Rational Synthesis of Tetrahydrodibenzophenanthridine and Phenanthroimidazole as Efficient Blue Emitters and their Applications

Article abstract of DOI:10.1002/ejoc.201901711

Ten luminophores based on tetrahydrodibenzophenanthridine (THDP) and phenanthroimidazole (PI) were designed, synthesized and characterized for their thermal, electrochemical, electro-optical, charge-transporting characteristics and electroluminescent prop

Full text of DOI:10.1002/ejoc.201901711

A Journal of
Accepted Article
Title: Rational synthesis of tetrahydrodibenzophenanthridine
and phenanthroimidazole as efficient blue emitters and its
applications
Authors: Manojkumar Dhanthala Thiyagarajan, Umamahesh Balijapalli,
Sohrab Nasiri, Dmytro Volyniuk, Jurate Simokaitienec,
Madhvesh Pathak, Sathiyanarayanan Kulathu Iyer, and
Juozas Vidas Gražulevičius
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the VoR from the journal website shown below when it is published
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201901711
Link to VoR: http://dx.doi.org/10.1002/ejoc.201901711
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10.1002/ejoc.201901711
European Journal of Organic Chemistry
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Rational synthesis of tetrahydrodibenzophenanthridine and
phenanthroimidazole as efficient blue emitters and its
applications
Mr. Manojkumar Dhanthala Thiyagarajan a, Dr. Umamahesh Balijapalli a, b, Mr. Sohrab Nasiri c, Dr.
Dmytro Volyniuk c, Dr. Jurate Simokaitienec c, Prof. Madhvesh Pathak *a, Prof. Sathiyanarayanan
Kulathu Iyer *a and Prof. Juozas Vidas Gražulevičius *c
Abstract:
Ten
luminophores
based
on
can be done by two distinct methods, namely wet and dry
processes. Typically, dry-process is used to realize high efficiency
OLEDs with high-quality light.[6-8] Shortcomings such as inefficient
use of materials, high energy consumption and poor scalability
are major issues in cost-effective, mass-production.
tetrahydrodibenzophenanthridine (THDP) and phenanthroimidazole
(PI) were designed, synthesized and characterized for their thermal,
electrochemical, electro-optical, charge-transporting characteristics
and electroluminescent properties. The blue luminophores exhibited
high photoluminescence quantum yields of 66-93% in toluene
solutions and of 5-59% in solid films. The highest values were
observed for the derivative of THDP and PI containing methoxy group.
The compounds showed close values of ionization potentials (5.74-
6.11 eV) and electron affinities (2.71-3.06 eV). The selected
compounds were tested in electroluminescent devices for the
preparation of non-doped light-emitting layers. The best device
fabricated using derivative of THDP and PI with methoxy groups
showed blue electroluminescence with brightness of 10000 cd/m2 at
high applied voltages. We performed DFT calculations, and observed
lowest singlet-triplet gap (∆EST) values of 0.33 and 0.03 eV, oscillator
strength (f) values of 0.034 and 0.008 for CN and NO2 derivatives.
Interestingly, we observed that compounds 3g and 3i showed HOMO
and LUMO levels of almost similar energy gap (Eg) of 3.60 eV and we
observed deeper HOMO values of -5.30, -5.33 eV and LUMO values
of -1.94, -2.77 eV.
In contrast, some of the aforementioned approaches can be
adopted in wet-process to fabricate high-quality light OLED
devices, but with comparatively low efficiency. Nevertheless, wet-
process is deemed far superior in enabling simple fabrication,
large area-size and roll-to-roll production, and consequently more
cost-effective. However, energetic doping often requires minute
control of doping concentration and inescapably increases
manufacturing cost and this type of phase separation in the
dopant-host system can make energy transfer ineffective. Many
recent researchers have reported a high efficiency of blue
fluorescent materials.[9-12] Some of them offer deep-blue emission
with CIEy<0.10.[13] Recently, Benzimidazole-based materials that
possess different functional chromophores have been
demonstrated as deep-blue-light emitters.[14] However, these
materials have deep HOMO, thereby leading to larger hole-
injection barriers at the hole-transporter emitter junctions, and
thus they require higher operation voltages and provide lower
efficiencies.[15-16] In fact, deep-blue OLEDs with high efficiency,
good color stability, and low working voltage are rare.[17-20]
Introduction
Tetrahydrodibenzophenanthridine (THDP) is
a
well-known
fluorophore with exceptional photophysical properties, used as
intermediate for the construction of organometallics and also
utilized as a ratiometric fluorescence sensor for the detection of
aniline.[21] On the other hand, 1,3,5-tris(N-phenylbenzimidazol-2-
yl)benzene (TPBi) was widely used as an electron-injection and
hole-blocking material in OLEDs, However, due to localization of
its emission in the ultraviolet spectral region (368 nm), TPBi can
not be used as an emitter. Phenanthro[9,10-d]imidazole (PI)
containing imidazole unit exhibits excellent thermal stability,
highly efficient photoluminescence (PL) quantum yields and
balanced charge carrier injection properties which make
derivatives of PI promising candidates for OLEDs.[22] This
information inspired us to develop new derivatives of THDP and
PI as blue materials by a facile synthetic processes followed by
systematic studies of their thermal, photophysical, and charge
injection properties. In addition, postfunctionalization of
derivatives of THDP and PI was performed by functional groups
such as NO2, CN, methoxy, methyl, and by halogens.
Organic light-emitting diodes (OLEDs) have drawn massive
attention due to their increasing applications in flat-panel displays
and lighting devices.[1] OLEDs can be driven at low voltages to
produce high brightness, wide viewing angles, fast response, low
power consumption light-weight,[2] industrial and professional
displays and micro-display products have already been
developed.Researchers
have
reported
deep-blue
phosphorescent materials.[3,4] Phosphorescent OLEDs can
theoretically achieve 100% internal quantum efficiency. However,
blue phosphorescent OLEDs have short lifetime and sharp
efficiency roll-off at high brightness. [5] The fabrication of OLEDs
[a]
Mr. Manojkumar Dhanthala Thiyagarajana, Prof. Madhvesh Pathak, Prof.
Sathiyanarayanan Kulathu Iyer, Department of Chemistry, School of Advanced
Sciences, Vellore Institute of Technology, Vellore-632014, Tamilnadu, India. E-mail;
sathiya_kuna@hotmail.com and madhveshpathak@vit.ac.in
https://www.sites.google.com/site/sathiyanarayananresearchgroup/home?authuser=0
Dr. Umamahesh Balijapallia, Centre for Organic Photonics and Electronics Research
(OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan.
http://www.cstf.kyushu-u.ac.jp/~adachilab/lab/
[b]
[c]
Mr. Sohrab Nasiric, Dr. Dmytro Volyniukc, Dr. Jurate Simokaitienecc, Prof. Juozas
Vidas Gražulevičius Kaunas University of Technology, Department of Polymer
Chemistry and Technology, Radvilenu pl.19, LT 50254, Kaunas, Lithunania, E-mail;
juozas.grazulevicius@ktu.it
In this work, we used the donor-π-acceptor approach to design
new molecules with PI core as the acceptor for its good electron-
transporting mobility and THDP as the donor for good hole
transport mobility and for connecting them with different linkers.
https://fct.ktu.edu/department-of-polymer-chemistry-and-technology/
Supporting information for this article is given via a link at the end of the document.
