Design and synthesis of light-harvesting rotor based on 1,8-naphthalimide units

Article abstract of DOI:10.1016/j.jphotochem.2020.112733

A novel pH and viscosity fluorescence sensing multicomponent molecular device based on 1,8-naphthalimide fluorophores is synthesized and investigated. The system is designed as a light-harvesting antenna where energy supplier, molecular rotor and molecular “on-off” switcher are integrated. The peripheral 1,8-naphthalimide energy suppliers transfer rapidly the trapped energy to the core molecular rotor through high efficient FRET (99 %). The 4-piperazinyl-1,8-naphthalimide core excitation results in a TICT driven molecular motion. Due to the non-emissive de-excitation nature of the TICT core fluorophore, system shows low yellow-green fluorescence that is a “power-on”/“rotor-on” state. The protonation of the methylpiperazine amine destabilized TICT process thus indicating a “power-on”/“rotor-off” system state.

Full text of DOI:10.1016/j.jphotochem.2020.112733

Journal Pre-proof
Design and synthesis of light-harvesting rotor based on
1,8-naphthalimide units
Nikolai I. Georgiev (Methodology) (Investigation) (Writing - original
draft), Nevena V. Marinova (Investigation) (Visualization), Vladimir
B. Bojinov (Supervision) (Conceptualization) (Writing - review and
editing)
PII:
S1010-6030(20)30532-3
DOI:
https://doi.org/10.1016/j.jphotochem.2020.112733
JPC 112733
Reference:
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Journal of Photochemistry & Photobiology, A: Chemistry
Received Date:
Revised Date:
Accepted Date:
15 April 2020
25 June 2020
26 June 2020
Please cite this article as: Georgiev NI, Marinova NV, Bojinov VB, Design and synthesis of
light-harvesting rotor based on 1,8-naphthalimide units, Journal of Photochemistry and amp;
Photobiology, A: Chemistry (2020), doi: https://doi.org/10.1016/j.jphotochem.2020.112733
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Design and synthesis of light-harvesting
rotor based on 1,8-naphthalimide units
Nikolai I. Georgiev, Nevena V. Marinova, Vladimir B. Bojinov*
Department of Organic Synthesis, University of Chemical Technology and Metallurgy, 8 Kliment
Ohridsky Str., 1756 Sofia, Bulgaria
* Corresponding author. Tel.: (+ 359 2) 8163169
E-mail address: vlbojin@uctm.edu (V.B. Bojinov)
GRAPHICAL ABSTRACT
HIGHLIGHTS



Multicomponent molecular device based on 1,8-naphthalimide fluorophores is synthesized.
Energy supplier, molecular rotor and switch are integrated in light-harvesting antenna.
The system shows high efficient FRET (99%).



Fluorescence changes of the antenna are caused by a TICT driven molecular motion.
Preventing the TICT motion in viscous or acid media increases the fluorescence output.
A B S T R A C T
A novel pH and viscosity fluorescence sensing multicomponent molecular device based on
1,8-naphthalimide fluorophores is synthesized and investigated. The system is designed as a
light-harvesting antenna where energy supplier, molecular rotor and molecular “on-off”
switcher are integrated. The peripheral 1,8-naphthalimide energy suppliers transfer rapidly the
trapped energy to the core molecular rotor through high efficient FRET (99%). The 4-
piperazinyl-1,8-naphthalimide core excitation results in a TICT driven molecular motion. Due
to the non-emissive de-excitation nature of the TICT core fluorophore, system shows low
yellow-green fluorescence that is a “power-on”/“rotor-on” state. The protonation of the
methylpiperazine amine destabilized TICT process thus indicating a “power-on”/“rotor-off”
system state.
Keywords: 1,8-Naphthalimide; Light-harvesting rotor; Energy transfer; Twisted internal
charge transfer (TICT); Fluorescent pH sensor; Viscosity sensing.
1.
Introduction
The rapid grow of nanotechnology pushes the science towards development of new
concepts and research fields. In this regard the construction of different devices at molecular
level became one of the most inspiring ideas in the scientific community [1-8]. In the past it
was extended form a fiction and illusion to give molecular architectures with practical
applications in object coding [9], sensing systems [10-15], data storage [16,17], drug delivery
[18,19] and drug activation [20,21]. Recently, the field of molecular devices has evaluated
from intramolecular motion [22-24] to nano-scale motion in artificial muscles [25-27], from
molecular switches [28,29] to a more complicated logic gates [30-32] and even logic circuits
[33,34] which are able to perform arithmetic function [35-37] and simple games [38].
Notably, examples of nano cars [39], molecular cursor caliper [40], molecular timers [41,42]

and molecular cryptography [43,44] were also reported. However, the orthogonal integration
of the different individually working molecular architectures in to a one global device is a
great challenge, which will attract the scientists in the next decades.
In this work we pay attention on the design and synthesis of a multicomponent
molecular device comprising a light-harvesting system, molecular rotor and molecular
switcher which are logically bonded to working cooperatively as a whole. The light-
harvesting systems represent energy suppliers at a molecular level that are based on the
natural photosynthetic units [45-47]. Similarly to the natural light-harvesting complexes, the
artificial light-harvesting architectures are able to absorb and transport light energy over a
distance with minimal losses using fluorescence resonance energy transfer (FRET) [48]. The
energy and energy supply are essential in the design of every molecular device. That is why
we focused the present work on the construction around a light-harvesting system using the
light as a most accessible energy source at molecular level. The most of reported molecular
rotors and machines were based on photo isomerization [49-51]. However, from a practical
point of view, herein we chose the TICT (twisted internal charge transfer) driven motion as a
molecular rotor. The relaxation from TICT excited state is non-radiative or shows lower
energy (high wavelength) than normal fluorescence emission and found useful application in
different fluorescent probes, which are especially valuable for imaging of microenvironmental
viscosity in biological objects [52-55]. Furthermore, the difference in the de-excitation
between TICT and normal state could be used as “power-on”/“power-off” indicator at
molecular level giving us information about presence or lack of motion in the TICT-rotor. The
molecular architecture that is the subject of this study is presented in Scheme 1. It was based
on 1,8-naphthalimide fluorogenic compounds, which have application in a wide areas because
of their unique properties such as higher chemical and photo stability, higher quantum yields
of fluorescence and relatively long Stoke shifts [56-58].
Insert here Scheme 1
2.
Experimental
2.1. Materials and methods
The starting 1,8-naphthalimide labelled benzylether 3 and 1,8-naphthalimide 6 were
synthesized as we reported before [59,60]. The used solvents (Aldrich, Fisher Chemical) were
pure or of spectroscopy grade. The synthetic process was controlled by thin-layer

