Study of modulating opto-electrochemical properties in Suzuki coupled phenazine derivatives for organic electronics

Article abstract of DOI:10.1007/s11696-021-01772-y

In this work, five 3,6,11-trisubstituted-dibenzo[a,c]phenazine (2–6) derivatives were synthesized by employing Palladium-catalyzed Suzuki–Miyaura ‘C–C bond’ coupling reaction and characterized. Absorption spectra of 2–6 show the formation of charge-transfer complexes. Dyes exhibit blue-green fluorescence with emission maxima 434–506?nm in various solvents and neat solid film. To elucidate AIE phenomenon, photophysical properties of dye 2 and 3 in different THF/water mixture were studied. The HOMO and LUMO energy level were found in the range of ? 6.38 to ? 6.82?eV and ? 3.67 to ? 3.75?eV with an electrochemical bandgap of 2.71–3.08?eV. The HOMO and LUMO distribution in molecules were further studied by DFT/TD–DFT calculations. Herein, characteristic blue emission, comparable energy levels with n-type materials, and good thermal stability of derivatives make them a potential candidate for their application in optoelectronics. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11696-021-01772-y

Chemical Papers
https://doi.org/10.1007/s11696-021-01772-y
ORIGINAL PAPER
Study of modulating opto‑electrochemical properties in Suzuki
coupled phenazine derivatives for organic electronics
1
1
1
Deepali N. Kanekar · Purav M. Badani · Rajesh M. Kamble
Received: 15 February 2021 / Accepted: 1 July 2021
©
Institute of Chemistry, Slovak Academy of Sciences 2021
Abstract
In this work, fve 3,6,11-trisubstituted-dibenzo[a,c]phenazine (2–6) derivatives were synthesized by employing Palladium-
catalyzed Suzuki–Miyaura ‘C–C bond’ coupling reaction and characterized. Absorption spectra oꢀ 2–6 show the ꢀormation
oꢀ charge-transꢀer complexes. Dyes exhibit blue-green ꢁuorescence with emission maxima 434–506 nm in various solvents
and neat solid flm. To elucidate AIE phenomenon, photophysical properties oꢀ dye 2 and 3 in diꢂerent THF/water mixture
were studied. The HOMO and LUMO energy level were ꢀound in the range oꢀ−6.38 to−6.82 eV and−3.67 to−3.75 eV
with an electrochemical bandgap oꢀ 2.71–3.08 eV. The HOMO and LUMO distribution in molecules were ꢀurther studied
by DFT/TD–DFT calculations. Herein, characteristic blue emission, comparable energy levels with n-type materials, and
good thermal stability oꢀ derivatives make them a potential candidate ꢀor their application in optoelectronics.
Graphic abstract
Extended author inꢀormation available on the last page oꢀ the article
Vol.:(0
1
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Chemical Papers
Keywords Donor–acceptor system · Suzuki–Miyaura coupling · Photophysical studies · Aggregation-induced emission
AIE) · HOMO and LUMO energy level · n-type materials
(
Introduction
caused quenching, and relatively high-cost processing (Chi
and Chou 2010; Huang et al 2014).
In the last three decades, tremendous eꢂorts have been put
into the development oꢀ diꢂerent organic semiconducting
materials due to their various applications as organic light-
emitting diodes (OLEDs) (Friend et al. 1999; Baldo et al.
On the other side, the charge transꢀer property oꢀ dye is
also an important aspect to consider ꢀor its application in
optoelectronics. According to past reports, the development
oꢀ electron-transporting (n-type) materials is lagging much
behind compared to hole-transporting materials (p-type) due
to their diꢃcult synthesis and instability in the presence oꢀ
moisture (H2O) and oxygen (O2). However, n-type materi-
als are an indispensable component oꢀ the electronic circuit
(Meijer et al. 2003; Zhou et al. 2014) and need to get synthe-
sized ꢀor the development oꢀ organic electronics.
2
000), organic feld-eꢂect transistors (OFETs) (Anthony
et al. 2008), dye-sensitized solar cells (DSSCs) (Grätzel
et al. 2009; Imahori et al. 2009), sensors (Jiao et al. 2003;
Doré et al. 2004), nonlinear optics (Staub et al. 2003),
organic storage media (Zhou et al. 2018), etc. Among the
diꢀꢀerent types (small, polymer, and organometallic) oꢀ
organic semiconductors, D–A-based small organic mol-
ecules drawn considerable research interest because oꢀ their
notable properties such as well-defned structures, ease oꢀ
purifcation, simple structure modulation, good thermal sta-
bility, and unique charge transꢀer properties. These allow
tuning oꢀ optoelectronic properties through structure modu-
lation/modifcation. The combination oꢀ strong donor and
acceptor in the D–A system mostly includes diꢂerent amines
like triarylamine/diarylamine, heterocyclic amines, aliphatic
amines as donors, and diꢂerent N-embedded rings like qui-
noxaline (Lee et al. 1999; Thomas et al. 2002; Shaikh et al.
To meet the mentioned need ꢀor eꢃcient luminescence
and electron transport, several strategies are used in the lit-
erature. For example, the incorporation oꢀ electronegative
heteroatoms like N or S to acceptor core or introduction oꢀ
electron-withdrawing groups such as –F, –CN, –Cl, –NO2,
–COOH, –CF3, perꢁuorinated alkyl chain in hole-transport-
ing materials can help to covert p-type material to n-type
material (Winkler and Houk 2007). Nonetheless, the ability
oꢀ the D–A system to induce a twist in the structure oꢀ the
molecule helps to tackle the problem oꢀ aggregation quench-
ing. These molecules restrict intramolecular rotation, thus
prevent the ꢀormation oꢀ detrimental species like exciplexes
and excimers and enable molecules to emit in aggregation/
solid-state (Furue et al 2016). Additionally, the introduction
oꢀ bulky donor groups or integration oꢀ AIE units to conven-
tional ACQ ꢁuorophores has been an eꢂective approach to
solve the ACQ problem and can induce luminescence into
new ꢁuorophores (Yuan et al. 2010).
2
015, 2016a, 2016b; Sharma et al. 2017; Kamble et al. 2018;
Kanekar et al. 2019; Singh et al. 2019a, b; Mahadik et al.
019), pyrazine (Xu et al. 2015a, b; Mahadik et al. 2021),
2
and phenazines (Okamoto et al. 2003; Wang et al. 2013;
Shaikh et al. 2016c, 2017; Kanekar et al. 2018, 2020) as
acceptor where the use oꢀ strong donor and acceptor leads
to large charge separation, that is, responsible ꢀor strong
intramolecular charge transꢀer (ICT) character in the dye
and shiꢀts dye emission at a longer wavelength in the yel-
low–red region. On the other side, the use oꢀ aryl derivatives
as a donor in C–C coupled molecules can bring small charge
separation in the molecule that leads to weak charge transꢀer
transitions and shiꢀts emission oꢀ dye at a shorter wavelength
in the blue-green region. Also, it has seen the luminophores
that exhibit good emission in dilute solution get quenched
on aggregation/in solid state. The development oꢀ solid-state
emissive materials is necessary ꢀor real-world applications
Thereꢀore, by considering these speciꢀic demands oꢀ
the photophysical and electrochemical characteristics oꢀ
organic ꢁuorophores, we have designed and synthesized
C–C-coupled D–A-based benzo[a,c]phenazine deriva-
tives by Suzuki–Miyaura coupling reaction (Miyaura et al.