[23-26]
New THDP and PI derivative containing methoxy group
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10.1002/ejoc.201901711
European Journal of Organic Chemistry
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showed the highest photoluminescence quantum yields in both Photophysical properties
toluene solutions (93 %) and in solid state (59 %). The best device
performance was observed using non-doped light-emitting layer
of this compound.
To investigate the effect of the substitution pattern on
photophysical properties of the THDPs and PI derivatives,
absorption and photoluminescent (PL) spectra of their solutions
and solid films were recorded (Figure 1a-d and Figure S1). Low-
energy bands of absorption spectra of toluene solutions of all
derivatives were characterized by maxima at 346-361 nm and
low-intensity shoulder at 365-375nm. These absorption bands
can be mainly attributed to absorption of PI moiety, since the
lowest energy band is situated at the same region (with maximum
at 364 nm) and is red-shifted in comparison to the lowest energy
band (with maximum at 318 nm) of BTHDPs (Table 1).[29-33] Small
blue-shifts of the maxima of the lowest energy bands of
compounds 3a-j relative to that of PI is, apparently, the result of
superposition of absorption spectra of both donating and
accepting units. Additional red-shifted energy bands (shoulders)
that indicate intramolecular charge transfer (ICT) transitions in
ground states between donor and acceptor units were practically
not observed because of the presence of diphenyl spacers
between THDP and PI moieties. As a result, similar optical energy
band gaps (Egopt) were obtained for the studied compounds (Table
1). Slight differences in the position of the lowest absorption
bands were observed for the toluene solutions of derivatives 3a-j
due to their post-functionalization’s by different moieties inducing
different steric and polar effects, which affected electron
delocalization. A similar absorption behavior of the derivatives 3a-
j was also observed more in polar solvents than in toluene,
revealing their weak solvatochromic effects in ground states.
Absorption spectra of solid films of 3a-j practically reconstituted
the corresponding spectra which were only slightly red-shifted
due to the aggregation effects of the solutions (Figure 1b).
Intensive, deep-blue fluorescence with high photoluminescence
quantum yield (PLQY) was observe for toluene solutions of
compounds 3a-j (Table 1). The highest PLQY value of 93 % was
recorded for toluene solution of compound 3f containing metoxy
substituent. PL decays of the toluene solutions were agreed well
with the mono-exponential law (Figure 1c and 2). Close to
nanosecond, life times of fluorescence were observe for all the
solutions, displaying weak effect of the substitution pattern (Table
1). For adequate description of PL decay curves of the films of
compounds, double or triple exponentials fits were required. The
reasons of different PL decays of the films from those solutions
could be due to aggregation induced quenching and/or excimer
formation. Clear effect of substitution pattern on PL decays of the
films of 3a-j was observed (Figure 1c, 2 and Table 1). Different
shapes of PL decays of the films 3a-j may partly be related to non-
radiative losses in solid-state. Indeed, much lower PLQY values
of solid samples of 3a-j were obtain in a comparison to those of
their toluene solutions (Table 1). Compound 3f, containing
methoxy group, demonstrated relatively high PLQY of 59% in
solid-state. It was higher than that of compound 3a, which did not
have any substituent at phenyl group linked to PI moiety. High
PLQY of solid sample of 3f can be related to restriction of excimer
formation, which may occur between planar moieties, as it was
shown elsewhere. [34]
Synthesis and Characterization
THDP was easily prepared by the one-pot condensation reaction
of substituted aldehydes, ammonium acetate and 2-tetralone with
good yields.[27] 5-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)phenyl)-7,8,13,14-tetrahydrodi benzo[a,i] phenanthridine
1
(BTHDP) which is a key intermediate (its chemical structure
shown in Scheme 1) was synthesized in good yield of 65%
according to the previously reported procedure (see the
experimental section for the details).[28] The reaction of 9, 10-
phenanthrenequinone, p-bromobenzaldehyde with substituted
aniline derivatives in the presence of ammonium acetate, and
acetic acid gave substituted bromophenyl phenanthroimidazoles
(BrPI) as yellow solids with up to 90% yields (see supporting
information).
R
O
O
B
Br
Pd(PPh3)4
Cs2CO3
N
N
R
N
N
N
N
Dioxane:H2O (4:1)
80oC, 24h
3f : R = 4-MeO, 67%
3g : R = 4-CN, 66%
3h : R = 3,5-MeO, 60%
3i : R = 4-NO2, 68%
3j : R = 2-pyridine, 65%
3a : R = H, 78%
3b : R = 4-Me, 74%
3c : R = 4-F, 69%
3d : R = 4-Cl, 64%
3e : R = 3,5-Me, 72%
2a-j
1
Scheme 1: Synthesis of 5-(4'-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)-
[1,1'-biphenyl ]-4-yl)-7,8,13,14-tetrahydrodibenzo[a,i]phenanthridine and its
derivatives.
In the final step, we used palladium-catalyzed Suzuki coupling to
couple BTHDP with BrPI derivatives to obtain THDP-PI bipolar
fluorophores (3a-3j) as shown in Scheme 1. The optimized
reaction conditions were established by the screening of catalyst,
solvent, base, temperature. TThe details were given in Table S1
in supporting information. It found out that 10 mol% Pd(PPh3)4 and
2 eq of Cs2CO3 in dioxane/H2O (4:1) allowed to obtain compound
3a in 78% yield (Table S1). Functional groups such as NO2, CN,
methoxy, methyl, and halogens tolerated the reaction conditions
and the coupling smoothly proceeded to produce the desired
compounds in good yields. All the compounds were freely soluble
in common organic solvents and were purified by column
chromatography using a mixture of ethylacetate/chloroform /n-
hexane as the eluent. Further, the purity was improved by
consecutive crystallization steps and the structures were
ascertained by FTIR, NMR, and mass spectrometry analysis (see
section 1, supporting information).
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Table 1. Photophysical parameters of the solutions of compounds 3a-j in toluene and solid films.