chromatography (TLC). TLC analysis was performed on silica gel, ALUGRAM®SIL
G/UV254, 40×80 mm, 0.2 mm silica gel 60 with fluorescent indicator. FT-IR spectra were
obtained on a Varian Scimitar 1000 spectrometer. The 1H and 13C NMR spectra (chemical
shifts are given as  in ppm) were recorded on a Bruker AV-600 spectrometer operating at
600 MHz and 151 MHz, respectively. Electrospray ionization mass spectra (ESI-MS) were
obtained on a BRUKER micrOTOF-Q system. The UV-VIS absorption spectra were recorded
on a spectrophotometer Hewlett Packard 8452A. The fluorescence measurements were
performed on a Scinco FS-2 fluorimeter. The quantum yields of fluorescence (ΦF) were
calculated using 9,10-diphenylanthracene as a standard (ΦF = 0.95 in ethanol) [61]. The UV-
Vis and steady-state fluorescence investigations were performed at room temperature (20°C)
in a 1×1 cm quartz cuvettes. A very small volume of hydrochloric acid and sodium hydroxide
was used to adjust the pH which was monitored by HANNA®instruments HI-2211 Bench
Top pH meter. The viscosity measurements were performed in binary mixtures ethylene
glycol/glycerol using Ubbelohde capillary viscometer.
2.2. Synthesis of light-harvesting system 7
To a solution of 0.12 g 1,8-naphthalimide 6 (0.0003 mol) and 0.017 g KOH (0.0003
mol) in 1 mL of DMF, a solution of 0.21 g 1,8-naphthalimide labelled benzylether 3 (0.0003
mol) in 1 ml of DMF was added. The mixture was stirred 48 h at room temperature (20°C)
and then it was poured into 4 mL of water. The precipitated solid was filtered off and dried.
The desired light harvesting system 7 was obtained as yellow crystals (m.p. 167-170°C) using
silica gel column chromatography (Rf = 0.71 in chloroform:methanol = 9:1). Yield 0.11 g
(36%). FT-IR (KBr) cm-1: 2815 (νCH); 1696 (νasN-C=O); 1680 (νasN-C=O); 1654 (νsN-
C=O); 1648 (νsN-C=O). 1H NMR (CHCl3-d, 600 MHz) δ ppm: 8.59 (d, 2H, J = 7.2 Hz, 2 ×
donor 1,8-naphthalimide H-5); 8.56 (d, 2H, J = 8.5 Hz, 2 × donor 1,8-naphthalimide H-7);
8.55 (d, 1H, J = 7.3 Hz, acceptor 1,8-naphthalimide H-5); 8.48 (d, 1H, J = 8.2 Hz, acceptor
1,8-naphthalimide H-2); 8.47 (d, 2H, J = 8.2 Hz, 2 × donor 1,8-naphthalimide H-2); 8.39 (d,
1H, J = 8.5 Hz, acceptor 1,8-naphthalimide H-7); 7.72 (t, 2H, J = 7.8 Hz, 2 × donor 1,8-
naphthalimide H-6); 7.65 (t, 1H, J = 7.9 Hz, acceptor 1,8-naphthalimide H-6); 7.18 (d, 1H, J
= 8.2 Hz, acceptor 1,8-naphthalimide H-3); 7.16 (d, 2H, J = 8.8 Hz, Phenyl H-2, H-6); 7.13
(d, 2H, J = 2.0 Hz, Benzyl H-2, H-6); 7.05 (d, 2H, J = 8.2 Hz, 2 x donor 1,8-naphthalimide H-
3); 7.00 (d, 2H, J = 8.8 Hz, Phenyl H-3, H-5); 6.87 (t, 1H, J = 1.9 Hz, Benzyl H-4); 5.11 (s,
2H, Benzyl CH2); 4.10 (t, 4H, J = 7.6 Hz, 2 × CONCH2CH2); 3.27 (br.s, 4H, 2 × Piperazine

CH2); 2.72 (br.s, 4H, 2 × Piperazine CH2); 2.39 (s, 3H, Piperazine NCH3); 1.63 (m, 4H, 2 ×
CONCH2CH2); 1.37 (m, 4H, 2 × CONCH2CH2CH2); 0.90 (t, 6H, J = 7.4 Hz, 2 × CH2CH3).
13C NMR (CDCl3-d, 151 MHz) ppm: 164.86, 163.32, 160.87, 158.61, 144.02, 136.88, 132.63,
129.29, 129.02, 127.27, 127.36, 125.08, 122.75, 121.03, 118.57, 70.41, 60.9, 56.45, 50.92,
47.35, 40.11, 20.03, 14.05. Positive-ion ESI-MS at m/z: 1013,1136 [M+H]+. Elemental
analysis: calculated for C62H53N5O9 (MW 1012.11) C 73.58; H 5.28; N 6.92%; found C
73.92; H 5.40; N 7.15%.
3.
Results and discussion
3.1. Design and synthesis
The main task in this work was to construct a molecular device around light-
harvesting system which is able to transport energy with high efficiency using FRET. FRET is
a distant depended process which generally requires a higher overlap between the normalized
donor fluorescent and acceptor absorption spectra. The 4-oxy-1,8-naphthalimides have
fluorescence which completely overlaps the absorption spectra of 4-amino-1,8-naphthalimides
making the both 1,8-naphthalimide derivatives excellent candidates for a FRET donor-
acceptor pair with practical application [59,60,62-64]. This was the reason to base our light-
harvesting architecture on 4-phenoxy-1,8-naphthalimide donor fluorophores and 4-amino-1,8-
naphthalimide chromophoric acceptor. The donor and acceptor parts were covalently attached
each to another using benzyl ether unit. The benzyl ether unit is a basic monomer for
synthesis of poly(benzyl ether) dendrimers, which are the most common platform for light-
harvesting materials [65-67]. Furthermore, in order to obtain TICT driven rotor in the energy
acceptor, 1,8-naphthalimide was bound to dialkylamine at position C-4. It is well known that
1,8-naphthalimides containing at C-4 position dialkylamines such as N-methylbuthylamine,
morpholine, piperidine and piperazine show TICT after excitation, which is why they could
find application as fluorescent probes for viscosity [68-71]. Particularly, in this work we
chose 4-piperazinyl-1,8-naphthaimide as TICT rotor due to the possibility to control the TICT
efficiency in the molecule. Furthermore, the protonation of N-methyl piperazine amine
destabilized the TICT excited state thus preventing rotation. As a result the fluorophore
emission significantly increased and the observed phenomenon was widely used in the design
of pH-probes [71-73].

