Design, photochemistry and antibacterial evaluation of novel light-harvesting antenna

Article abstract of DOI:10.1080/00397911.2020.1788601

Novel light-harvesting compound 6, based on 1,8-naphthalimide donors and perylenediimide acceptor were synthesized. The light-harvesting compound 6 showed intensive absorption band in range between 390 and 560 nm, that is 50 nm wider in comparison with the absorption of the model perylene dye. The novel antenna 6 has a higher ability to collect photons from environment in comparison with the single perylene diimide dyes. The chosen fluorophore units are suitable donor–acceptor pair for light-harvesting materials which was in agreement with their good antibacterial activity.

Full text of DOI:10.1080/00397911.2020.1788601

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Design, photochemistry and antibacterial
evaluation of novel light-harvesting antenna
Alaa R. Sakr , Nikolai I. Georgiev & Vladimir B. Bojinov
To cite this article: Alaa R. Sakr , Nikolai I. Georgiev & Vladimir B. Bojinov (2020): Design,
photochemistry and antibacterial evaluation of novel light-harvesting antenna, Synthetic
Communications, DOI: 10.1080/00397911.2020.1788601
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https://doi.org/10.1080/00397911.2020.1788601
Design, photochemistry and antibacterial evaluation of
novel light-harvesting antenna
Alaa R. Sakra,b, Nikolai I. Georgieva, and Vladimir B. Bojinova
aDepartment of Organic Synthesis, University of Chemical Technology and Metallurgy, Sofia, Bulgaria;
bDepartment of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt
ABSTRACT
ARTICLE HISTORY
Received 6 April 2020
Novel light-harvesting compound 6, based on 1,8-naphthalimide
donors and perylenediimide acceptor were synthesized. The light-
harvesting compound 6 showed intensive absorption band in range
between 390 and 560 nm, that is 50 nm wider in comparison with
the absorption of the model perylene dye. The novel antenna 6 has
a higher ability to collect photons from environment in comparison
with the single perylene diimide dyes. The chosen fluorophore units
are suitable donor–acceptor pair for light-harvesting materials which
was in agreement with their good antibacterial activity.
KEYWORDS
Antibacterial activity;
fluorescence; fluorophore;
18-naphthalimide donors;
perylene-34910-tetracarbox-
ylic diimide
GRAPHICAL ABSTRACT
Introduction
Perylene diimides exhibit a unique combination of electrooptical properties. They are
[1–3]
highly stable and widely used for organic electronic devices such as solar cells,
[4–6]
[7,8]
field-effect transistors,
light-emitting diodes,
in liquid crystal displays,[9,10] as
[14,15]
chemosensing materials,[11–13] light-harvesting materials
and as dyes in photo-
dynamic therapy.[16] However, most of the synthesized dyes possess low solubility in
organic solvents; this is a serious drawback for their processing and material science
applications.[17,18] Usually, the solubility is improved with the long-tail or swallow-tail
conformation that is obtained by long alkyl substitutions in N-position of the dye.[19–21]
CONTACT Alaa R. Sakr
alaasakr81@yahoo.com
Department of Organic Synthesis, University of Chemical
Technology and Metallurgy, Sofia, Bulgaria.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

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A. R. SAKR ET AL.
Scheme 1. Light harvesting antenna 6.
Dendrimers are macromolecules exhibiting a three-dimensional structure that is
roughly spherical or globular. A characteristic of dendritic macromolecules is the pres-
ence of numerous peripheral chain ends that all surround a single core.[22,23] The usage
of perylene diimides as dendrimer core would increase their solubility in organic sol-
[24,25]
vents due to the dendritic swallow-tail conformation.
The polyamidoamine
(PAMAM) is a class of commercial dendrimers. Considerable interest in PAMAM den-
dritic macromolecules has arisen because of their novel structural properties and wide
range of potential applications.[26–30] Constructing a PAMAM dendrimer around a
luminescent group could profitably alter the luminescence signals in the macromolecu-
lar structure and amplify the signals for sensing purposes.[31–35]
Results and discussion
Considering the need for effectively using renewable energy sources, molecular systems
capable of light-harvesting and energy transfer are currently of great interest. Nature
has already evolved an effective pathway for harvesting sunlight in to useful chemical
energy. Studies on the natural photosynthetic systems revealed that the structure of the
photosynthetic unit is a central reaction center surrounded by light-harvesting com-
plexes. The remarkable character of the photosynthetic system is that the energy of any
photon absorbed by antenna complexes is transferred with greater than 90% efficiency.
Progress in the study of natural photosynthetic systems has provided the impetus to
[32,36]
design artificial light-harvesting assemblies based on a variety of architectures.
In
this work, we were focused on the preparation of novel light-harvesting compound 6,
based on 1,8-naphthalimide donors and perylenediimide acceptor (Scheme 1).
A requirement for efficient energy transfer is that there be a spectral overlap between
the emission of the peripheral donor dyes and the absorbance of the focal acceptor
chromophore. It is well known that absorption and fluorescence characteristics of the
1,8-naphthalimides depend on the nature of the substituent at C-4 position of the