FWHM,
nm
CIE1931,
(x, y)
Slopea,
cm-1
λFmax
, nm
max
abs
Egopt, eV
, ns
PLQY, %
, nm
τ
λ
Compounds
Toluene/film
417, 435/
463
0.92/
0.13, 7.33
(0.154, 0.059)/
(0.202, 0.249)
3a
3b
3c
3d
3e
3f
348/352
346/351
347/355
345/355
348/352
349/351
352/362
349/355
357/362
355/367
3.03/2.76
93/27
67/11
87/32
66/8
77/125
67/126
69/128
67/131
68/135
66/137
68/91
7513
6931
2958
2633
3846
8240
3893
6229
8511
8146
417,434/
480
0.96/
0.68, 4.43
(0.156, 0.063)/
(0.204, 0.176)
3.01/2.79
415,434/
465
0.95/
0.21, 2.04, 8.12
(0.156, 0.056)/
(0.202, 0.249)
3.05/2.79
3.02/2.78
3.01/2.78
3.02/2.77
3.02/2.80
3.01/2.78
3.01/2.79
2.96/2.76
416,434/
502
1.02/
0.09, 1.72, 7.49
(0.157, 0.063)/
(0.236, 0.349)
418,435/
503
1.02/
0.11, 1.90, 7.89
(0.157, 0.065)/
(0.230, 0.335)
75/12
93/59
73/16
88/12
72/5
418,434/
480
0.93/
0.13, 1.56, 8.27
(0.155, 0.059)/
(0.214, 0.275)
417,434/
455
1.05/
0.06, 1.51, 9.74
(0.156, 0.062)/
(0.173, 0.179)
3g
3h
3i
417,432/
463
0.89/
0.55, 3.08, 10.6
(0.155, 0.065)/
(0.186, 0.222)
63/106
66/98
416,434/
469
0.95/
0.05, 1.03, 6.37
(0.155, 0.059)/
(0.179, 0.233)
418,434/
471
0.95/
0.03, 1.63, 9.19
(0.156, 0.060)/
(0.187, 0.245)
3j
74/6
64/105
Absorbance and emission, photoluminescence quantum yield (PLQY), full width at half maximum (FWHM), life time decay (τ), color coordinates (CIE 1931)
Vibronically structured PL spectra were recorded for the toluene
solution of the compounds (Figure 1a). These PL spectra
corresponded to pure deep-blue color with CIE1931 color
coordinates of (x<0.16, y<0.07) and full width at half maximum
(FWHM) < 77 nm (Table 1). Interestingly, FWHM of toluene
solutions of substituted compounds 3b-j was lower in comparison
to FWHM of 77 nm observed for the solution of non-substituted
compound 3a. The shapes of PL spectra were similar to the shape
of PL spectrum of DMF solution of PI.[35] PL spectra of the
solutions of 3a-j in toluene were red-shifted in comparison to PL
spectrum of the solution of PI. Further, red-shift of emission band
of compounds 3a-j was observed for the solution in chloroform,
THF, and acetone, owing to an increase in the polarity of the
solvents (Figure S2).
emission behavior, the dependence of their Stokes shifts versus
orientation polarizability of the chosen solvents (∆f) were linearly
fitted (Figure 1d). The different slopes (ranging from 2633 to 8511
cm-1) of these linear dependencies demonstrated differences in
dipole moments of excited singlet states of compounds 3a-j
according to the Lippert-Mataga law (Table 1).[36] Different
electron-donating or electron-accepting substituents of phenyl
group attached to PI moiety resulted in slightly different ICT
behavior of compounds 3a-j. Because of relatively low Lippert-
Mataga slopes for compounds 3a-j, some contribution of
recombination of locally-exited states to their emission is possible.
Non-structured nature of PL spectra of THF solutions of
compounds 3a-j at 77 K also suggests ICT emission (Figure 2).
At 77 K, phosphorescence was not detect apparently due to the
presence of bulky BTHDP unit. Broadening of PL spectra of the
films of 3a-j corresponds to some loss in deep-blue color purity in
comparison to that of toluene solutions (Figure 1b). FWHM lower
than 137 nm and CIE 1931 color coordinates of (x<0.16, y<0.07)
were obtained for PL of 3a-j in solid-state (Table 2). Nevertheless,
more than twice the higher PLQY of compound 3f containing
appropriate substituent in comparison to PLQY of non-substituted
counterpart 3a demonstrated efficiency of post-functionalization
in increase of potential for OLED applications.
As a result, different variations of Stokes shifts (∆υ=υabs-υem
)
displaying positive solvatofluorochromism and consistently
proving CT character of their emission (Table 1) were obtained for
the studied compounds. Non-structured PL spectra of the polar
chloroform, THF, and acetone solutions of compounds 3a-j
support the presumption that emission is a result of recombination
of CT exited states. To investigate the effect of the substitution
pattern of the derivatives THDP and PI derivatives on their
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Toluene solution
Solid Films
346-361 nm 417, 435 nm
352-369 nm
3a
3b
3c
3d
3e
3f
3g
3h
3i
455 - 503 nm
3a
3b
3c
3d
3e
3f
3g
3h
3i
1.0
1.0
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
3j
3j
300
350
400
450
500
550
600
650
300
400
500
600
700
800
Wavelength, nm
Wavelength, nm
a
b
7500
7000
6500
6000
5500
5000
4500
4000
3500
3a
10000
1000
100
3a
3b
3c
3d
3e
3f
3g
3h
3i
Toluene
Instrument Response
Fitting
3j
τ
= 0.92
1
10
2
χ
= 1.119
1
40
50
60
70
80
10000
Film
τ
= 0.13
1000
100
10
1
τ
= 7.33
2
2
χ
= 1.001
0.00
0.05
0.10
0.15
0.20
0.25
0.30
1
∆f
40
50
60
70
80
Time, ns
c
d
Figure 1 Absorption (dashed lines), and PL spectra (solid lines) of the solutions of compounds 3a-j in toluene (a) and of solid-state samples (b); PL decays of
toluene solution and solid film of compound 3a (c) and Lippert-Mataga plots displaying correlation between orientation polarizability of the solvent (∆f) and the
Stokes shifts (∆υ=υabs-υem) for compounds 3a-j (d)
Tg values can apparently be explained by relatively high molecular
weights and the rigid structures of the compounds. Small
differences in Tg values of compounds 3a-j can be attributed
either to their different molecular weights or to different
intermolecular interactions in solid states determined by different
Thermal, electrochemical and photoelectrical
characterization
substituents of PI moiety.
Most of the synthesized compounds, except 3i, were obtained
after purification as crystalline or semi-crystalline substances, as
confirmed by differential scanning calorimetry (DSC)
measurements. Their melting temperatures (Tm) ranged from 240
to 379 ºC. All the compounds were found to be capable of glass
formation. They showed relatively high glass transition
temperatures (Tg) of 176-205 ºC (Figure S6, Table 2). Such high
To estimate energy levels of compounds 3a-j, at the preliminary
stage, cyclic voltammograms (CV) of their solutions were
recorded (Figure 2a). The reversible oxidations and reductions
were observed, which highlighted their good electrochemical
stability of the compounds. Since all the studied compounds
contain THDP and PI moieties, the similar values of oxidation and
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10.1002/ejoc.201901711
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from the low-energy edge of absorption spectra of vacuum-
deposited films of 3a-j (Figure 3b, Table 2). Showing the similar
trends, IpPES and EAPES values of compounds 3a-j were slightly
Table 2 Thermal, electrochemical, electro optical and charge-transporting
characteristics of compounds 3a-j
CV
different from the corresponding IpCV and EA values (Table 2).