1981, 2002; Negishi et al. 2002). Herein, phenazine acts
as an eꢃcient acceptor core due to the presence oꢀ two
electron-withdrawing N-atoms in the tricyclic system and
the extended conjugation. Among the diꢂerent electron-
defcient azaacenes core, very ꢀew reports have appeared
on the development oꢀ phenazines and their derivatives in
optoelectronic applications. This suggests the necessity oꢀ
its investigation and scope in the development oꢀ phena-
zine derivatives in organic electronics. More specifcally,
the available reports on acceptor moiety dibenzo[a,c]phena-
zines in the literature include dihydrophenazine derivatives
(Okamoto et al. 2003; Zheng et al. 2014), electroluminescent
D–A-based dibenzophenazines as hole transporters (Shaikh
et al. 2016b), D–A–D-based red dibenzo[a,c]phenazine
(
Mullen and Scherꢀ 2006; Furue et al. 2016). Particularly,
the blue materials are the key ꢀactor that inꢁuences the ꢀoun-
dation oꢀ OLED applications as they can oꢂer a wide gamut
RGB (red, green, and blue) color space. Thus, blue materials
can be employed as an excitation source to activate emis-
sions oꢀ other colors through energy transꢀer (Hung et al.
2
002; Qin et al. 2015). However, compared to orange-red
luminophores blue-green luminophores are rare as they ꢀace
problems such as low eꢃciency, short liꢀetime, aggregation
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Chemical Papers
ꢁ
uorophores (He et al. 2015), tetrabranched dibenzophena-
phenazine (1) core through C–C coupling on photophysi-
cal and electrochemical properties. In this structure assem-
bly, the occurrence oꢀ charge transꢀer at a shorter wave-
length has expected so that dyes can exhibit emission in
the blue-green region. Further, the eꢂect oꢀ substitution
zine derivatives (Boxi et al. 2018), and the recent research
on the analysis oꢀ ITO surꢀace modifed with selꢀ-assembled
dibenzophenazine carboxylic group (Havare 2020).
Taking the ability to tune the optoelectronic properties
oꢀ an organic molecule through simple molecular modu-
lation into account, herein we studied the eꢂect oꢀ the
modifed structural ꢀramework oꢀ dibenzo[a,c]phenazine
derivatives obtained by attaching diꢂerent aryl donors
at 3rd, 6th, and 11th position oꢀ acceptor dibenzo[a,c]
with electron-donating (EDG) –OCH and withdrawing
3
(EWG) –CN group on peripheral aryl segment on the opto-
electrochemical properties such as intramolecular charge
transꢀer transition (ICT), HOMO–LUMO energy levels
and band gap has been studied. The structures oꢀ synthe-
sized molecules 2–6 are shown in Fig. 1.
Fig. 1 Molecular structure oꢀ compounds 2–6
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Chemical Papers
Results and discussion
Photophysical Properties
Synthesis and characterization
The photophysical properties oꢀ 2–6 were investigated in
various solvents and neat solid flm by using UV–Visible
and ꢁuorescence spectroscopy in order to understand the
optical profle oꢀ dyes and their alteration due to changing
polarity oꢀ solvents (toluene, chloroꢀorm, DCM, and DMSO)
and in a neat solid flm. The UV–Vis absorption spectra
oꢀ compounds 2–6 in toluene and DCM are presented in
Fig. 2a and b, while the pertinent data are summarized in
Table 1 (See supporting inꢀormation (SI): Figure S1). The
transitions around 282–408 nm in absorption spectra oꢀ par-
ent 3,6,11-tribromodibenzo[a,c]phenazine (1) correspond to
Compound 1 was prepared according to the reported
procedure (Shaikh et al. 2017, Xie et al. 2020) and con-
frmed by MALDI-TOF. Compounds 2–6 were obtained by
Suzuki–Miyaura coupling reaction (Miyaura et al. 1981,
2
002; Negishi et al. 2002) oꢀ 1 with the corresponding aryl
boronic acid in the presence oꢀ Pd (dba) catalyst and SPhos
2
3
ligand in a mixture oꢀ aqueous 2 M K CO and toluene (1:3).
2
3
The synthesized compounds 2–6 were obtained in moder-
ate 30–50% yield as greenish-red solids soluble in com-
mon organic solvents including toluene, dichloromethane
*
*
n–π and π–π transitions (Figure S1a and Table S1).
Similarly, the multiple overlapping bands observed in
absorption spectra oꢀ 2–6 in the above-mentioned solvents
(
DCM), chloroꢀorm, tetrahydroꢀuran (THF), dimethyl sul-
ꢀ
oxide (DMSO). However, they are completely insoluble in
*
*
water. These target molecules were characterized by various
at 254–336 nm due to n–π and π–π transitions occurring in
the entire molecule whereas the lower energy band around
372–439 nm ꢀound to be aꢂected due to modulating periph-
eral aryl segment, could be assigned to charge transꢀer (CT)
transitions ꢀrom peripheral aryl donor to an acceptor phena-
zine as core (Misra and Bhattacharyya, 2018).
1
13
spectroscopic technique such as FT–IR, H, C–NMR spec-
troscopy, MALDI–TOF mass spectrometry, and elemental
analysis. The synthetic route oꢀ compounds 2–6 is shown
in Scheme 1.
To understand the eꢂect oꢀ diꢂerent aryl donors, optical
properties oꢀ derivatives were compared within with deriva-
tive 2. The notable redshiꢀt oꢀ 10–13 nm ꢀor CT transitions
in 4 attributed to increased donating strength oꢀ donor due to
Scheme 1 Synthetic route oꢀ 2–6
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Chemical Papers
Fig. 2 UV−Vis absorption (above) and emission spectra (below) oꢀ compounds 2−6 in toluene (a) and (A) and dichloromethane (b) and (B)
the presence oꢀ electron-donating–OCH group in the mole-
maxima in the range 434–497 nm in toluene, chloroꢀorm,
DCM, and DMSO (Fig. 2a and b and SI Figure S2). Emis-
sion spectra oꢀ compounds in various solvents display
bathochromic shiꢀt oꢀ 21–49 nm in compound 4 that could
be attributed to the presence oꢀ electron-donating –OCH3 in
group on peripheral phenyl segment. Conversely, the emis-
sion oꢀ dyes 5 and 6 was considerably quenched throughout
the solution, suggests ineꢃcient interaction between donor
segment and acceptor core that might be due to the pres-
ence oꢀ electron-withdrawing–CN group on donor entity in 5
and poor electron-donating strength oꢀ quinoline in 6. Blue-
shiꢀted emission ꢀor low emitting dye 5 and 6 compared to
2 can be observed in the inset (Fig. 2a and b) and witnesses
the eꢂect oꢀ electron-withdrawing group (–CN group and
quinoline) on emission.
