterial drugs. In another study, BODIPY with a reactive end group were demonstrated at killing S. aureus by producing singlet oxygen. It was suggested that it might be easily modifiable for future antimicrobial surface development [19]. These findings were promising for the newly synthesized triads for antimicrobial applications. The antimicrobial susceptibility of the naphtalimide-BODIPY-cyclotriphosphazene triads (7 and 8) were investigated. The Kirby-Bauer disk diffusion method was used as antimicrobial susceptibility testing method. MHA plates inoculated with the tested Gram-positive Staphylococcus aureus and Gramnegative Escherichia coli bacteria at a concentration of 105 CFU/mL. The results showed that the tested molecules highly inhibited the growth of Gram-positive Staphylococcus aureus but not affected on gram-negative Escherichia coli. Inhibition zones were 16 ± 4 and 23 ± 5 mm for 7 and 8, respectively (Table 2). Many studies pointed out the potential roles of BODIPYs as an antimicrobial agent against both Gram-positive and Gram-negative bacteria [38, 39]. Conclusion

In summary, the series of naphtalimide-BODIPY dyads (4 and 5) naphtalimide-BODIPYcyclotriphosphazene triads (7 and 8) were prepared. The chemical structures of the dyad and triad systems were successfully characterized by NMR (31P, 1H and 13C) spectroscopies. Their photophysical properties including absorption, emission profiles, fluorescence quantum yield and fluorescence lifetime were investigated. Mono-styryl-NI-BODIPY-cyclotriphosphazene triad (7) exhibited intense absorption band about 520 and 560 nm for naphtalimide and BODIPY moieties. On the other hand, the same bands for di-styryl-NI-BODIPYcyclotriphosphazene triad (8) were observed around 580 and 630 nm due to the expanding conjugation of the structure. The molar absorption coefficient (ε) of triad systems were found to be higher than parent NI-BODIPY dyads. Although NI-BODIPYs and NI-BODIPYcyclotriphosphazene derivatives presented similar emission profile, fluorescence quantum yields of triads were determined higher than that of dyads which could be attributed to the increasing number of chromophore groups in a unit molecule. Also, the NI-BODIPYcyclotriphosphazene derivatives showed antimicrobial activity against Gram-positive Staphylococcus aureus bacteria. Triad systems could offer as a molecule model system for the design of new biological materials in the fields of biomedicine and environmental protection.

Acknowledgment This work was supported by the GTU-BAP project no: 2018-A-105-24.

Scheme 1. Synthesis of the Naphtalimide-BODIPY-Cyclotriphosphazene triads (7 and 8)

Fig. 1. Absorption responses of compounds (A) 7, (B) 8 in various solvents (1.0 µM)

Fig. 2. Fluorescence responses of compounds (A) 7, (B) 8 in various solvents (0.1 µM).

Fig. 3. Fluorescence excitation and emission spectra of compounds 2, 7 and 8 (0.1 μM) in acetone

Fig. 4. 3D fluorescence emission maps of compounds (A) 7 and (B) 8 in acetone (1.0 µM)

Table 1. Photophysical features of the compounds 4, 5, 7 and 8 Compound

Absorption

Emission

Wavelength

Wavelength

λab (nm) 522, 560

λem (nm) 568, 614

∆Stokes (nm)

aε,

cτ F

104 (M-1 cm-1)

(ns)

Acetone 8 11.83 THF-Water 524, 563 573, 618 10 13.57 (20:1) Acetone 578, 627 638, 700 11 9.78 5 THF-Water 582, 631 642, 706 11 11.23 (20:1) Acetone 521, 560 572, 616 12 64.23 7 THF-Water 524, 563 575, 622 12 71.03 (20:1) Acetone 578, 627 639, 698 12 63.14 8 THF-Water 582, 631 642, 700 11 66.71 (20:1) aMolar extinction coefficients, bFluorescence quantum yield, cFluorescence lifetime 4

b𝚽

𝐅

2.67 3.48

0.61

3.93 3.76

0.65

2.57 3.47

0.73

3.97 3.83

0.77

Table 2. Microbial growth inhibition zones diameters (mm) obtained in the presence of the DMSO stock solutions of the tested materials. DMSO Compound 7 (100µM) Compound 8 (100µM)

Staphylococcus aureus 16 ± 4 23 ± 5,5

Escherichia coli -

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Cyclotriphosphazene Cored Naphtalimide-BODIPY Dendrimeric Systems: Synthesis, Photophysical and Antimicrobial Properties

Elif ŞENKUYTUa, Ezel ÖZTÜRKa, Fatma AYDINOĞLUb, Esra TANIVERDİ EÇİKc, Elif OKUTANa*

a

Department of Chemistry, Faculty of Science, Gebze Technical University, Gebze, Kocaeli,

Turkey b

Department of Molecular Biology and Genetics, Faculty of Science, Gebze Technical

University, Gebze, Kocaeli, Turkey c Department of Chemistry,

Faculty of Science, Ataturk University, Yakutiye, Erzurum, Turkey

Cyclotriphosphazene Cored Naphtalimide-BODIPY Dendrimeric Systems: Synthesis, Photophysical and Antimicrobial Properties

Elif ŞENKUYTUa, Ezel ÖZTÜRKa, Fatma AYDINOĞLUb, Esra TANIVERDİ EÇİKc, Elif OKUTANa*

a

Department of Chemistry, Faculty of Science, Gebze Technical University, Gebze, Kocaeli,

Turkey b

Department of Molecular Biology and Genetics, Faculty of Science, Gebze Technical

University, Gebze, Kocaeli, Turkey c Department of Chemistry,

Faculty of Science, Ataturk University, Yakutiye, Erzurum, Turkey

Highlights 

Synthesis of new Naphtalimide-BODIPY-cyclotriphosphazene dendrimeric systems



Investigation of photophysical properties



The antimicrobial activity of dendrimeric systems were screened against Gram-positive and Gram-negative bacterial strains