PE
IpCV#/IpPE
eV
,
EACV@/EA
eV
,
µh,a
Compounds
The values of IpPES and EAPES of compounds 3a-j were in good
agreement with the corresponding energy levels of functional
materials of OLEDs and efficient charge injection from the
electrodes can be predicted.
Tg, ºC
Tm, ºC
cm2/Vs
3a
3b
3c
3d
3e
3f
185
179
184
176
189
197
207
176
205
198
348
341
379
362
324
373
337
286
-
6/5.74
2.94/2.71
3.01/2.89
3.02/3.06
2.99/2.9
2.97/2.8
3/2.9
5.8·10-6
5.98/5.90
6.05/6.11
6.04/5.92
6.02/5.81
6/5.92
-
9·10-6
-
-
Charge-transporting properties
2.4·10-6
Owing to donor-acceptor molecular structures of the studied PI
and phenanthridine derivatives, we expected bipolar charge-
transporting properties. Such expectations were partly grounded
on the previously published phenanthridine/phenanthroimidazole
based compounds which showed relatively good hole or electron-
transporting properties.[37-38] To verify these expectations, time-of-
flight (TOF) technique was used for testing diode-like samples
with the structure of ITO/vacuum-deposited film/aluminum.
Unsubstituted compound 3a showed hole mobility of 1.3X10-4
cm2/V at electric fields higher than 106 V/cm (Figure 3). Post
functionalized compounds 3c, 3f and 3h showed hole motilities
similar to those of compound 3a at the same electric field. This
result indicated the absence of significant effects of post
functionalization on hole mobility’s of the studied derivatives. The
tested compounds were characterized by dispersive hole
transport, as was evident from the shapes of their photocurrent
transients (Figure S7). It was not possible to obtain transit times
(required for calculations of charge mobility) from photocurrent
transients for the other compounds, apparently due to the strong
charge-transport dispersing which is typical for good emitters.[39]
For the same reasons, transit times for electrons were also not
detected in the corresponding photocurrent transients.
3g
3h
3i
5.94/5.88
6.08/5.99
5.91/5.77
5.96/5.75
3.01/2.86
2.91/2.98
2.84/2.76
2.88/2.79
-
3.7·10-6
-
-
3j
240
#IPCV = 4.8+Eoxonset; @EACV = 4.8 - Eredonset; a taken at electric field of 6.4·105
V/cm.
reduction potentials were obtained. Small differences were
determined by the different substituents with weak electron-
accepting or electron-donating abilities attached to PI moiety
(Figure 2a). Oxidation of THDP moiety and reduction of PI moiety
were responsible for observed oxidation and reduction peaks of
compounds 3a-j. Ionization potential (IpCV) and electron affinity
(EACV) values estimated from CV measurements were obtain in
the ranges of 5.91-6.05 and 2.97-3.07 eV, respectively (Table 2).
CV
Since IpCV and EA energy levels are not directly related to the
solid layers of organic semiconductors, vacuum-deposited films
of 3a-j were additionally tested by electron photoemission
spectrometry in air (PES). The values of ionization potentials
(IpPES) for 3a-j in the condensed phase were estimate from the
corresponding photoelectron emission spectra extrapolating their
linear parts to zero of the ordinate axes (Figure 2b, Table 2).
Figure 3 Electric field dependences of the hole mobility in vacuum-deposited
film of compounds 3a, 3c, 3f and 3h
Electroluminescence
Figure 2 (a) Cyclic voltammograms of the solutions and (b) photoelectron
emission spectra of vacuum-deposited films of compounds 3a-j
Taking into account that compounds 3a, 3c, 3f and 3h are
characterized by relatively high PLQYs in solid-state and that they
are capable of transporting charges, electroluminescent
properties of the non-doped light-emitting layers of these selected
Meanwhile, electron affinities (EAPES) were calculate using the
equation EA= IPPES-Eg, where Eg is optical band-gap energy obtain
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European Journal of Organic Chemistry
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the film of 3a. In addition, differences between charge-injection
and charge-transporting properties of compounds 3a, 3c, 3f and
3h should also play important roles. The differences between
current density versus applied voltages characteristics were
observed for the studied devices (Figure 4c). Slightly different
turn-on voltages (Von= 4.9-5.4V) were obtained for the fabricated
devices (Table 3). For the device based on 3f, the film of which
showed PLQY of 59%, maximum EQE was two times lower than
its theoretical maximum (4.4%) estimated according to the well-
known relationship ηext = (γ × ηST × PLQY) × ηout using the charge
balance factor γ= 1 and the fraction of radiative excitons ηST = 0.25
for simple fluorescent emitters.[41] Therefore, further improvement
of EQE of device based on 3f can be expected. Nevertheless, the
performed electroluminescent investigations not only testify the
potential of the derivatives of THDP and PI in blue fluorescent
OLEDs, but also demonstrate the requirements of their
modifications through smart molecule design.
compounds were further tested in OLEDs with the structure
ITO/MoO3(1 nm)/NPB (30 nm)/3a, 3c, 3f or 3h (18 nm)/BPhen (33
nm)/LiF(0.5 nm)/Al. The layers of molybdenum trioxide (MoO3)
and lithium fluoride (LiF) were used as hole- and electron-injection
layers, and the layers of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-
biphenyl)-4,4′-diamine (NPB) and bathophenanthroline (BPhen)
were employed as hole- and electron-transporting layers,
respectively. As are result, energy barriers which might prevent
charge-injection into the light-emitting layers were absent in the
designed OLED structures (Figure 4a). In addition, the layers of
NPB and BPhen acted as electron- and hole-blocking layers due
to the LUMO-LUMO energy barrier between NPB and light-
emitting layers and the HOMO-HOMO energy barrier between
BPhen and light-emitting layers, respectively (Figure 4a). Thus,
recombination of charge pairs was anticipated within the light-
emitting layers of 3a, 3c, 3f or 3h. This expectation was in good
agreement with EL spectra of OLEDs based on 3a, 3c, 3f or 3h
(Figure 4b). The similar EL spectra with the intensity maxima at
474 nm were observed for all the fabricated devices. Stable EL
spectra under different electrical excitations were observed for the
devices, showing that the recombination zone was not shifted to
the charge-transporting layers under high electric fields partly due
to the good charge-blocking properties of NPB and BPhen (Figure
S6). EL spectra of devices 3a, 3c, 3f and 3h, being only slightly
different due to the different excitations used, i.e. optical and
electrical (Figure 1b, 4b), were in good agreement with PL spectra
of the corresponding films. CIE coordinates of the fabricated
devices corresponded with blue color (Figure S9, Table 3).