3
cule. Equally, the hypsochromic shiꢀt oꢀ 25–32 nm in 5 and 6
has been observed which can relate to the presence oꢀ strong
electron-withdrawing–CN group and quinoline, respectively.
However, the absorption maxima oꢀ all the molecules pos-
sess good molar absorptivity in solution and are ꢀound to be
unaꢂected by solvent polarity. This indicates that the dipole
moment oꢀ the ground state remains unaꢂected on increase
in solvent polarity (Lakowicz 2006). The optical band gap
oꢀ all derivatives obtained ꢀrom the oꢂset wavelength was
derived ꢀrom the low energy absorption band and is in the
range oꢀ 2.64–3.08 eV which is comparable with the optical
band gap oꢀ reported blue-emitting organic semiconductors
(
Misra et al. 2004).
The other photophysical ꢀactors such as emission data,
optical band gap, Stoke’s shiꢀt, and quantum yield are cal-
culated and summarized in Table 1. The emission spectra oꢀ
The shiꢀt in emission maxima oꢀ dyes has been observed
on changing solvent and suggests the sensitivity oꢀ emis-
sion oꢀ dyes toward the environmental ꢀactors oꢀ solvents.
The noticeable bathochromic shiꢀt on increasing polarity
2
2
–6 were obtained on excitation at their CT maxima. Dyes
–4 exhibit blue–cyan blue ꢀluorescence with emission
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Chemical Papers
Table 1 UV–vis and photoluminescence (PL) spectroscopic parameters oꢀ 2–6 in solution and neat solid state
Compounda
Medium
UV–vis
PL
Stoke’s shiꢀt, (cm )
−1 e
λmax (nm), (log εmax)b
opt
(Eg , eV)
c
λem (nm)
(ꢀ F) d
(
(
(
(
5.34)
5.40)
5.43)
6.00)
, 404 (4.76), 422
(4.82)
2
Toluene
CHCl3
DCM
DMSO
FILM
Toluene
CHCl3
DCM
DMSO
FILM
Toluene
CHCl3
DCM
DMSO
FILM
Toluene
CHCl3
DCM
DMSO
FILM
282
289
281
264
2.86
2.82
2.83
2.78
2.67
2.84
2.84
2.79
2.68
2.67
2.74
2.71
2.71
2.64
2.62
3.08
3.05
3.07
3.04
2.92
3.07
3.06
3.08
3.04
2.90
434, 459
442, 465
441, 463
448, 471
487
441
460
461
496
506
455, 482
474
0.15
0.26
0.20
0.07
–
0.22
0.46
0.39
0.23
–
0.39
0.49
0.48
0.42
–
0.00095
0.0015
0.0012
0.0021
–
655, 1910
1299, 2241
1191, 2268
1152, 2242
2560
1478
2474
2521
3819
4568
1170,2401
2105
2095
2658
2843
1653
1748
1925
2444
1691
(4.99)
(4.76)
(5.35)
(4.99)
(4.77)
, 403
, 402
, 289
, 418
, 419
, 406(4.90), 426(4.91)
292, 368, 412, 433
(
(
(
(
5.73)
5.35)
5.65)
5.46)
(4.88)
(4.85)
(5.45)
(5.47)
(5.06)
(4.96)
(4.99)
(5.12)
3
4
5
6
284
294
263
293
, 395
, 394
, 294
, 296
, 414
, 413
, 392
, 417
, 413(5.12)
304, 411, 434
(
(
(
(
5.38)
5.64)
5.43)
5.48)
(5.45)
(5.72)
(5.51)
(4.97)
(4.61)
(5.15)
(5.77)
(5.83)
(4.77)
281
291
268
294
, 330
, 329
, 292
, 304
, 408
, 407
, 328
, 336
, 432
, 431
(5.22)
((5.46))
(5.13)
, 405
, 432
475
497
499
, 407(5.04), 439
(5.16)
304, 418, 437
(
(
(
(
5.43)
6.00)
5.65)
6.00)
(5.56)
(5.35)
(5.23)
(5.20)
(5.57)
(5.01)
(5.14)
(5.12)
(4.96)
282
254
280
258
, 311
, 311
, 309
, 310
, 372
, 373
, 372
, 374
, 393
, 393
, 392
, 394
420
(5.06)
422
(5.21)
424
(5.18)
436
314, 380, 402
430
(
(
(
(
5.61)
6.00)
5.15)
5.95)
(5.14)
(5.27)
(5.12)
(5.02)
(5.23)
(5.26)
(5.20)
(5.09)
Toluene
CHCl3
DCM
DMSO
FILM
309
254
309
310
, 372
, 309
, 372
, 374
, 393
, 373
, 392
, 394
420
0.0027
0.0031
0.0015
0.0014
–
1653
1748
2091
2549
, 393(5.33)
422
427
438
380, 400
451
2827
a
Recorded in10−6 M solution
b
c
d
e
log εmax molar absorptivity in solution (M cm−1
−1
)
ꢀ
ꢁeV
opt
g
1240
Optical band gap estimated using oꢂset wavelength derived ꢀrom the low energy absorption band E
=
ꢀ
abs edge
Quantum yield with reꢀerence to ꢁuorescein (ꢀ=0.79 in 0.1 M NaOH)
Stoke’s shiꢀts calculated according to the equation ∆ν=(1/λabs −1/λem)×107 (cm−1)
The very low-intensity emission maxima oꢀ dyes are in bold.
oꢀ solvent ꢀrom toluene to DMSO correspondingly shiꢀts
dyes in various solvents, we evaluated Lippert–Mattaga’s
plot (Mattaga et. al 1956; Lippert 1957) and Weller’s plot
(Weller 1956) oꢀ dyes. Lippert–Mattaga plot (Fig. 3c) is the
plot oꢀ Stoke’s shiꢀt vs orientation polarizability (∆f) which
only accounts ꢀor general solvent eꢂects and not ꢀor spe-
cifc solute–solvent interaction such as π-electron involving
(π–π, π-cation, π-anion) or hydrogen-bonding interaction.
Lippert–Mattaga plot oꢀ dyes 2, 3, and 4 suggests that dye
3 and 4 are more sensitive to solvent polarity than dye 2.
However, deviation ꢀrom the general solvent eꢂect indicates
the possibility oꢀ specifc solute–solvent interaction such
as H-bonding oꢀ dyes in chloroꢀorm and dichloromethane.