The light-harvesting antenna 7 under study was prepared as shown on Scheme 2. First,
the donor 1,8-naphthaimide functional benzyl ether 3 was obtained as we reported before after
reaction of 4-nitro-N-buthyl-1,8-naphthaimide 1 and 3,5-dihydroxybenzyl alcohol and
following replacement of hydroxyl group in 2 with bromine after treatment with Ph3P and
CBr4 [59]. Further, the yellow-green emitting acceptor 1,8-naphthalimide 6 was prepared
according previously reported synthetic procedure in which 4-nitro-1,8-naphthalic anhydride
4 was coupled with 4-aminophenol and nucleophilicaly substituted at C-4 position with N-
methylpiperazine [60]. The final light-harvesting antenna was obtained after interaction of
intermediates 3 and 6 using the classical Williamson’s ether synthesis in the presence of
potassium hydroxide.
Insert here Scheme 2
The synthesized light-harvesting rotor 7 was characterized and identified by TLC,
elemental analysis data, UV-VIS, fluorescence, FT-IR, 1H NMR, 13C NMR and mass
spectroscopy. For instance, in the 1H NMR spectrum a resonance at 7.72 ppm (Figure 1) was
observed, which is characteristic for the proton in position C-3 of the periphery blue emitting
1,8-naphthalimide ring, substituted in position C-4 with an electron-donating oxy group. This
resonance is different from the corresponding resonance for the core “yellow-green” 1,8-
naphthalimide moiety containing piperazine at C-4 position, which appears at 7.65 ppm.
Furthermore, these resonances were unmixed with other signals and their ratio 2:1 (signal at
7.72 ppm/ signal at 7.65 ppm) clearly illustrated that two energy donating 4-oxy-1,8-
naphthalimides were bonded to one 4-piperazinyl-1,8-naphthalimide energy acceptor unit.
Insert here Figure 1-R1
3.2. Photophysical investigations
The main photophysical properties of the synthesized light-harvesting system 7 were
investigated in chloroform, acetonitrile, ethanol and DMF solutions. For better understanding
of the interaction between energy donating 4-phenoxy-1,8-naphthalimide units and 4-
piperazinyl-1,8-naphthalimide acceptor in 7, the intermediates 3 and 6 were also added in the
present study as referent compounds. The results obtained are summarized in Table 1. All
data in Table 1 are in consistency with the ICT nature of the 1,8-naphthalimide
chromophores. The 1,8-naphthalimides are typical push-pull systems in which light

absorption generates charge transfer from the electron donating group in C-4 position to the
electron accepting imide fragment [74,75]. The intermediate 3 containing 4-phenoxy-1,8-
naphthalimides is colourless and shows absorption maximum at 360 nm, while compound 6
which contains a high electron-donating amine in C-4 position is yellow-green and shows
maximal absorption at 400 nm due to the increased ICT efficiency.
Insert here Table 1
As can be seen from the data in Table 1 the absorption properties of the individual
energy donating and energy accepting 1,8-naphthalimide fragments 3 and 6 remain practically
unchanged after their coupling in a light-harvesting system 7. As a result the observed
absorption spectrum of a novel compound 7 represents a sum of the absorption spectra of both
referent intermediates 3 and 6 (Figure 2). It should be pointed out that in the absorption
spectrum of 7, the peripheral units showed about 3-times higher absorption at 360 nm in
comparison with the core absorption at 400 nm. This clearly illustrates the higher ability of
light-harvesting system 7 to capture photons through its periphery instead by direct core
excitation.
Insert here Figure 2-R1
The peripheral 1,8-naphthalimide units in the intermediate 3 showed a bright blue
fluorescence with maximum at 419 nm in chloroform solution (Figure 3). Due to the high
efficient energy transfer in light-harvesting system 7 this emission dramatically decreased
after coupling of 3 with the core energy accepting compound 6. The energy transfer efficiency
(ET) in antenna 7 was calculated to be 99.1% using Eq. (1) [76], where FD is the normalized
to the optical density (at 360 nm) fluorescence intensity of intermediate 3 and FDA is the
normalized to the optical density (at 360 nm) fluorescence intensity of the donor 1,8-
naphthalimides in antenna 7.
ET = 1 – FDA / FD
(1)
Insert here Figure 3-R1
Furthermore, it was found that after peripheral excitation at 360 nm antenna 7 has a
very similar photophysical behaviour such as individual core compound 6 excited at 400 nm.
Obviously, the captured energy is rapidly transferred from the peripheral 4-oxy-1,8-
naphthalimide units to the focal 4-piperazinyl-1,8-naphthalimide. Thus light-harvesting

system 7 showed predominated fluorescent properties of the energy accepting focal
fluorophore, which conformed the above suggested high efficient energy transfer. The novel
antenna 7 has in chloroform a low yellow-green fluorescent emission with maximum at 500
nm that is red shifted at about 520 nm in more polar solvents such as acetonitrile, ethanol and
DMF due to the ICT nature of the 1,8-naphthalimide. The quantum yield of fluorescence of
antenna 7 was calculated according Eq. (2) using 9,10-diphenylanthracene as a standard with
a well-known quantum yield (Φref = 0.95 in ethanol) [61]. The used symbols Aref, Sref, nref and
Asample, Ssample, nsample respectively represent the absorbance at the excitation wavelength, the
integrated fluorescence band area and the solvent refractive index of the standard and the
sample.