474 nm
3a
3c
1.0
3f
3h
2.40
0.8
2.71
2.90
2.9
2.98
5.99
LiF/AL
2.90
3.06
0.6
0.4
0.2
0.0
4.70
ITO
5.25
MoO
3
5.40
5.74
5.92
6.11
300 350 400 450 500 550 600 650 700 750 800
6.41
Wavelength, nm
a
b
10000
1000
100
450
400
350
300
250
200
150
100
50
3a
3c
3f
1
By tenfold increase in maximum brightness was observed for the
device, based on compound 3f containing OCH3 group in
comparison to that of device based on non-substituted emitter 3a
(Figure 4c). To understand why tenfold increase in maximum
brightness was observed for the device, based on compound 3f
containing methoxy group in comparison to that of device based
on non-substituted emitter 3a (Figure 4c), we plotted brightness
versus current density for the fabricated devices (Figure S10).
These dependences were well linearly fitted with the slope of 1 for
all the devices at low brightness demonstrating that their
3h
0.1
3a
3c
3f
3h
10
0.01
0
10
100
1000
10000
3
4
5
6
8
9
10
Voltage7(V)
Brightness (cd/m2)
c
d
Figure 4 Equilibrium energy diagram (a), EL spectra recorded at 7 V (b),
characteristics of current density and brightness versus applied voltages (c) and
dependences of EQEs versus brightness (d) of OLEDs. The inset is photo of
device 3f
electroluminescence
resulted
from
singlet
exciton
recombination.[40] In case of device f, the liner dependence of
brightness versus current density was observed at high current
density (Figure R1). This observation can be explained by the
perfect charge balance and/or negligible quenching of excitons at
broad range of electric fields in light emitting layer 3f. In contrast,
brightness of device a based on light-emitting layer 3a is
apparently limited by charge disbalance and/or exciton quenching
Theoretical Calculations
To estimate the differences between the geometric and optical
properties, quantum-chemical calculations were performed by
density functional theory (DFT) and time-dependent density
functional theory (TD-DFT) at the B3LYP/6-31G(d) level. The
calculated highest occupied molecular orbital (HOMO), lowest
unoccupied molecular orbital (LUMO), oscillator strength (f),
excited state energies and DEST are depicted in Figure S1 and
Table S2. The HOMO was mainly localized in PI units and
extended to phenyl parts of BTHDP core, there by suggesting that
PI acts as an acceptor. The LUMO was fully occupied on the
BTHDP donor unit and partially extended to the imidazole parts of
PI units, which suggested that the nature of the substitution could
also influence the optical properties.
at high electric fields (Figure S10).
In contrast to high roll-off efficiency of blue phosphorescent
OLEDs which suffered from formation of “hot excitons” due to the
presence of long-lived triplet excitons,[41] the fabricated blue
fluorescent device 3f showed low roll-off efficiency (Figure 4d). Its
external quantum efficiency (EQE) at very high brightness (L) of
10000 cd/m2 for blue OLEDs exhibited a slight drop in comparison
to its maximum EQE of 1.6% (Figure 4d). Better OLED
performances of devices based on 3c and 3f, in comparison with
that of the device based on 3a, were mainly related to higher
PLQY values of the films of 3c and 3f in comparison with that of
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10.1002/ejoc.201901711
European Journal of Organic Chemistry
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Table 3 Fabricated OLED device for 3a, 3c, 3f and 3h
For example, a slightly distinct trend was observed in 3g and 3i;
LUMO was fully localized only on N-phenyl parts of PI core owing
to the strong CN and NO2 acceptors at the para position. Due to
this, the HOMO was completely isolated and widely distributed to
PI, and the THDP core resulted in a small overlap of HOMO and
LUMO. This led to a small calculate lowest singlet-triplet gap
(∆EST) values of 0.33 and 0.03 eV, oscillator strength (f) values of
0.034 and 0.008 for 3g and 3i respectively. Hence, the increased
charge transfer (CT) character with red-shifted properties can be
observed. While the other emitters displayed almost similar
singlet and triplet energies, large ∆EST and increased f, with
completely overlapped HOMO and LUMO levels, suggest a
probable increase in PLQYs. Furthermore, the calculated HOMO
levels were in the range of 5.03-5.18 eV, while the LUMO levels
were in the range of 1.42-1.50 eV, which gave almost similar
energy gap (Eg) of 3.60 eV. Deeper HOMO values of -5.30, -5.33
eV and LUMO values of -1.94, -2.77 eV were observed for 3g and
3i respectively due to the acceptor's strength of CN and NO2
functionalities. The calculated optical parameters are tabulate in
Table S2.
L at
9 V
(cd/
m2)
PE
max
(lm/
W)
EQ
Em
ax
CIE1931
CEma
x
(cd/A)
Von
(V)
Lmax
coordinates
(x, y) at
10V
Device
(cd/m2)
(%)
3a:
ITO/MoO3/
NPB/3a/TP
Bi/LiF/Al
(0.194,
0.256)
5.2
5.1
4.9
5.4
1100
4100
11300
4100
900
0.8
1.2
1.6
0.6
1.9
1.9
1.9
0.7
0.8
1.2
1.6
0.6
3c:
ITO/MoO3/
NPB/3c/TP
Bi/LiF/Al
(0.185,
0.244)
2100
8300
2200
3f:
ITO/MoO3/
NPB/3f/TP
Bi/LiF/Al
(0.179,
0.246)
3h:
ITO/MoO3/
NPB/3h/TP
Bi/LiF/Al
(0.201,
0.267)
PEmax and CEmax are maximum power and current efficiencies, respectively
Conclusions
Ten
new
fluorescent
derivatives
of
GC Mate II GC-mass spectrometer. FTIR spectra of the
synthesized organic compounds were recorded using a Jasco-
4100 spectrometer instrument. Ultraviolet−visible spectra were
tetrahydrodibenzophenanthridine and phenanthroimidazole were
designed, synthesized and characterized as emitters for blue
organic light-emitting diodes. Toluene solutions of the compounds
exhibited a high photoluminescence quantum yield up to 93 %.
For the films, photoluminescence quantum yields up to 59% were
observed. The best blue OLED exhibited brightness exceeding
10000 cd/m2 and a relatively low roll-off efficiency. The best
photoluminescence and electroluminescence performances were
observed for the compound containing methoxy substituents. We
performed DFT calculations and observed the lowest singlet-
triplet gap (∆EST) values of 0.33 and 0.03 eV, oscillator strength
(f) values of 0.034 and 0.008 for CN and NO2 derivatives.
Interestingly, the compound 3g and 3i values were HOMO levels,
and they were in the range of 5.03-5.18 eV, while the LUMO levels
were in the range of 1.42-1.50 eV, which offered an almost similar
energy gap Eg of 3.60 eV. The deeper HOMO values were found
to be -5.30, -5.33 eV while the LUMO values were -1.94, -2.77 eV.
recorded using
a
Hitachi U-2910 spectrophotometer.
Fluorescence spectra in solution and solid state were measured
using a Hitachi F7000 fluorescence spectrometer.