Further, Weller’s plot Fig. 3d which is a graph oꢀ emission
ꢁ
uorescence oꢀ 2–4 ꢀrom pure blue (λ
: 434–482 nm) to
Emax
blue–cyan blue region (λ
: 448–497 nm) and indicates
Emax
the decrease in the energy gap (ΔE) between the ground
state and the excited state gradually with the increase in
the solvent polarity. This redshiꢀt in the emission oꢀ dyes
ꢀ
rom non-polar toluene to polar DMSO also suggests the
transition in the maniꢀestation oꢀ emission ꢀrom the lowest
excited state (LE) to charge transꢀer state on photoexcita-
tion (Fig. 3b). One can easily see the bathochromic shiꢀt in
emission obtained on increasing polarity oꢀ solvent ꢀor dyes
through Fig. 3a and b (Reichardt 2002). Though all three
dyes (2–4) exhibit a bathochromic shiꢀt in the emission with
an increase in solvent polarity, their solute–solvent interac-
tions slightly diꢂer. To comprehend the polarity eꢂect oꢀ
−
1
maxima intensities (λ
) in cm versus Weller’s ꢀunc-
em max
tion (∆f ) shows evident charge transꢀer in an excited state
w
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Chemical Papers
Fig. 3 Solvent polarity eꢂect oꢀ dyes 2, 3 and 4 in various solvents
viz Toluene, chloroꢀorm, dichloromethane and DMSO on emission; a
Emission spectra oꢀ 4 in various solvents, b dependence oꢀ emission
plot oꢀ Stoke’s shiꢀt versus orientation polarizability oꢀ solvents (∆f),
(d) plot oꢀ emission wavelength oꢀ 2, 3, and 4 versus Weller ꢀunctions
(∆f )
w
maxima oꢀ 2, 3, and 4 on polarity parameters (E
) oꢀ solvents, (c)
T(30)
ꢀ
or D-A-based molecule. Weller’s plot oꢀ dyes 2–4 demon-
low emitting dye 5 and 6 are less than 0.01. Additionally,
−1
strates a linear relationship with good regression coeꢃcient
derivatives exhibit Stoke’s shiꢀt in the range 655–3819 cm
in various solvents.
2
R (0.63 ꢀor dye 2, 0.76 ꢀor dye 3, and 0.83 ꢀor dye 4). It
reveals the occurrence oꢀ charge transꢀer ꢀrom peripheral
donor segment to acceptor phenazine core which leads to
increased dipole moments oꢀ excited state compared to the
ground state in polar solvents.
Photophysical properties in solid state
To study optical properties in the solid state, a neat solid flm
oꢀ dyes was ꢀabricated by a spin coating oꢀ dye solution in
chloroꢀorm on a quartz plate (see an experimental section ꢀor
details). The absorption and emission spectra oꢀ 2–6 in the
solid flm are presented in Fig. 4. Likewise in solution, the
absorption spectra oꢀ 2–6 in the neat solid flm display the
The quantum yield oꢀ ꢁuorophore 2–6 in various sol-
vents was estimated by using ꢁuorescein (Ф=0.79 in 0.1 M
NaOH) as a reꢀerence (Table 1). The quantum yield oꢀ syn-
thesized dyes 2–4 was ꢀound in the range 0.07–0.49 in tolu-
ene, chloroꢀorm, DCM, and DMSO wherein comparatively
better quantum yields have been recorded in chloroꢀorm and
dichloromethane ꢀor dyes 2–4 which could be attributed to
specifc solute–solvent interaction that decreasing rate oꢀ
non-radiative decay or to a conꢀormational change in ꢁuo-
rophore (Lakowicz 2006). Besides this, quantum yields oꢀ
*
*
high energy n–π and π–π transitions around 292–314 nm,
and the transition observed at a longer wavelength ꢀrom
368 to 437 nm can be assigned CT transitions in the mol-
ecule (Table 1). Herein, the absorption profles observed
were broad and slightly red-shiꢀted as compared to solutions
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Chemical Papers
Fig. 4 Absorption a and emission spectra b oꢀ compounds 2−6 in a neat solid flm
which can be attributed to the molecular aggregation oꢀ dyes
on the surꢀace oꢀ the flm. On the other side, this molecular
aggregation was responsible ꢀor the decrease in lumines-
cence in dyes 2–6 except 3 wherein lowered emission inten-
sity was recorded ꢀor 2 and 5. A considerable quenching oꢀ
emission oꢀ 4 and 6 has been observed in a solid flm. Such
aggregation caused quenching in the solid state is a result
oꢀ ꢀast inter-chain electron transꢀer via close spatial contact
between the molecules (Sun and Sariciꢀtci, 2005).
been prepared by reported method to ꢀorm nanoparticles oꢀ
organic compounds (Kasai et al. 1992). The dye was frst
dissolved with THF as it is completely soluble in it, and
then, to this solution non-solvent water was slowly added to
–
5
obtain (10 M) suspension oꢀ aggregates.
These THF/water mixtures oꢀ compounds were observed
under 365 nm UV illumination in which the quenching oꢀ
emission at higher water ꢀraction has observed in 2, whereas
emission in case oꢀ 3 was considerably recovered at higher
water ꢀraction (Fig. 5). This suggests the occurrence oꢀ ACQ
in 2 that corresponds to its more planar geometry, wherein
3 recoveries oꢀ emission at higher water ꢀraction indicate
the presence oꢀ AIE activity (Birks 1970; Hong et al. 2011).
Thus, in order to understand this behavior oꢀ dye molecules
we have recorded the photoluminescence (PL) intensities oꢀ
THF/water mixtures oꢀ dyes.
The varying donating strength oꢀ peripheral aryl units
tunes the ꢁuorescence in 2–6 ꢀrom the blue to the green
region (λ
: 430–506 nm). In emission spectra oꢀ 2–6 in
Emax
neat solid flm, though some oꢀ the derivatives show weak
emission, the eꢂect oꢀ modulating donors is distinguish-
able. Dye 3 own noticeable redshiꢀt oꢀ 19 nm compared to 2
could be attributed to eꢂective conjugation oꢀ naphthalene
ring. Similarly, redshiꢀt (12 nm) oꢀ emission ꢀor dye 4 can
The photoluminescence (PL) spectra oꢀ 3 in diꢂerent
THF/water ꢀractions are presented in Fig. 5a (ꢀor 2 see SI,
Figure S3). The emission obtained in pure THF was attrib-
uted to CT ꢀrom the peripheral donor segment (biphenyl/
naphthalene) to acceptor phenazine core. Further, gradual
addition oꢀ water to THF increases the polarity oꢀ the solu-
tion that bathochromically shiꢀts emission ꢀrom blue to cyan
blue that indicates the occurrence oꢀ solvatoꢁuorochromism.
The distinct change in ꢀluorescence on the addition oꢀ
a small quantity oꢀ water in 3 displays better sensitivity oꢀ
dye ꢀor change oꢀ medium with water (Otsuki et al. 1993;
Jung et al. 2016). Thereaꢀter, the insolubility oꢀ dye in
water is responsible ꢀor lowering in emission intensity on
be assigned to the presence oꢀ the electron-donating–OCH
3
group. On the other side, the use oꢀ cyanobenzene and qui-
noline as a donor, blue-shiꢀted emission with 57 nm in 5
and 36 nm in 6 compared to 2 is due to the electron-with-
drawing eꢂect oꢀ the –CN group present on phenyl moiety
in 5 and quinoline in 6. Additionally, ꢁuorophores hold good
−
1
Stoke’s shiꢀt in the range 1691–4568 cm in a solid flm.