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3
Figure 1. Normalized absorption of 8 and fluorescence of 5 in DMF solution.
Yield (88%)
Scheme 2. Synthesis of the starting 4-nitro-1,8-naphthalic anhydride 3.
1,8-naphthalimide ring.[37] 4-Alkylamino-1,8-naphthalimide derivatives are yellow-green
emitting fluorophores with maximal fluorescence at about kA¼430 ꢀ 440 nm, where the
absorbance of perylene diimide is appeared. Consistent with the requirement, perylene
dimides and 4-alkylamino-1,8-naphthalimides are suitable fluorescence donor–acceptor
pairs for light-harvesting systems (Fig. 1).
The novel light-harvesting antennae were prepared in three basic steps: synthesis of
4-nitro-1,8-naphthalic anhydride, synthesis of amino-functional yellow-green emitting
1,8-naphthalimide donors and coupling of the 1,8-naphthalimide donors to a focal pery-
lene diimide.
The starting 4-nitro-1,8-naphthalic anhydride 3 was prepared in two steps as
shown in Scheme 2. First, 4-nitro-acenaphtene 2 was obtained by nitration of ace-
naphtene 1 with 48% nitric acid. Then the intermediate compound 1 was converted
into the desire 4-nitro-1,8-naphthalic anhydride
sodium bichromate.
3
after oxidation with
The synthesis of amino-functional 1,8-naphthalimide donors 5 was performed follow-
ing Scheme 3. First, 4-nitro-N-(2,2,6,6-tetramethylpiperidin-4-yl)-1,8-naphthalimide 4

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A. R. SAKR ET AL.
Yield (83%)
Scheme 3. The synthesis of amino functional 1,8-naphthalimide donors 5.
Yield (86%)
Scheme 4. The synthesis of light harvesting antenna 6. The synthesis of perylene diimides 8 was
achieved as shown in Scheme 5. The reference compound 8 was synthesized as described before[41]
by refluxing perylene-3,4,9,10-tetracarboxy anhydride and n-butylamine in water/propanol. The pure
dye 8 was obtained after removing the unreacted anhydride under boiling the crude solid in 5%
aqueous sodium hydroxide. The structure and purity of the desired products were confirmed by con-
ventional techniques (elemental analysis data, UV/VIS, fluorescence, FT-IR and 1H NMR spectroscopy).
was obtained by reaction of 4-nitro-1,8-naphthalic anhydride 3 with 2,2,6,6-tetramethyl-
piperidin-4-ylamine in ethanol at boiling. The intermediate 4 was converted into the
desire flurophore 5 by reaction with ethylendiamine in DMF at room temperature
for 48 h.
The final light-harvesting antenna 6 was obtained by reaction of amino-functional
1,8-naphthalimide 5 with perylene-3,4,9,10-tetracarboxy anhydride 7, as shown in
Scheme 4. The process was performed in DMF media at boiling point. Synthesized
compounds were characterized and identified by their melting points, TLC (Rf values),
1
UV-VIS, FT-IR and H NMR spectroscopy.
The absorption spectra of light-harvesting antennae 6 as expected corresponded to
the sum of the absorption spectra of model peylene tetracarbxy diimide acceptor 8 and
1,8-naphthalimide donors 5 (Fig. 2). This indicates that there is no electronic communi-
cation between donor and acceptor units in antenna 6 through the ethylene spacer. The
light-harvesting compound 6 shows intensive absorption band in range between 390

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5
Figure 2. Normalized absorption spectra of 5, 6 and 8 in DMF solution.
Scheme 5. The synthesis of the reference compound 8.
Figure 3. Normalized to the optical density fluorescence spectra of 5, 6 in DMF solution.
and 560 nm, that is 50 nm wider in comparison with the absorption of the model pery-
lene dye 8. This phenomenon clearly shows that the novel antenna 6 has a higher ability
to collect photons from environment in comparison with the single perylene diimide
dyes. Also, the absorption band of antenna 6 is in the region, where the solar radiation
spectrum shows higher intensity. This, together with the fact that the perylene diimides
are commonly used in dye solar cells to determinate the novel antenna 6 as a suitable
material for photosensitizer in photovoltaic devices (Scheme 5).