Photoluminescence (PL) spectra of 10−5 M solutions and of solid
films of the compounds were recorded using Edinburgh
Instrument FLS980 Fluorescence Spectrometer. For recording
the UV/VIS and PL spectra, thin solid films were prepared by the
spin-coating technique utilizing SPS-Europe Spin150 Spin
processor using 1 mg/mL solutions of the compounds in
chloroform on the pre-cleaned quartz substrates. The PL spectra
were recorded at a low temperature (77 K). Fluorescence
quantum yields (ΦF1) of the solutions and of the solid films were
estimated using an integrated sphere. Edinburgh Instruments
FLS980 spectrometer with Pico Quant LDH-D-C-375 laser
(wavelength 374 nm) as the excitation source was utilized for
photoluminescence decay curves. Differential scanning
calorimetry (DSC) measurements were carried out in a nitrogen
atmosphere with a DSC TA Instruments Q2000 thermal analyser
at a heating rate of 10 °C/min. The sample (approximately 2-3 mg)
was placed in a closed aluminum pan. An empty pan was used
as a reference. Electrochemical measurements were performed
with an Autolab M101 potentiostat. Standard, three electrode
setup consisting of platinum wire working electrode, platinum wire
counter electrode and silver wire quasi-reference electrode
calibrated vs. ferrocene/ferrocenium redox couple prior to each
experiment was used. All electrochemical experiments were
Experimental section
General information: All organic chemicals and solvents were
purchased from Sigma-Aldrich, TCI, SD Fine, and AVRA and
were used without further purification. NMR spectra were taken
on Bruker 400 MHz using CDCl3 as the solvent with
tetramethylsilane as an internal standard. Melting points were
measured on a microprocessor- based melting point apparatus
and were not corrected. HRMS values were obtained on a Jeol
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10.1002/ejoc.201901711
European Journal of Organic Chemistry
FULL PAPER
conducted
in
electrolyte:
0.1
M
solution
of
refluxed for 24 hrs. After that, the mixture was cooled to room
temperature, and then the crude product was extract with ethyl
acetate (3X30 mL) and finally dried with sodium sulfate. It was
then purified by chromatography using Hexane/Ethyl acetate (9:1)
as an eluent to obtain the product as white powder (2a-j). The
characterization of compounds 2a-j were matched with previous
reported work.43 Quantitative yield: 75-90%.
Tetrabutylammoniumhexafluorophosphate (Bu4NPF6) (TCI) in
dichloromethane (Chromasolv, HPLC grade). Solutions were
degassed with argon prior to experiments and kept in an inert
atmosphere during measurements. Onset of oxidation was used
for calculation of ionization potential (IPCV) of compounds. While,
onset of reduction was used for calculation of electron affinity
(EACV) of compounds. The ionization potential (Ip(PE)) of the solid
state sample was measured by photoelectron emission
spectrometry in air as described before in Ref [2]. Indium tin oxide
(ITO)/thick layer of compounds/Al were fabricated by depositing
organic layers under vacuum of 2 X10−6 mBar. The charge carrier
mobility (µ) measurements of vacuum deposited layer were
carried out by the time of flight method (TOF). The TOF
experimental setup consisted of a pulsed Nd:YAG laser (EKSPLA
NL300, a wavelength of 355 nm, pulse duration 3–6 ns), a
Synthesis of 5-(4'-(1-phenyl-1H-
phenanthro[9,10-d]imidazol-2-yl)-[1,1'-
biphenyl ]-4-yl)-
7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine and
their derivatives (3a-j)
A mixture of compound 1 (0.250 g, 6.2 mmol), compound 2a-j
(6.82 mmol), Pd(PPh3)4 (72 mg, 0.062 mmol) and Cs2CO3 (0.404
g, 12.4 mmol) in dioxane/H2O (4:1) 5 mL was stirred under
nitrogen at 80 °C for 24 h. After cooling to room temperature, the
reaction mixture was extracted with dichloromethane, and the
mixture was further purified by column chromatography (8:2) to
obtain a yellow solid 3a-j (Yield: 60-78%).44
Keithley 6517B electrometer,
a
Tektronix TDS 3052C
oscilloscope, and was as described. The transit time (ttr) with the
applied bias (V) indicated the passage of charges through the
entire thickness (d) of the samples. Hole mobility was calculated
as µ=d2/U·tr. OLEDs were prepared by vacuum deposition of
organic and metal layers onto pre-cleaned ITO coated glass
substrate under pressure lower than 2X10−6 mBar. Keithley
6517B electrometer, calibrated photodiode and Keithley 2400C
source meter were used for recording current density via voltage
and luminance via voltage characteristics.
Synthesis of 5-(4-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)phenyl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine (1)
Synthesis of 5-(4-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)phenyl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine (1)
Yellow solid; (Yield 62%); Melting point: 302-304 ºC; FTIR (KBr
cm-1): 3323, 3070, 2966, 2839, 1606, 1548, 1483, 1425, 1402,
1342, 1259, 1165, 1103, 1043, 1016, 945, 891, 840, 804, 740; 1H
NMR (400 MHz, CDCl3) TM ppm: 1.36 (s, 12H, CH2), 2.78 – 2.75
(t, 2H, J=8Hz, CH2) , 2.96 – 2.93 (m, 2H, CH2), 3.15 – 3.06 (m,
4H, CH2), 6.88 – 6.87 (d, 2H, J=4Hz, ArCH), 7.12 – 7.08 (m, 1H,
ArCH), 7.35 – 7.22 (m, 4H, ArCH), 7.46 – 7.44 (d, 2H, J=8Hz,
ArCH), 7.51 – 7.49 (d, 1H, J=8Hz, ArCH), 7.78 – 7.76 (d, 2H,
J=8Hz, ArCH), 13C NMR {1H} (100 MHz, CDCl3)TM ppm: 24.9
(6XCH), 29.2 (CH), 29.4 (CH), 29.5 (CH), 30.9 (CH), 33.1 (CH),
83.8 (C), 125.8 (C), 126.0 (C), 126.8 (C), 127.0 (C), 127.5 (C),
127.6 (C), 127.8 (C), 128.7 (C), 128.9 (C), 129.2 (C), 129.4 (C),
129.7 (C), 132.8 (C), 133.0 (C), 134.7 (C), 138.6 (C), 139.7 (C),
144.8 (C), 145.6 (C), 153.7 (C), 158.1 (C); HRMS (EI-ion trap) for
C33H32BNO2 Calculated [M+] m/z 485.2526, Observed Mass:
485.2523.
A
mixture
of
4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)benzaldehyde (10 mmol) and ammonium acetate (15 mmol)
was taken in a 100 mL conical flask containing 10 mL absolute
ethanol at room temperature, sealed and warmed using water
bath 15 min until the dissolution of the solid contents. After
bringing the reaction mixture to room temperature, 2-teralone (20
mmol) was added, sealed and the mixture was warmed for 5 min
and the reaction mixture was kept aside for 24 h in an open air.