2





S
n
A

sample 
sample 
ref
ФF Ф
(2)








ref 

nr2ef




Sref
A
sample 



The so calculated quantum yields of fluorescence of 7 were strongly depended on the
solvent nature and rapidly decreased from ΦF = 0.16 in chloroform to ΦF = 0.02-0.01 in more
polar solvents such as ethanol and DMF. The same behaviour was observed before for
individual core compound 6 in which the quantum yield of fluorescence decreased from ΦF =
0.19 in chloroform to ΦF = 0.01 in methanol and DMF [60]. This phenomenon was attributed
to the existence of TICT process in the excited state of 4-piperazinyl-1,8-naphthalimides. It
should be pointed out that this effect could be result from a possible photoinduced electron
transfer (PET) from tertiary piperazine amine to the excited fluorophore, however recent
works in this area reported that the main reason for the quenching process in 4-piperazinyl-
1,8-naphthalimides is TICT [70-73]. In order to confirm the existence of TICT process in 7 it
fluorescence properties were investigated in solvents with different viscosity. For this purpose
the fluorescence spectra of 7 were measured in glycol, glycerol and glycol/glycerol mixtures
(Figure 4). The results observed logically were in line with the supposed TICT in core 1,8-
naphthalimide of antenna 7. The higher viscosity seriously restricted the intramolecular bond
rotation thus preventing the TICT process. As a result of that the yellow-green emission of
antenna 7 was about 6-fold higher in glycerol than in the less viscous glycol solution. Also,
the observed relationship in a double logarithmic scale between fluorescent intensity at 526
nm of 7 and solvent viscosity showed a good linearity (R2 = 0.9934) which is a characteristic
of the TICT rotors [53,77]. The observed results clearly illustrated the TICT nature of the

fluorescence quenching process in antenna 7 and showed its potential as a promising
fluorescent probe for viscosity.
Insert here Figure 4-R1
It should be pointed out that the examined antenna 7 loses its viscosity fluorescence
sensing properties in acid media. As can be seen from Figure 5, in glycol and glycerol
solutions buffered with 10 µM acetate buffer (pH 4.5) antenna 7 showed approximately the
same fluorescence spectrum with well pronounced core fluorescence, which was more than
expectable.
Insert here Figure 5-R1
The 4-piperazinyl-1,8-naphthalimides are widely used as pH fluorescent probes and
switches. After protonation of methyl piperazine amine the formed positive charge
destabilized the non-radiative TICT process and bright yellow-green fluorescence appeared.
This was the reason to investigate the “switch-on” and “switch-off” ability of the TICT
process in antenna 7 as a function of pH. For this purpose, the fluorescence and absorption
spectra of 7 were measured in water/DMF (v/v, 1:1) solution at different pHs. As we
expected, the absorption spectra remained unchanged over a wide pH range (Figure 6), while
the fluorescence of the core fluorophore at 526 nm significantly increased (about 7-fold) after
transition from alkaline to acid media due to the hindered TICT process (Figure 7). The pH-
switching mechanism was observed in a pH window 6-9 and the pKa = 7.03±0.11 of the
studied process was calculated according to Hendersen-Hasselbalch Eq. (3). This value is
very similar to the previously reported compounds with a similar nature and it easy could be
attributed to the protonation of methylpiperazine amine [60].
Insert here Figure 6-R1
Insert here Figure 7-R1
log I
 I / I  I
F  
  pH  pK

F min 
(3)
F max
F
a


Finally, all the results obtained could be summarized according to Scheme 3. The
novel antenna 7 is a multicomponent molecular device in which energy supplier, molecular
rotor and molecular switcher with “on-off” indicator are integrated. The both peripheral 1,8-
naphthalimides in the presented molecular architecture are energy supplier. Due to the higher
number of light absorbing units in its periphery (absorbing light at 360 nm) the molecular

system 7 has a better chance to capture photons and, as a consequence, to transfers rapidly the
trapped energy to the core molecular rotor through high efficient FRET. The 4-piperazinyl-
1,8-naphthalimide core excitation results in a TICT driven molecular motion. Due to the non-
emissive de-excitation nature of the TICT core fluorophore, system 7 shows low yellow-green
fluorescence that is an indication of a “power-on”/“rotor-on” state. The methylpiperazine
amine is a proton driven molecular “on-off” switcher which protonation destabilized TICT
process and “turns off” the molecular motion in antenna 7. The lack of TICT leads to a bright
yellow-green fluorescence de-excitation of core fluorophore in 7, as the observed emission is
an indication of a “power-on”/“rotor-off” system state.
Insert here Scheme 3-R1
The herein presented results could be contributed to the development of more
complicated molecular devices with practical application as pH-chemosensing and viscosity-
sensing materials.
4.
Conclusions
A novel light-harvesting antenna based on 1,8-naphthalimide units was synthesized
and photophysically investigated. 4-Phenyloxy-1,8-naphthalimide energy donating
fluorophores and 4-piperazinyl-1,8-naphthalimide acceptor dye were used as a donor-acceptor
pair in the system. High efficient energy transfer (99.1%) was obtained in the light-harvesting
system due to the higher overlap between the donor fluorescence and the acceptor absorption
spectra. Furthermore, the focal energy accepting 4-piperazinyl-1,8-naphthalimide, known for
its environmental sensitive fluorescence properties, was introduced as a TICT molecular rotor.
The novel antenna showed higher fluorescence output in more viscous or acid media due to
the prevented TICT motion in the excited state. In summary of the results obtained, the novel
system was implemented as a light-harvesting rotor with pH “off-on” rotating switcher and
power indicator at a molecular level. The presented here light-harvesting system demonstrates
high potential as a multicomponent molecular device with practical application as a pH and
viscosity sensing material.
CRediT author statement
Nikolai I. Georgiev: Methodology, Investigation, Writing- Original draft preparation.
Nevena V. Marinova: Investigation, Visualization.