Further, the luminescence property oꢀ dyes in a solid/aggre-
gate state has been explored with AIE studies. For which we
have selected molecules 2 and 3, those have good emission
throughout in solution as well as in solid state to understand
aggregation eꢂect on the emission oꢀ dyes.
increasing water ꢀraction ꢀrom 50% ƒ which ꢀurther con-
w
Aggregation efect on emission:
siderably gets quenched at 60% ƒ . Further, the addition
w
oꢀ water shows a recovery oꢀ ꢀluorescence in the case oꢀ
Preliminary to understand aggregation eꢂect oꢀ 2 and 3,
3 ꢀrom 70 to 90% ƒ (Fig. 5b). This suggests the ꢀorma-
w
the THF/water mixtures (0–100%) oꢀ respective dyes have
tion oꢀ nano-aggregates that are responsible ꢀor improved
1
3

Chemical Papers
Fig. 5 Fluorescence spectra oꢀ 3 A, plots oꢀ PL intensity and peak wavelength versus water ꢀractions (f ) 3 B, and photographs oꢀ 3 in THF—
w
water mixture with increasing water ꢀractions (f ) C
w
emission, well known as AIE. In AIE, the ꢀormation oꢀ
nano-aggregates restricts the non-radiative decay process
such as intramolecular rotation and vibration and makes
luminogen emits eꢀꢀiciently (Hong et al. 2011). The vary-
ing emission intensity oꢀ nanosuspension was attributed
to a diꢀꢀerent physical constraint oꢀ molecule and yield
oꢀ nanoparticles obtained in nanosuspension (Liu et al.
suspension (Tong et al. 2006). This conꢀirms the presence
oꢀ AIE at a higher water ꢀraction due to the ꢀormation oꢀ
nanoparticles.
To confrm the ꢀormation oꢀ nano-aggregates at higher
water ꢀractions and to understand the size and morphology
oꢀ aggregates, we subjected suspension oꢀ luminophore 3
in THF/water mixture oꢀ 80% ƒ under a scanning electron
w
2
018). The AIE behavior oꢀ dye was ꢀurther explored
microscope (FEG-SEM). The SEM image oꢀ 3 (Fig. 6)
using absorption spectroscopy (see SI, Figure S4). In
in 80% ƒ displays that aggregate ꢀormed is spherical in
w
absorption spectra, level oꢀꢀ the tail or Mie scattering
nature with a mean diameter oꢀ 31–68 nm. The nanosus-
at a longer wavelength above 50% ƒ in 3 is the conse-
pension oꢀ 3 obtained was quite transparent and stable.
w
quence oꢀ scattering oꢀ light by nanoparticles ꢀormed in
1
3

Chemical Papers
Electrochemical properties
The electrochemical propensity and redox potential oꢀ the
derivatives were examined by cyclic voltammetry in DCM
with ꢀerrocene as an internal standard, and the pertinent data
are presented in Table 2. The cyclic voltammogram oꢀ 2
and 5 is presented in Fig. 7 (ꢀor other compounds, see SI
Figure S5).
On an anodic sweep, lower intensity oꢀ oxidation waves
leads to diꢃculty in the identifcation oꢀ proper oxidation
peaks in 1–6. On the other side, a cathodic sweep oꢀ 1–6
displays two predominant quasi-reversible waves that corre-
spond to the reduction in phenazine moiety through the two-
electron process (de la Cruz et al. 2020). All the derivatives
exhibit nearly similar redox behavior. However, the presence
oꢀ one extra reduction peak in compounds 5 and 6 could be
attributed to the reduction in peripheral cyanobenzene and
quinoline moiety, respectively.
Fig. 6 SEM image oꢀ nanoparticles oꢀ 3 obtained in nanoparticle sus-
pension containing 80% volume ꢀraction oꢀ water (ƒ ) in THF
w
It is important to know the HOMO and LUMO energy
levels oꢀ organic materials ꢀor their use in optoelectronics.
Thus, the LUMO energy level oꢀ 2–6 was calculated by frst
reduction potential, whereas the HOMO energy levels oꢀ
Table 2 Electrochemical data oꢀ 1–6
peak a
peak b
E
red
HOMOc LUMOd Ege
Compound
E
oxi
2
–6 were calculated ꢀrom the diꢂerence oꢀ optical band gap
1
2
3
4
5
6
–
–
–
–
–
–
−0.99, −1.47
−0.92,−1.34
−0.90,−1.32
−0.95,−1.30
−0.89,−1.41,−1.59 −6.82
−0.95,−1.39,−1.56 −6.76
−6.51
−6.53
−6.56
−6.38
−3.63 2.88
−3.70 2.83
−3.72 2.84
−3.67 2.71
−3.75 3.07
−3.68 3.08
obtained in DCM and LUMO energy values. The calcu-
lated HOMO and LUMO energy levels oꢀ 2–6 were ꢀound
in the range − 6.38 to − 6.82 eV and − 3.67 to − 3.75 eV.
Herein, the values oꢀ LUMO energy level below − 3.0 eV
suggest capability oꢀ electron transport (Jones et al. 2007;
Gao and Hu 2014) in derivatives with reꢀerence to reported
n-type materials such as perꢁuoroalkyl substituted C60-
ꢀused N-methylpyrrolidine-para-dodecyl phenyl derivative
(C60PC12F25) (LUMO = − 3.63 eV) (Chikamatsu et al.
2008), alkyl-substituted poly(benzoquinolinophenanthro
a
peak
b
peak
Eoxi oxidation peak potential (V). Ered reduction peak poten-
c
opt
tial (V). HOMO energy level calculated ꢀrom E
= −[E
HOMO
LUMO
g
d
+
peak
red
–
–
E
E
] eV. LUMO energy level calculated ꢀrom E
= −[E
LUMO
redox
e
(Fc/Fc )+5.1] eV. E = [HOMO ⋅ LUMO] eV.
g
Fig. 7 Cyclic voltammogram (ꢀull scan) oꢀ compounds 2 and 5 measured in anhydrous dichloromethane
1
3

Chemical Papers
linedione) (PNDI-2BocL) (LUMO = − 3.54 eV) (Durban
parent 1 the HOMO and LUMO spread over the entire mol-
ecule. However, in 2–6 the peripheral units were joined to
central phenazine core by C –C bond wherein HOMO is
et al. 2011), and N, N′-bis(1H,1H,2H,2H-perꢁuorodecyl)-
1
,4,5,8-naphthalene tetracarboxylic diimide (8–2-NTCDI)
1
2
(
LUMO= −3.77 eV) (Byung et al. 2010).
resided linearly on two oꢀ the peripheral segment and central
core through conjugation, whereas LUMO predominately
presents on central phenazine core witness’s occurrence oꢀ
characteristic HOMO–LUMO transitions in these molecules.