After the completion of the reaction was monitored by TLC. The
resulting product was purified by the column chromatography
over silica gel (60-120 mesh) using n-hexane and ethyl acetate
mixture (9:1) as eluent to give the compound (1). Thus obtained
solid was further purified by recrystallizing in 1:1 ethanol and
tetrahydrofuran mixture to afford compound (1) 65% as a yellow
solid.42
5-(4'-(1-phenyl-1H-phenanthro[9,10-d]imidazol-
2-yl)-[1,1'-biphenyl]-4-yl)-7,8,13,14-
Synthesis of 2-(4-Bromophenyl)-1-phenyl-1H-
phenanthro- [9,10-d]imidazole (PI) and their
derivatives (2a-j)
tetrahydrodibenzo[a,i]phenanthridine(3a)
Yellow solid; (Yield 78%); Melting point: 336-338 ºC; FTIR (KBr
cm-1): 2935, 2845, 1548, 1452, 1392, 1234, 1145, 1001, 941, 827,
746, 698, 617; 1H NMR (400 MHz, CDCl3) TM ppm: 2.81 – 2.78 (t,
2H, J= 6.8Hz, CH2), 2.98 – 2.95 (t, 2H, J= 8 Hz, CH2), 3.17 – 3.09
(m, 4H, CH2), 6.93 – 6.90 (t, 1H, J= 8 Hz, ArCH), 7.00 – 6.98 (d,
1H, J= 8 Hz, ArCH), 7.16 – 7.12 (t, 1H, J= 8 Hz, ArCH), 7.20 –
A mixture of 9, 10-phenanthrenequinone (10.0 mmol), aniline
derivatives (10.0 mmol), 4-Bromobenzaldehyde (10.0 mmol),
ammonium acetate (15.0 mmol), and acetic acid (15 mL) was
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10.1002/ejoc.201901711
European Journal of Organic Chemistry
FULL PAPER
7.18 (d, 1H, J= 8 Hz, ArCH), 7.37 – 7.25 (m, 7H, ArCH), 7.58 –
7.49 (m, 10H, ArCH), 7.67 – 7.63 (t, 6H, J= 8 Hz, ArCH), 7.77 –
7.73 (t, 1H, J= 8 Hz, ArCH), 8.72 – 8.70 (d, 1H, J= 8 Hz, ArCH),
8.79 – 8.76 (d, 1H, J= 8 Hz, ArCH), 8.91 – 8.89 (d, 1H, J= 8 Hz,
ArCH): 13C NMR {1H} (400 MHz, CDCl3)TM ppm: 29.2 (CH), 29.4
(CH), 29.5 (CH), 33.1 (CH), 120.8 (C), 122.8 (C),123.0 (C), 123.1
(C), 124.1 (C), 124.8 (C), 125.6 (C), 125.7 (C), 126.1 (C), 126.2
(C), 126.7 (4XC), 126.9 (C), 127.1 (C), 127.2 (C), 127.3 (C), 127.5
(4XC), 127.7 (C), 127.8 (C), 128.2 (C), 128.7 (C), 128.9 (4XC),
129.1 (C), 129.3 (C), 129.4 (C), 129.6 (2XC), 129.8 (C), 130.2
(2XC), 130.3 (C), 137.5 (C), 138.7 (C), 138.8 (C), 139.5 (C), 139.6
(C), 141.0 (C), 141.3 (C), 145.8 (C), 150.6 (C), 153.3 (C), 158.2
(C); HRMS (EI-ion trap) for C54H37N3 Calculated [M+] m/z:
727.2987, Observed Mass: 727.2985.
ArCH), 8.89 – 8.87 (d, 1H, J= 8 Hz, ArCH);13C NMR {1H} (400
MHz, CDCl3)TM ppm: 29.2 (CH), 29.4 (CH), 29.5 (CH), 33.1 (CH),
117.2 (C), 117.4 (C), 120.6 (C), 122.8 (C), 122.9 (C), 123.1 (C),
124.2 (C), 125.0 (C), 125.7 (C), 126.0 (C), 126.3 (C), 126.8 (C),
126.9 (4xC), 127.1 (C), 127.1 (C), 127.3 (C), 127.6 (C), 127.7
(4XC), 127.9 (C), 128.2 (C), 128.3 (C), 128.7 (C), 128.9 (4XC),
129.1 (C), 129.3 (C), 129.7 (C), 130.4 (C), 130.9 (C), 131.0 (C),
132.9 (C), 133.0 (C), 134.8 (C), 137.5 (C), 138.7 (C), 139.4 (C),
139.7 (C), 141.2 (C), 141.5 (C), 145.8 (C), 150.76 (C), 153.2 (C),
158.2 (C); HRMS (EI-ion trap) for C54H36FN3 Calculated [M+] m/z:
745.2893, Observed Mass: 745.2890.
5-(4'-(1-(4-chlorophenyl)-1H-phenanthro[9,10-
d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine(3d)
5-(4'-(1-(p-tolyl)-1H-phenanthro[9,10-
d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine(3b)
Yellow solid; (Yield 64%); Melting point: 330-332 ºC; FTIR (KBr
cm-1): 3059, 2945, 2845, 1608, 1492, 1396, 1271, 1232, 1166,
1002, 948, 833, 748, 696, 617; 1H NMR (400 MHz, CDCl3) TM ppm:
2.81 – 2.73 (m, 2H, CH2), 2.98 -2.93 (m, 2H, CH2), 3.17 – 3.08 (m,
4H, CH2), 6.70 – 6.68 (d, 1H, J= 8 Hz, ArCH), 7.00 – 6.87 (m, 4H,
ArCH), 7.16 – 7.08 (m, 1H, ArCH), 7.37- 7.21 (m, 2H, ArCH), 7.68
– 7.49 (m, 10H, ArCH), 7.77-7.73 (t, 1H, J= 8 Hz, ArCH), 8.89 –
8.70 (m, 2H, ArCH); 13C NMR {1H} (400 MHz, CDCl3)TM ppm: 29.2
(CH), 29.4 (CH), 29.5 (CH), 30.9 (CH), 33.1 (CH), 115.8 (C),
120.6 (C), 122.8 (C), 123.1 (C), 124.2 (C), 125.0 (C), 125.6 (C),
125.7 (C), 126.0 (C), 126.4 (4XC), 126.8 (C), 126.9 (C), 126.9 (C),
127.1 (C), 127.4 (4XC), 127.6 (C), 127.7 (C), 127.8 (C), 127.9 (C),
128.0 (C), 128.3 (C), 128.7 (4XC), 129.3 (C), 129.5 (C), 129.7 (C),
130.4 (C), 130.4 (C), 130.5 (C), 131.1 (C), 133.0 (C), 135.8 (C),
138.7(C), 139.6 (C), 141.2 (C), 141.4 (C), 145.8 (C), 150.6 (C),
153.2 (C), 157.9 (C), 158.2 (C); HRMS (EI-ion trap) for C23H18ClN2
Calculated [M+] m/z: 761.2598, Observed Mass: 761.2591.