Vladimir B. Bojinov: Supervision, Conceptualization, Writing- Reviewing and Editing.
Acknowledgements
This work was supported by National Science Fund of Bulgaria (project No KP-06-
H39/3). Authors also acknowledge the Science foundation of University of Chemical
Technology and Metallurgy (Sofia, Bulgaria).

References
[1]
[2]
W. Browne, B. Feringa, Making molecular machines work, Nat. Nanotechnol. 1
(2006) 25-35. https://doi.org/10.1038/nnano.2006.45
P. Martinez-Bulit, A. Stirk, S. Loeb, Rotors, motors, and machines inside metal-
organic frameworks, Trends Chem. 1 (2019) 588-600.
https://doi.org/10.1016/j.trechm.2019.05.005
[3]
C-Y. Yao, S. Uchiyama, A. de Silva, 2019. A personal journey across fluorescent
sensing and logic associated with polymers of various kinds. Polymers. 11, 1351.
https://doi.org/10.3390/polym11081351
[4]
[5]
[6]
P. Ceroni, Design of phosphorescent organic molecules: Old concepts under a new
light, Chem 1 (2016) 524-526. https://doi.org/10.1016/j.chempr.2016.09.011
A. de Silva, Molecular logic-based computation, Royal Society of Chemistry,
Cambridge, 2013. https://doi.org/10.1039/9781849733021
J. Andréasson, U. Pischel, Molecules for security measures: from keypad locks to
advanced communication protocols, Chem. Soc. Rev. 47 (2018) 2266-2279.
https://doi.org/10.1039/C7CS00287D
[7]
[8]
[9]
A. Credi, A molecular cable car for transmembrane ion transport, Angew. Chem. Int.
Ed. 58 (2019) 4108-4110. https://doi.org/10.1002/anie.201814333
P. Remon, U. Pischel, Chemical communication between molecules, ChemPhysChem
18 (2017) 1667-1677. https://doi.org/10.1002/cphc.201700387
J. Ling, G. Naren, J. Kelly, T. Moody, A.P. de Silva, Building pH sensors into paper-
based small-molecular logic systems for very simple detection of edges of objects, J.
Am. Chem. Soc. 137 (2015) 3763-3766. https://doi.org/10.1021/jacs.5b00665
[10] Q. Ruan, L. Mu, X. Zeng, J-L. Zhao, L. Zeng, Z-M. Chen, C. Yang, G. Wei, C.
Redshaw, A three-dimensional (time, wavelength and intensity) functioning
fluorescent probe for the selective recognition/discrimination of Cu2+, Hg2+, Fe3+ and
F- ions, Dalton Trans. 47 (2018) 3674-3678. https://doi.org/10.1039/C7DT04785A
[11] R. Shen, Y. Qian, A mitochondria-oriented fluorescent probe for ultrafast and
ratiometric detection of HSO3 - based on naphthalimide-hemicyanine, New J. Chem.
43 (2019) 7606-7612. https://doi.org/10.1039/C9NJ01467E
[12] Y. Wen, F. Huo, C. Yin, Organelle targetable fluorescent probes for hydrogen
peroxide, Chin. Chem. Lett. 30 (2019) 1834-1842.
https://doi.org/10.1016/j.cclet.2019.07.006

[13] L. Zhang, X. Liu, K. Gillis, T. Glass, A high-affinity fluorescent catecholamine
sensor: Application to monitoring norepinephrine exocytosis, Angew. Chem. Int. Ed.
58 (2019) 7611-7614. https://doi.org/10.1002/anie.201810919
[14] M. Xu, S. Kelley, T. Glass, A multi-component sensor system for detection of
amphiphilic compounds, Angew. Chem. Int. Ed. 130 (2018) 12741-12744.
https://doi.org/10.1002/anie.201807221
[15] Y. Wen, W. Zhang, T. Liu, F. Huo, C. Yin, Pinpoint diagnostic kit for heat stroke by
monitoring lysosomal pH, Anal. Chem. 89 (2017) 11869-11874.
https://doi.org/10.1021/acs.analchem.7b03612
[16] Y. Hou, J. Du, J. Hou, P. Shi, K. Wang, S. Zhang, T. Han, Z. Li, Rewritable optical
data storage based on mechanochromic fluorescence materials with aggregation-
induced emission, Dyes Pigm. 160 (2019) 830-838.
https://doi.org/10.1016/j.dyepig.2018.09.023
[17] B. Cafferty, A. Ten, M. Fink, S. Morey, D. Preston, M. Mrksich, G. Whitesides,
Storage of information using small organic molecules, ACS Cent. Sci. 5 (2019) 911-
916. https://doi.org/10.1021/acscentsci.9b00210
[18] E. Ruskowitz, M. Comerford, B. Badeau, C. DeFores, Logical stimuli-triggered
delivery of small molecules from hydrogel biomaterials, Biomater. Sci. 7 (2019) 542-
546. https://doi.org/10.1039/C8BM01304G
[19] M. Romero, P. Mateus, B. Matos, Á. Acuña, L. García-Río, J. Arteaga, U. Pischel, N.
Basílio, Binding of flavylium ions to sulfonatocalix[4]arene and implication in the
photorelease of biologically relevant guests in water, J. Org. Chem. 84 (2019) 10852-
10859. https://doi.org/10.1021/acs.joc.9b01420
[20] P. Todorov, P. Peneva, S. Georgieva, J. Tchekalarova, V. Vitkova, K. Antonova, A.
Georgiev, Synthesis, characterization and anticonvulsant activity of new azobenzene-
containing UV-hemorphin-5 bio photoswitch, Amino Acids 51 (2019) 549-563.
https://doi.org/10.1007/s00726-018-02691-1
[21] I. Turan, G. Gunaydin, S. Ayan, E. Akkaya, 2018. Molecular demultiplexer as a
terminator automaton. Nat. Commun. 9, 805. https://doi.org/10.1038/s41467-018-
03259-z
[22] T. Kelly, Progress toward a rationally designed molecular motor, Acc. Chem. Res. 34
(2001) 514-522. https://doi.org/10.1021/ar000167x
[23] G. Kottas, L. Clarke, D. Horinek, J. Michl, Artificial molecular rotors, Chem. Rev.
105 (2005) 1281-1376. https://doi.org/10.1021/cr0300993