It is apparent ꢀrom electronic structures that the non-planar-
ity impairs the electronic coupling at some part oꢀ the mol-
ecule that leads to an absence oꢀ electron density over there.
In addition to these, poorly separated HOMO and LUMO
energy levels and small dipole moments in the molecules
prevail weak charge transꢀer transition between the donor
aryl groups and acceptor phenazine core (Chen et. al 2014).
The dipole moments obtained ꢀor 4 and 5 are large compared
Theoretical properties
To take a better insight into the impact oꢀ modulating donors
at the periphery oꢀ acceptor phenazine core on the HOMO
and LUMO energy levels oꢀ molecules, its electronic struc-
tures were computed using density ꢀunctional theory (DFT)
under B3LYP/6-311G basis set within a Gaussian 03 pro-
gram (Frisch et. al 2004). The optimized geometries and
theoretically calculated ꢀrontier molecular orbitals oꢀ 2 and
4
are presented in Fig. 8 (ꢀor other compounds, see SI Figure
S22–S33).
to other derivatives which are attributed to polar –OCH and
3
The HOMO and LUMO distribution in derivatives
–CN group on arylamine, respectively.
depend on its molecular design and are ꢀound to be aꢂected
due to molecular conꢀormation. It can be observed that in
The computationally calculated energies oꢀ the HOMO
and LUMO levels, HOMO–LUMO gap, vertical ionization
Fig. 8 Optimized structures and Correlation diagram showing Frontier molecular orbitals and energies oꢀ 2 and 4
1
3

Chemical Papers
Table 3 Computed Ionization potentials, electron aꢃnities, wavelengths, oscillator strengths, main vertical electronic transition in the gas phase,
orbital energies, and dipole moments oꢀ 1–6
Compound Ea (eV) Ip (eV) λmax
F
Assignments
EHOMO (eV) ELUMO (eV) Eg (eV) Dipole (debye)
(
nm)
1
2
3
4
5
6
7.93
6.97
6.81
6.66
7.71
7.14
1.86
1.62
1.61
1.43
2.31
1.92
397
84
422
07
443
27
444
22
419
08
428
12
0.1163 HOMO→LUMO (61.22%)
−6.71
−6.06
−5.92
−5.72
−6.73
−6.24
−3.14
−2.70
−2.70
−2.54
−3.35
−2.95
3.58
3.36
3.22
3.18
3.37
3.27
1.41
0.53
0.53
1.79
4.83
2.00
3
0.0012 HOMO–3→LUMO+1 (70.28%)
0.4919 HOMO→LUMO (68%)
4
0.1749 HOMO–1→LUMO (66%)
0.2609
0.1497 HOMO–1→LUMO (67%)
0.5985 HOMO→LUMO (69%)
0.1241 HOMO–1→LUMO (68%)
0.5621 HOMO→LUMO (67%)
0.2150 HOMO–1→LUMO (66%)
0.7388 HOMO→LUMO (68%)
0.1268 HOMO–1→LUMO (67%)
HOMO→LUMO (68%)
4
4
4
4
potential, electron aꢀꢀinity, and the ground state dipole
moment ꢀor all derivatives are given in Table 3. The
HOMO and LUMO energy oꢀ 2–6 is in the range oꢀ −5.72
to −6.73 eV and −2.54 to −3.35 eV, respectively. These
HOMO values are comparable with experimentally calcu-
lated energy levels to some extent, whereas LUMO values
show slight deviation with experimentally obtained data.
Substitution with diꢂerent peripheral donor units on parent
1
considerably tunes HOMO and LUMO energy level val-
ues. In which, an increase in π—conjugation in donors like
biphenyl, naphthyl in 2, 3, and strong EDG –OCH group in
3
4
leads to higher HOMO energy level values. Conversely,
the presence oꢀ EWG –CN group and quinoline is respon-
sible ꢀor lower LUMO values in 5 and 6. The computed
bandgap ꢀor 2–6 gets lowered as compared to parent 1 and is
in the range oꢀ 3.18–3.37 eV. The small bandgap (3.18 eV)
in 4 is assigned to strong electron-donating –OCH group
3
Fig. 9 TGA thermogram oꢀ 2–6 under nitrogen atmosphere at normal
on aryl segment.
pressure. Heating rate, 10 °C/min
The transition energies, oscillator strength, and assign-
ment ꢀor the most relevant singlet excited states in each oꢀ
the molecules are given in Table 3, and other assignments
are given in supporting inꢀormation. The frst vertical ioniza-
tion potential (IP) and the electron aꢃnity (EA) were calcu-
lated computationally as the diꢂerence in the total energies
oꢀ neutral and cationic/anionic species, respectively. There-
aꢀter, the optical properties were evaluated by TD–DFT in
the gas phase using 6-311G basis set (ꢀor simulated elec-
tronic absorption spectra oꢀ 1–6 in the gas phase, see SI
Figure S34). The transitions above 350 nm correspond to
charge transꢀer transitions in the dyes and have been aꢂected
by modulating peripheral donor segments in the molecule.
determined by the open capillary method. The TGA ther-
mogram oꢀ 2–6 has been obtained in a nitrogen atmos-
phere at normal pressure with heating rate, 10 °C/min,
and displayed in Fig. 9 (For 1, see SI Figure S35). The
slight increase in mass on the increasing temperature at
beginning oꢀ the TGA thermogram can be attributed to
the buoyancy eꢀꢀect in the TGA system. (Bottom 2008).
However, the TGA thermogram oꢀ 2‒6 revealed that
these dyes exhibit good thermal stability. The decompo-
sition temperature corresponds to 5% and 10% weight
losses are ꢀound in the range 222‒438 °C and 243‒452
°C respectively (Table 4). The order oꢀ thermal stability
in derivatives 2‒6 is 3 > 4 > 2 > 6 >5.
Thermal properties
The thermal stability oꢀ 1–6 was studied by thermo-
gravimetric analysis (TGA), and the melting point was
1
3

Chemical Papers
Table 4 Thermal properties oꢀ compounds 1–6
Compound
1
2
3
4
5
6
TGA
a
T5 (°C)
346
360
249
329
438
452
285
316
222
243
250
262
a
T10 (°C)
Conclusion
distilled using the standard procedures and handled in a
moisture-ꢀree atmosphere. Column chromatography was
carried out using SD-fne silica gel (60–120 mesh), eluting
with n-hexane and chloroꢀorm. The progress oꢀ the reaction
and the purity oꢀ the compound was checked by thin-layer
chromatography (TLC) on silica-gel-coated glass plates, in
which the spots were visualized with UV light (365 nm) and
in an iodine chamber.