6
A. R. SAKR ET AL.
Table 1. Mean zone of inhibition in mm produced on a range of pathogenic microorganisms results
are depicted in the following table.
Sample code
Control
Mean IZ
Gentamycin
3
4
5
6
Tested microorganisms
Mean IZ
Mean IZ
Mean IZ
Mean IZ
SD
Gram-positive bacteria
Bacillus subtilis: RCMB 015 (1) NRRL B-543
Gram-negatvie bacteria
Escherichia coli: (RCMB 010052) ATCC 25955
Pseudomonas aeruginosa
ꢁ
15
10
12
12
12
NA
26.02
0.03
Gentamycin
15
18
12
NA
29.90
21.01
0.01
0.04
ꢁ
ꢁ
ꢁ
NA
NA
The test was done using the diffusion agar technique, well diameter: 6.0 mm (100 ml was tested), RCMB: Regional
Center for Mycology and Biotechnology.
Positive control for bacteria Gentamycin 4 mg/ml.
ꢁ
NA: No activity. The sample was tested at 5 mg/ml concentration.
Figure 3 presents normalized to the optical density fluorescence spectra of the single
donor compound 5 and antenna 6, excited at 420 nm, where is appeared only the
absorption of the donor 1,8-naphthalimides. As can be seen from the figure, no emis-
sion of donor 1,8-naphthalimide has been recorded in the fluorescence spectra of
antenna 6. This result demonstrates that the entire energy absorbed by the donor 1,8-
naphthalimides is transferred as a fluorescence emission to the acceptor perylene.
By applying the Eq. (1)[38], where FDA is normalized to the optical density fluores-
cence intensity of the donor in the presence of acceptor (light-harvesting antenna 6)
and FD is normalized to the optical density fluorescence intensity of the donor without
acceptor (model compound 5), the efficiency of the energy transfer ET in the light-har-
vesting antenna was calculated to 98%.
E ¼ 1 ꢀ FAD=FD
(1)
The above results suggest that the chosen fluorophore units are suitable donor–accep-
tor pair for light-harvesting materials.
Antibacterial evaluation of the synthesized dyes
Some of the synthesized compounds were tested for antimicrobial activity using the
agar diffusion method[39,40] against representatives of Gram-positive bacteria (Bacillus
subtilis) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa)
(Table 1).
Compounds 3, 4, 5 and 6 have excellent results against Gram-negative bacteria (E.
coli) and the most effective compound against Gram-negative bacteria (E. coli and P.
aeruginosa) is 5 and inhibition zone for compound 5 is 15 and 18 mm, respectively, and
the best result against Gram-positive bacteria for compound 3 while inhibition zone is
15 mm, in general compounds were tested have a good antibacterial activity as com-
pared with standard compounds (Gentamycin).
Experimental
Melting points were measured using an Electrothermal IA 9100 apparatus with open
capillary tube and are uncorrected. The IR spectra (KBr disc) were recorded on a

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7
PyeUnicam Sp-3-300 or a Shimadzu FT-IR 8101 PC infrared spectrophotometer. The
1H NMR and 13C NMR spectra were measured on a JEOL-JNM-LA 400 MHz
(100 MHz) spectrometer using DMSO-d6 as a solvent. All chemical shifts were expressed
on the d (ppm) scale using TMS as an internal standard reference. The coupling con-
stant (J) values are given in Hz.
General procedure for the synthesis of light-harvesting antenna (6)
A suspension of 4-(2-aminoethyl)amino-N-(2,2,6,6-tetramethylpiperidin-4-yl)-1,8-naph-
thalimide 5 (0.5 g, 1.2 mmol) and perylene-3,4,9,10-tetracarboxylic acid dianhydride (7)
(0.5 g, 0.6 mmol) in 20 ml of DMF was refluxed with stirring for 24 h. The crude prod-
uct was filtered off, washed with methanol to clear filtrate and treated with 25 ml of 5%
aqueous sodium carbonate. Then the solid phase was filtered off, washed water and
dried to give 0.59 g (86%) of pure light harvesting antenna 6, m.p.>250 ꢂC. IR (KBr)
cmꢀ1: 3397 (ꢀNH); 2958 (ꢀCH); 1692 (ꢀasN–C ¼ O); 1646 (ꢀsN–C ¼ O). 1H NMR
(CDCl3, 250.13 MHz) ppm: 9.09 (m, 18 H, Ar-H); 8,14 (m, 2H, 2 ꢃ naphthalimide H-
3); 6.53 (m, 2H, 2 ꢃ ArNH); 6.30 (m, 2H, 2ꢃ (CO)2NCH); 5.23 (m, 4H, 2 ꢃ
(CO)2NCH2); 5.01 (m, 2H, 2 ꢃ NH-piperidine); 4.52 (m, 4H, 2ꢃ CH2); 3.55 (t, 4H,
CH2-piperidine); 2.34 (d, 4H, CH2-piperidine); 2.09 (s, 12H, 4 ꢃ CCH3); 1.91 (s, 12H, 4
ꢃ CCH3). Anal. Calcd for C70H64N8O8 (1145.31): C, 73.34%; H, 5.58%; N, 9.77%,
Found: C, 73.41%; H, 5.63%; N, 9.78%.
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