[24] E. Kay, D. Leigh, F. Zerbetto, Synthetic molecular motors and mechanical machines,
Angew. Chem. Int. Ed. 46 (2007) 72-191. https://doi.org/10.1002/anie.200504313
[25] Q. Zhang, S-J. Rao, T. Xie, X. Li, T-Y. Xu, D-W. Li, D-H. Qu, Y-T. Long, H. Tian,
Muscle-like artificial molecular actuators for nanoparticles, Chem 4 (2018) 2670-
2684. https://doi.org/10.1016/j.chempr.2018.08.030
[26] C. Bruns, J. Stoddart, Rotaxane-based molecular muscles, Acc. Chem. Res. 47 (2014)
2186-2199. https://doi.org/10.1021/ar500138u
[27] B. Juluri, A. Kumar, Y. Liu, T. Ye, Y-W. Yang, A. Flood, L. Fang, J. Stoddart, P.
Weiss, T. Huang, A mechanical actuator driven electrochemically by artificial
molecular muscles, ACS Nano 3 (2009) 291-300. https://doi.org/10.1021/nn8002373
[28] J. Callan, A. de Silva, D. Magri, Luminescent sensors and switches in the early 21st
century, Tetrahedron 61 (2005) 8551-8588. https://doi.org/10.1016/j.tet.2005.05.043
[29] B. Valeur, I. Leray, Design principles of fluorescent molecular sensors for cation
recognition, Coord. Chem. Rev. 205 (2000) 3-40. https://doi.org/10.1016/S0010-
8545(00)00246-0
[30] S. Erbas-Cakmak, S. Kolemen, A. Sedgwick, T. Gunnlaugsson, T. James, J. Yoon, E.
Akkaya, Molecular logic gates: the past, present and future, Chem. Soc. Rev. 47
(2018) 2228-2248. https://doi.org/10.1039/C7CS00491E
[31] V. Bojinov, N. Georgiev, Molecular sensors and molecular logic gates, J. Univ. Chem.
Technol. Metall. 46 (2011) 3-26. https://dl.uctm.edu/journal/web/j2011-1
[32] M. Budyka, Design principles and action of molecular logic gates, Russ. Chem. Bull.
63 (2014) 1656-1665. https://doi.org/10.1007/s11172-014-0651-2
[33] H. Singh, G. Bhargava, S. Kumar, P. Singh, Quadruple-signaling (PET, ICT, ESIPT,
CN rotation) mechanism-based dual chemosensor for detection of Cu2+ and Zn2+ ions:
TRANSFER, INH and complimentary OR/NOR logic circuits, J. Photochem.
Photobiol. A: Chem. 357 (2018) 175-184.
https://doi.org/10.1016/j.jphotochem.2018.02.030
[34] N. Georgiev, A. Sakr, V. Bojinov, Design and synthesis of a novel PET and ICT based
1,8-naphthalimide FRET bichromophore as a four-input Disabled–Enabled-OR logic
gate, Sens. Actuators B: Chem. 221 (2015) 625-634.
https://doi.org/10.1016/j.snb.2015.07.009
[35] N. Georgiev, M. Dimitrova, Y. Todorova, V. Bojinov, Synthesis, chemosensing
properties and logic behaviour of a novel ratiometric 1,8-naphthalimide probe based

on ICT and PET, Dyes Pigm. 131 (2016) 9-17.
https://doi.org/10.1016/j.dyepig.2016.03.051
[36] J. Qian, X. Qian, Y. Xu, S. Zhang, Multiple molecular logic functions and molecular
calculations facilitated by surfactant's versatility, Chem. Commun. (2008) 4141-4143.
https://doi.org/10.1039/B805876H
[37] D. Margulies, G. Melman, A. Shanzer, A molecular full-adder and full-subtractor, an
additional step toward a moleculator, J. Am. Chem. Soc. 128 (2006) 4865-4871.
https://doi.org/10.1021/ja058564w
[38] M. Elstner, A. Schiller, Playing Tic-Tac-Toe with a sugar-based molecular computer,
J. Chem. Inf. Model. 55 (2015) 1547-1551. https://doi.org/10.1021/acs.jcim.5b00324
[39] Y. Shirai, J-F. Morin, T. Sasaki, J. Guerrero, J. Tour, Recent progress on
nanovehicles, Chem. Soc. Rev. 35 (2006) 1043-1055.
https://doi.org/10.1039/B514700J
[40] W. Chen, C. Guo, Q. He, X. Chi, V. Lynch, Z. Zhang, J. Su, H. Tian, J. Sessler,
Molecular cursor caliper: A fluorescent sensor for dicarboxylate dianions, J. Am.
Chem. Soc. 141 (2019) 14798-14806. https://doi.org/10.1021/jacs.9b07170
[41] S. Slavcheva, J. Mendoza, S. Stanimirov, I. Petkov, N. Basílio, F. Pina, V. Petrov, On
the multistate of 2′-hydroxyflavylium-flavanone system. Illustrating the concept of a
timer with reset at the molecular level, Dyes Pigm. 158 (2018) 465-473.
https://doi.org/10.1016/j.dyepig.2018.05.066
[42] A. Buryak, F. Zaubitzer, A. Pozdnoukhov, K. Severin, Indicator displacement assays
as molecular timers, J. Am. Chem. Soc. 130 (2008) 11260-11261.
https://doi.org/10.1021/ja8037118
[43] T. Sarkar, K. Selvakumar, L. Motiei, D. Margulies, 2016. Message in a molecule. Nat.
Commun. 7, 11374. https://doi.org/10.1038/ncomms11374
[44] D. Tong, H. Duan, H. Zhuang, J. Cao, Z. Wei, Y. Lin, Using T-Hg-T and C-Ag-T: a
four-input dual-core molecular logic gate and its new application in cryptography,
RSC Adv. 4 (2014) 5363-5366. https://doi.org/10.1039/C3RA44650F
[45] V. Balzani, G. Bergamini, P. Ceroni, Light: A very peculiar reactant and product,
Angew. Chem. Int. Ed. 54 (2015) 11320-11337.
https://doi.org/10.1002/anie.201502325
[46] V. Balzani, A. Credi, M. Venturi, Photochemical conversion of solar energy,
ChemSusChem 1 (2008) 26-58. https://doi.org/10.1002/cssc.200700087