In summary, fve C–C-coupled D–A-based phenazine deriv-
atives are synthesized and characterized. It is observed that
adduct 1 is non-emissive and electron-defcient, whereas
attachment oꢀ donor aryl moieties at periphery induces
emission in 2–4 derivatives. The absorption and emission
spectra were inꢁuenced by the nature oꢀ peripheral donor
aryl moieties and demonstrate the ꢀormation oꢀ charge-trans-
ꢀ
er complexes. The resulting luminogen shows weak D–A
Instrumentation and methods
interaction but characteristic emission in the blue region.
The optical band (2.62–3.08 eV) oꢀ synthesized dyes well
matches with reported blue-emitting organic semiconduc-
−
6
−1
UV–visible spectra were recorded in 10 mol L solu-
tion in a 1 cm path length quartz cuvette as well as the neat
solid flms on a SHIMADZU UV-2401PC instrument at
room temperature. The neat solid flm oꢀ compounds 2–6
was prepared by using a spin coater (Holmarc HO-TH-05)
tors. Further, solvent polarity plots viz. E
vs emission
T(30)
wavelength, Lippert–Mattaga and Weller’s models provide
the validation oꢀ charge transꢀer (CT) characteristics in a
designed D-A system. Aggregation studies oꢀ dyes 2 and 3
expose the ACQ in dye 2 and weak AIE in dye 3 wherein
the notable change in ꢁuorescence on the addition oꢀ water
to THF solution oꢀ dye 3 reveals its sensitivity ꢀor change
in medium with water. The FEG-SEM studies unveil the
nanoparticles oꢀ 3 that get ꢀormed at higher water ꢀraction
−
1
at 1000 rpm ꢀor 2 min∼6 mg mL oꢀ the sample in chlo-
roꢀorm. Quartz plates were used ꢀor neat solid flm studies.
The excitation and emission spectra were carried out on a
PerkinElmer LS 55 Fluorescence spectrophotometer. Cyclic
voltammetry studies were carried out on a computer-con-
trolled Palmsens3 potentiostat. Typically, a three-electrode
cell equipped with a glassy carbon working electrode, an
Ag/AgCl (non-aqueous) reꢀerence electrode, and platinum
(Pt) wire as the counter electrode was employed. The meas-
urements were carried at room temperature in anhydrous
dichloromethane with tetra-butyl ammonium hexaꢁuoro-
phosphate solution (0.1 M) as the supporting electrolyte with
(
ƒ = 80% in THF/water mixtures) are spherical in nature
w
with a mean diameter oꢀ 31–68 nm. Electrochemical inves-
tigation shows that electron-accepting property retains in the
derivatives. The HOMO and LUMO are in the range−6.38
to − 6.82 eV and − 3.67 to − 3.75 eV, respectively, and
ꢀ
ound to be comparable with reported electron-transporting
−
1
(
n-type) materials. DFT and TD-DFT studies veriꢀy weak
a scan rate oꢀ 100 mVs . The potential oꢀ the Ag/AgCl
reꢀerence electrode was calibrated by using a ꢀerrocene/
ꢀerrocenium redox couple, which has the known oxidation
potential oꢀ+5.1 eV. The thermogravimetric analysis (TGA)
was perꢀormed using a MetlerToledo instrument (TG)
D–A interaction in the molecules through poorly sepa-
rated HOMO and LUMO energy levels and small dipole
moments. Additionally, all the dyes possess good thermal
stability. From these results, we believe that the synthesized
dyes could be used as blue emitters and electron-transporting
1
13
under nitrogen atmosphere. H and C NMR spectra were
(
n-type) materials in optoelectronics.
recorded using CDCl on Varian 300 MHz Ultrashield spec-
3
trometer with tetramethylsilane (TMS) as an internal reꢀer-
ence at working ꢀrequency 300 and 75 MHz, respectively.
Fourier transꢀorm inꢀrared (FT–IR) spectra were recorded on
a PerkinElmer Frontier 91,579. Mass spectrometric meas-
urements were recorded using MALDI–TOF (Bruker), and
elemental analysis was carried out on EA Euro–elemental
analysis instrument. To confrm the ꢀormation oꢀ nanoparti-
cles in AIE studies, the sample oꢀ synthesized dye was sub-
jected to feld emission gun scanning electron microscopy
(JEOL JSM-7600F FEG–SEM).
Experimental section
Chemicals and materials
All the starting materials and reagents were purchased ꢀrom
commercial sources (Sigma-Aldrich and Alꢀa Aesar) and
were used without any ꢀurther treatment and purifcation
unless otherwise mentioned. The organic solvents were oꢀ
HPLC and spectroscopic grade and were dried and ꢀreshly
1
3

Chemical Papers
Synthesis procedures
calcd ꢀor C H N : C 91.27, H 4.92, N 3.80 ꢀound: C 91.18,
5
6
36
2
H 5.02, N 3.80.
Synthesis of 3,6,11‑tribromodibenzo[a,c]phenazine (1).
3
,6,11‑tri(naphthalen‑1‑yl)dibenzo[a,c]phenazine (3)
Compound 1 was prepared and obtained according to the
reported procedure (Shaikh et al. 2017, Xie et al 2020) as
mint green solid. Yield 1.20 g (93%); mp>250 °C. FT–IR,
Greenish solid, yield: 60 mg (48%); mp ˃250 °C. FT–IR
−
1
1
(KBr, ν
cm ): 3042, 2928, 1358, 1045, 760; H NMR
max
−
1
(
KBr, ν
cm ): 3070, 1587, 1358, 1054, 825; MALDI-
(300 MHz, CDCl ) δ 9.58–9.34 (m, 2H), 8.92–8.68 (m, 2H),
max
3
+
TOF: mass calcd ꢀor C H Br N [M ]: 517.01, ꢀound:
8.57 (d, J = 16.5 Hz, 1H), 8.44–8.31 (m, 1H), 8.25–7.91
2
0
9
3
2
1
3
5
1
18.87; elemental anal. calcd ꢀor C H Br N : C 46.46, H
(m, 5H), 7.86–7.32 (m, 19H); C NMR could not be
obtained due to poor solubility, MALDI-TOF: mass calcd
2
0
9
3
2
.75, Br 46.36, N 5.42. ꢀound: C 46.15, H 1.88, Br 46.47,
+
N 5.50.
ꢀor C H N [M ]: 658.79, ꢀound: 658.39; elemental anal.
5
0
30
2
calcd ꢀor C H N : C 91.16, H 4.59, N 4.25 ꢀound: C 91.07,
50
30
2
H 4.65, N 4.28.