[47] X. Fan, R. Tian, S. Liu, S. Qiao, Q. Luo, T. Yan, S. Fu, X. Zhang, J. Xu, J. Liu,
Covalently assembled polymer nanocapsules: a novel scaffold for light-harvesting,
Polym. Chem. 9 (2018) 1160-1163. https://doi.org/10.1039/C7PY02068F
[48] T. Mirkovic, E. Ostroumov, J. Anna, R. van Grondelle, R. Govindjee, G. Scholes,
Light absorption and energy transfer in the antenna complexes of photosynthetic
organisms, Chem. Rev. 117 (2017) 249-293.
https://doi.org/10.1021/acs.chemrev.6b00002
[49] M. Baroncini, S. Silvi, A. Credi, Photo- and redox-driven artificial molecular motors,
Chem. Rev. 120 (2020) 200-268. https://doi.org/10.1021/acs.chemrev.9b00291
[50] O. Bushuyev, M. Aizawa, A. Shishido, C. Barrett, 2018. Shape-shifting azo dye
polymers: Towards sunlight-driven molecular devices. Macromol. Rapid Commun.
39, 1700253. https://doi.org/10.1002/marc.201700253
[51] S. Everhart, U. Jayasundara, H. Kim, R. Procfflpez-Schtirbu, W. Stanbery, C. Mishler,
B. Frost, J. Cline, T. Bell, Synthesis and photoisomerization of substituted
dibenzofulvene molecular rotors, Chem. Eur. J. 22 (2016) 11291-11302.
https://doi.org/10.1002/chem.201600854
[52] S. Sasaki, G. Drummen, G. Konishi, Recent advances in twisted intramolecular charge
transfer (TICT) fluorescence and related phenomena in materials chemistry, J. Mater.
Chem. C 4 (2016) 2731-2743. https://doi.org/10.1039/C5TC03933A
[53] T. Liu, X. Liu, D. Spring, X. Qian, J. Cui, Z. Xu, 2015. Quantitatively mapping
cellular viscosity with detailed organelle information via a designed PET fluorescent
probe. Sci. Rep. 4, 5418. https://doi.org/10.1038/srep05418
[54] M. Koenig, B. Storti, R. Bizzarri, D. Guldi, G. Brancato, G. Bottari, A fluorescent
molecular rotor showing vapochromism, aggregation-induced emission, and
environmental sensing in living cells, J. Mater. Chem. C 4 (2016) 3018-3027.
https://doi.org/10.1039/C5TC03541D
[55] Q. Zhao, C. Yin, J. Kang, Y. Wen, F. Huo, A viscosity sensitive azide-pyridine
BODIPY-based fluorescent dye for imaging of hydrogen sulfide in living cells, Dyes
Pigm. 159 (2018) 166-172. https://doi.org/10.1016/j.dyepig.2018.06.029
[56] H. Zhang, Y. Qu, K. Zhao, C. Wang, Y. Wu, H. Wu, A fluorescence “on-off” sensor
for the highly selective and sensitive detection of Cu2+ ion, J. Chin. Chem. Soc. 67
(2020) 1062-1069. https://doi.org/10.1002/jccs.201900337

[57] G. Saito, D. Velluto, M. Resmini, 2018. Synthesis of 1,8-naphthalimide-based probes
with fluorescent switch triggered by flufenamic acid, R. Soc. Open Sci. 5, 172137.
https://doi.org/10.1098/rsos.172137
[58] P. Panchenko, Y. Fedorova, O. Fedorova, Selective fluorometric sensing of Hg2+ in
aqueous solution by the inhibition of PET from dithia-15-crown-5 ether receptor
conjugated to 4-amino-1,8-naphthalimide fluorophore, J. Photochem. Photobiol. A:
Chem. 364 (2018) 124-129. https://doi.org/10.1016/j.jphotochem.2018.06.003
[59] N. Marinova, N. Georgiev, V. Bojinov, Synthesis and photophysical properties of
novel 1,8-naphthalimide lightharvesting antennae based on benzyl aryl ether
architecture, J. Lumin. 204 (2018) 253-260.
https://doi.org/10.1016/j.jlumin.2018.08.011
[60] N. Marinova, N. Georgiev, V. Bojinov, Design, synthesis and pH sensing properties of
novel 1,8-naphtalimide-based bichromophoric system, J. Photochem. Photobiol. A:
Chem. 222 (2011) 132-140. https://doi.org/10.1016/j.jphotochem.2011.05.012
[61] J. Morris, M. Mahaney, J. Huber, Fluorescence quantum yield determinations 9,10-
diphenylanthracene as a reference-standard in different solvents, J. Phys. Chem. 80
(1976) 969-974. https://doi.org/10.1021/j100550a010
[62] N. Georgiev, V. Bojinov, The design and synthesis of a novel 1,8-naphthalimide
PAMAM light-harvesting dendron with fluorescence “off-on” switching core, Dyes
Pigm. 84 (2010) 249-256. https://doi.org/10.1016/j.dyepig.2009.09.013
[63] M. McKenna, I. Grabchev, P. Bosch, The synthesis of a novel 1,8-naphthalimide
based PAMAM-type dendron and its potential for light-harvesting, Dyes Pigm. 81
(2009) 180-186. https://doi.org/10.1016/j.dyepig.2008.09.008
[64] N. Georgiev, V. Bojinov, Design, synthesis and photostability of novel 1,8-
naphthalimide PAMAM light-harvesting dendrons, J. Fluoresc. 21 (2011) 51-63.
https://doi.org/10.1007/s10895-010-0689-y
[65] N. Yesilgul, O. Seven, R. Guliyev, E. Akkaya, Energy harvesting in a Bodipy-
functionalized rotaxane, J. Org. Chem. 83 (2018) 13228-13232.
https://doi.org/10.1021/acs.joc.8b01928
[66] Z-Y. Wu, J-N. Cui, X-H. Qian, T-Y. Liu, A 4-aminonaphthalimide based
environmentally sensitive fluorescence probe, Chin. Chem. Lett. 24 (2013) 359-361.
https://doi.org/10.1016/j.cclet.2013.03.027
[67] N. Georgiev, A. Asiri, A. Qusti, K. Alamry, V. Bojinov, Design and synthesis of pH-
selective fluorescence sensing PAMAM light-harvesting dendrons based on 1,8-

naphthalimides, Sens. Actuators B: Chem. 190 (2014) 185-198.
https://doi.org/10.1016/j.snb.2013.08.074
[68] Z. Szakacs, S. Rousseva, M. Bojtar, D. Hessz, I. Bitter, M. Kallay, M. Hilbers, H.
Zhang, M. Kubinyi, Experimental evidence of TICT state in 4-piperidinyl-1,8-
naphthalimide - a kinetic and mechanistic study, Phys. Chem. Chem. Phys. 20 (2018)
10155-10164. https://doi.org/10.1039/C7CP08555A
[69] Y. Chen, J. Qi, J.Huang, X. Zhou, L. Niu, Z. Yan, J. Wang, A nontoxic, photostable
and high signal-to-noise ratio mitochondrial probe with mitochondrial membrane
potential and viscosity detectivity, Spectrochim. Acta Part A 189 (2018) 634-641.
https://doi.org/10.1016/j.saa.2017.08.063
[70] S. Lynch, T. Rice, T. Moody, H. Gunaratne, A. de Silva, Structural effects on the pH-
dependent fluorescence of naphthalenic derivatives and consequences for
sensing/switching, Photochem. Photobiol. Sci. 11 (2012) 1675-1681.
https://doi.org/10.1039/C2PP25069A
[71] W. Chi, J. Chen, Q. Qiao, Y. Gao, Z. Xu, X. Liu, Revealing the switching mechanisms
of an OFF-ON-OFF fluorescent logic gate system, Phys. Chem. Chem. Phys. 21
(2019) 16798-16803. https://doi.org/10.1039/C9CP01401B
[72] J. Spiteri, A. Johnson, S. Denisov, G. Jonusauskas, N. McClenaghan, D. Magri, A
fluorescent AND logic gate based on a ferrocene-naphthalimide-piperazine format
responsive to acidity and oxidizability, Dyes Pigm. 157 (2018) 278-283.
https://doi.org/10.1016/j.dyepig.2018.04.060
[73] V. Pais, P. Remón, D. Collado, J. Andréasson, E. Pérez-Inestrosa, U. Pischel, OFF-
ON-OFF fluorescence switch with T-latch function, Org. Lett. 13 (2011) 5572-5575.
https://doi.org/10.1021/ol202312n
[74] M. Poddar, G. Sivakumar, R, Misra, Donor-acceptor substituted 1,8-naphthalimides:
design, synthesis, and structure-property relationship, J. Mater. Chem. C 7 (2019)
14798-14815. https://doi.org/10.1039/C9TC02634G
[75] V. Bojinov, N. Georgiev, P. Nikolov, Synthesis and photophysical properties of
fluorescence sensing ester- and amidoamine-functionalized 1,8-naphthalimides, J.
Photochem. Photobiol. A: Chem. 193 (2008) 129-138.
https://doi.org/10.1016/j.jphotochem.2007.06.016
[76] W-S. Li, M-J. Teng, X-R. Jia, B-B. Wang, J-M. Yeh, Synthesis and energy transfer
properties of poly(amidoamine) dendrons modified with naphthyl and dansyl groups,
Tetrahedron Lett. 49 (2008) 1988-1992. https://doi.org/10.1016/j.tetlet.2008.01.083

[77] M. Haidekkera, E. Theodorakis, Molecular rotors-fluorescent biosensors for viscosity
and flow, Org. Biomol. Chem. 5 (2007) 1669-1678.
https://doi.org/10.1039/B618415D

Tables
Table 1
Absorption and fluorescent characteristics of compounds 3, 6 and 7 in different solvents.
Compound
3
6
7
Solvent
λA (nm)
λF (nm)
λA (nm)
λF (nm)
λA (nm)
λF (nm)
ФF
362
398
418
498
Chloroform
Acetonitrile
Ethanol
360
358
360
360
419
400
398
398
400
500
0.16
358
400
425
519
429
429
433
523
521
518
0.07
0.02
0.01
360
402
434
523
360
402
434
516
DMF

Figure legends
Fig. 1. 1H NMR spectrum of light harvesting rotor 7 in chloroform.
Fig. 2. Absorption spectra of compounds 3, 6 and 7 in chloroform solution.
Fig. 3. Normalized to the optical density fluorescent spectra of compounds 3, 7 (excited at
360 nm) and 6 (excited at 400 nm) in chloroform solution.

Fig. 4. Fluorescent spectra of antenna 7 in glycol (black line), glycol/glycerol = 4:1 v/v (red
line), glycol/glycerol = 1:1 v/v (blue line), glycol/glycerol = 1:4 v/v (green line) and glycerol
(navy line).
Fig. 5. Fluorescent spectra of antenna 7 in glycol and glycerol containing 10 µM acetate
buffer (pH 4.5).

Fig. 6. Absorption spectra of antenna 7 in water/DMF solution (1:1, v/v) at different pHs.
Fig. 7. Fluorescent spectra of antenna 7 in water/DMF solution (1:1, v/v) at different pHs (λex
= 360 nm).

Scheme 1. Multifunctional light-harvesting system 7.
Scheme 2. Synthesis of multifunctional light-harvesting system 7.

Scheme 3. Photophysical behaviour of light-harvesting system 7 as a function of pH.