General procedure ꢀor the synthesis oꢀ 2–6
3
,6,11‑tris(4‑methoxyphenyl)dibenzo[a,c]phenazine
Toluene (30 mL) and aqueous solution oꢀ K CO (2 M,
(4) Red solid, yield: 34 mg (30%); mp ˃250 °C. FT–IR
2
3
−
1
1
2
0 mL) were added to a ꢀlask containing a mixture
(KBr, ν
cm ): 3062, 2919, 1596, 1244, 817; H NMR
max
1
3
oꢀ compound 1 (0.1 g, 0.19 mmol), aryl-boronic acid
and C NMR could not be obtained due to poor yield and
+
(
(
0.57 mmol), Pd (dba) (20 mg, 0.02 mmol), and SPhos
solubility; MALDI-TOF: mass calcd ꢀor C H N O [M ]:
2
3
41 30
2
3
25 mg, 0.048 mmol). The reaction mixture was continu-
598.69 ꢀound: 598.24; elemental anal. calcd ꢀor C H N O
41 30 2 3:
ously stirred under a nitrogen atmosphere at 100 °C ꢀor
C 82.25, H 5.05, N 4.68 ꢀound: C 82.37, H 5.16, N 4.72.
1
6–24 h. The reaction mixture was cooled to room tem-
perature and extracted with chloroꢀorm (5 × 25 mL), and
the solution was then washed with water (5 × 25 mL). All
organic layers were combined and dried with anhydrous
Na SO and evaporated to obtain the dry crude product. To
4,4 ’, 4’’‑(dibenzo[a,c]phenazine‑3,6,11‑triyl)tribenzonitrile
(5) Green solid, yield: 54 mg (48%); mp 190 °C. FT–IR
−
1
1
(KBr, ν
cm ): 3051, 2919, 1358, 1026, 760; H NMR
max
(300 MHz, CDCl ) δ 9.45–9.33 (m, 2H), 8.93 (s, 1H), 8.55
2
4
3
get insight to obtain pure product by column chromatogra-
phy, the TLC oꢀ crude product and reactant was checked
beꢀore proceeding to separation with column chromatog-
raphy. Thereaꢀter, the slurry oꢀ crude product was made by
mixing it with chloroꢀorm and silica (60–120 mesh), where
the mixture was dried to aꢂord a ꢀree-ꢁowing slurry. Silica
(t, J=6.2 Hz, 2H), 8.47(s, 1H), 8.39–8.25 (m, 2H), 8.23
1
3
(d, J=4.2 Hz, 1H), 7.95–7.66 (m, 12H); C NMR could
not be obtained due to poor solubility; MALDI-TOF: mass
+
calcd ꢀor C H N [M ]: 583.64, ꢀound: 583.21; elemental
4
1
21
5
anal. calcd ꢀor C H N : C 84.37, H 3.63, N 12.00 ꢀound::
4
1
21
5
C 84.21, H 3.71, N 12.08.
(
60–120 mesh) column was prepared in 100% n-hexane,
and slurry oꢀ crude product was loaded through n-hexane
on the column. Then, the column was run with diꢂerent
ratios oꢀ n-hexane/chloroꢀorm to obtain purifed com-
pounds as green to dark red solids (Compound 2, 3, 4, 5,
and 6 were purifed by using n-hexane/chloroꢀorm with
ratio 80:20, 80:20, 60:40, 60:40, and 70:30, respectively).
3,6,11‑tri(quinolin‑3‑yl)dibenzo[a,c]phenazine
(6) Yel-
low solid, yield: 52 mg (45%); mp 195 °C. FT–IR (KBr,
−
1
1
ν
cm ): 3051, 2957, 1263, 1017, 760; H NMR
max
(300 MHz, CDCl ): δ 9.38 (d, J=7.6 Hz, 2H), 8.93–8.87
3
(m, 3H), 8.54 (d, J=7.8 Hz, 2H), 8.31 (dd, J=6.4, 3.5 Hz,
2H), 7.92–7.68 (m, 12H), 7.66–7.57 (m, 4H), 7.45–7.36 (m,
1
3
2
1
H); C NMR (75 MHz, CDCl δ 143.32, 142.44, 142.19,
3
32.05, 130.50, 130.29, 129.73, 129.46, 128.97, 128.39,
3,6,11‑tri([1,1’‑biphenyl]‑3‑yl)dibenzo[a,c]phenazine (2)
127.92, 126.27, 125.43, 122.90; MALDI-TOF: mass calcd
+
ꢀ
or C H N [M ]: 661.71 ꢀound: 662.03; elemental anal.
4
7
27
5
Greenish solid, yield: 70 mg (50%); mp ˃250 °C. FT–IR
calcd ꢀor C H N : C 85.30, H 4.11, N 10.58 ꢀound C
4
7
27
5
−
1
1
(
KBr, ν
cm ): 3058, 2923, 2852, 1350, 750, 693; H
85.11, H 4.27, N 10.62.
max
NMR (300 MHz, CDCl ) δ 9.37 (dd, J=4.5, 4.5 Hz, 2H),
3
8
.72 (s, 2H), 8.51 (s, 1H), 8.31 (d, J=8.9 Hz, 1H), 8.16–7.91
Preparation of nano‑aggregates
1
3
(
m, 6H), 8.16–7.91 (m, 24H); C NMR (75 MHz, CDCl ):
3
δ 142.16, 142.14, 142.09, 141.51, 141.06, 140.97, 140.40,
Stock THF solution oꢀ the dyes 2 and 3 with concentration
–
4
1
1
32.18, 129.51, 129.44, 128.90, 127.55, 127.35, 127.26,
10 M was prepared. Aliquots oꢀ stock solution were trans-
ꢀerred to a 5 mL volumetric ꢁask. Aꢀter dissolving the dye in
an appropriate amount oꢀ THF, water was added drop-wise
26.60, 126.49, 121.53; MALDI-TOF: mass calcd ꢀor
+
C H N [M ]: 736.90, ꢀound: 736.31; elemental anal.
5
6
36
2
1
3

Chemical Papers
–
5
under vigorous shaking to obtain a 10 M solution with diꢀ-
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d0se00687d
ꢀ
(
PL) measurement oꢀ the resultant solution was recorded.
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ian Inc, Wallingꢀord CT.
(
TD–DFT) calculations were perꢀormed using Gaussian 03
soꢀtware package using B3LYP as exchange–correlation
unctional at 6–311G basis set.
ꢀ
Supplementary Information The online version contains supplemen-
tary material available at https://doi.org/10.1007/s11696-021-01772-y.
Acknowledgements The authors are greatly thankꢀul to the Micro-
Analytical Laboratory, Department oꢀ Chemistry, the University oꢀ
Mumbai ꢀor providing Instrumental ꢀacilities. We sincerely thank the
Tata Institute oꢀ Fundamental Research (TIFR), Mumbai ꢀor provid-
ing MALDI-TOF and Sophisticated Analytical Instrument Facility,
IIT Bombay ꢀor providing FEG-SEM. The author DNK is grateꢀul to
DST–PURSE ꢀor JRF.
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Authors and Aꢀliations
1
1
1
Deepali N. Kanekar · Purav M. Badani · Rajesh M. Kamble
1
*
Rajesh M. Kamble
Department oꢀ Chemistry, University oꢀ Mumbai, Santacruz
kamblerm@chem.mu.ac.in
(E), Mumbai 400098, India
1
3