Yellow solid; (Yield 74%); Melting point: 308-310 ºC; FTIR (KBr
cm-1): 3032, 2954, 2926, 2845, 1776, 1608, 1518, 1452, 1390,
1232, 1159, 1033, 950, 825, 748, 721, 619; 1H NMR (400 MHz,
CDCl3) TM ppm: 2.55 (s, 3H, CH3), 2.80 – 2.79 (m, 2H, CH2),
2.98 – 2.94 (m, 2H, CH2), 3.17-3.09 (m, 4H, CH2), 7.05 – 6.89
(m, 2H, ArCH), 7.17 – 7.12 (m, 1H, ArCH), 7.45 – 7.22 (m, 12H,
ArCH), 7.62- 7.49 (m, 9H, ArCH), 7.69 – 7.65 (t, 2H, J= 8 Hz,
ArCH), 7.76 – 7.72 (t, 1H, J=8 Hz, ArCH), 8.71 – 8.69 (d, 1H, J=
8 Hz, ArCH), 8.77 – 8.75 (d, 1H, J= 8 Hz, ArCH), 8.90 – 8.88 (d,
1H, J= 8 Hz, ArCH); 13C NMR {1H} (400 MHz, CDCl3)TM ppm: 21.5
(CH), 29.2 (CH), 29.4 (CH), 29.5 (CH), 33.1 (CH), 119.9 (C),
120.9 (C), 122.7 (C), 123.1 (C), 124.0 (C), 124.8 (C), 125.5 (C),
125.7 (C), 125.8 (C), 126.0 (C), 126.2 (C), 126.7 (2XC), 126.9 (C),
127.0 (C), 127.0 (C), 127.2 (C), 127.6 (2XC), 127.7 (C), 127.8 (C),
128.2 (C), 128.3 (2xC), 128.7 (C), 128.8 (C), 128.9 (C), 129.2
(2XC), 129.5 (C), 129.6 (2XC), 130.2 (C), 130.3 (C), 130.8 (C),
132.9 (C), 133.0 (C), 136.1 (C), 137.4 (C), 138.7 (C), 139.5 (C),
139.6 (C), 139.9 (C), 140.1 (C), 141.9 (C), 141.3 (C), 145.8 (C),
150.6 (C), 153.3 (C), 158.2 (C); HRMS (EI-ion trap) for C55H39N3
Calculated [M+] m/z: 741.3144, Observed Mass: 741.3141.
5-(4'-(1-(3,5-dimethylphenyl)-1H-
phenanthro[9,10-d]imidazol-2-yl)-[1,1'-
biphenyl]-4-yl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine(3e)
Yellow solid; (Yield 67%); Melting point: 318-320 ºC; FTIR (KBr
cm-1): 3018, 2943, 2839, 1608, 1469, 1392, 1145, 1001, 947, 831,
5-(4'-(1-(4-fluorophenyl)-1H-phenanthro[9,10-
d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine(3c)
1
TM
748, 725, 619; H NMR (400 MHz, CDCl3)
ppm: 2.43 (s, 6H,
CH3), 2.82 – 2.79 (t, 2H, J= 8 Hz, CH2), 2.99 – 2.95 (t, 2H, J= 8
Hz, CH2), 3.18 – 3.10 (m, 4H, CH2), 6.94 – 6.90 (t, 1H, J= 8 Hz,
ArCH), 7.01 – 6.99 (d, 1H, J= 8 Hz, ArCH), 7.22 – 7.13 (m, 5H,
ArCH), 7.33 – 7.26 (m, 11H, ArCH), 7.38 – 7.34 (t, 1H, J= 8 Hz,
ArCH), 7.54 – 7.50 (m, 5H, ArCH), 7.60 - 7.58 (d, 4H, J= 8 Hz,
ArCH), 7.67 – 7.63 (t, 1H, J= 8 Hz, ArCH), 7.75 – 7.73 (d, 3H, J=
8 Hz, ArCH), 8.72 – 8.70 (d, 1H, J= 8 Hz, ArCH), 8.78 – 7.76 (d,
1H, J= 8 Hz, ArCH), 8.90 – 8.88 (d, 2H, J= 8 Hz, ArCH); 13C NMR
{1H} (400 MHz, CDCl3)TM ppm: 21.1 (CH), 29.2 (CH), 29.5 (CH),
29.6 (CH),33.3 (2XCH), 115.8 (C), 125.8 (C), 126.0 (C), 126.1 (C),
126.5 (4XC), 126.6 (C), 126.9 (C), 126.9 (C), 127.1 (C), 127.4
(4XC), 127.5 (C), 127.7 (C), 127.9 (C), 128.1 (C), 128.2 (4XC),
Yellow solid; (Yield 69%); Melting point: 354-356 ºC; FTIR (KBr
cm-1): 3061, 2954, 2837, 1508, 1450, 1388, 1219, 1149, 1001,
948, 831, 748, 723, 667, 617; 1H NMR (400 MHz, CDCl3) TM ppm:
2.81 – 2.78 (t, 2H, J= 8 Hz, CH2), 2.98 – 2.94 (m, 2H, CH2), 3.17
– 3.09 (m, 4H, CH2), 6.93 – 6.90 (t, 1H, J=8 Hz, ArCH), 7.00 –
6.98 (d, 1H, J= 8 Hz, ArCH), 7.16 – 7.12 (t, 1H, J= 8 Hz, ArCH),
7.21 – 7.19 (d, 1H, J= 8 Hz, ArCH), 7.27 – 7.25 (d, 2H, J= 8 Hz,
ArCH), 7.37 – 7.29 (m, 7H, ArCH), 7.59 – 7.51 (m, 10H, ArCH),
7.68 – 7.63 (m, 3H, ArCH), 7.77 – 7.73 (t, 1H, J= 8 Hz, ArCH),
8.72 – 8.70 (d, 1H, J= 8 Hz, ArCH), 8.79 – 8.77 (d, 1H, J= 8 Hz,
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901711
European Journal of Organic Chemistry
FULL PAPER
128.7 (C), 128.9 (C), 129.0 (C), 129.5 (4XC), 129.6 (C), 129.7 (C),
133.0 (C), 133.1 (2XC), 134.6 (C), 137.0 (C), 138.2 (C), 138.7 (C),
138.8 (2XC), 139.6 (C), 139.7 (C), 140.2 (C), 141.2 (C), 145.8 (C),
146.4 (C), 153.4 (C), 158.2 (C); HRMS (EI-ion trap) for C56H41N3
Calculated [M+] m/z: 755.3300, Observed Mass: 755.3298.
139.6 (C), 141.6 (C), 142.8 (C), 145.8 (C), 150.5 (C), 153.2 (C),
158.2 (C); HRMS (EI-ion trap) for C55H36N4 Calculated [M+] m/z:
752.2940, Observed Mass: 752.2938.
5-(4'-(1-(3,5-dimethoxyphenyl)-1H-
phenanthro[9,10-d]imidazol-2-yl)-[1,1'-
biphenyl]-4-yl)-7,8,13,14-
5-(4'-(1-(4-methoxyphenyl)-1H-
phenanthro[9,10-d]imidazol-2-yl)-[1,1'-
biphenyl]-4-yl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine(3h)
tetrahydrodibenzo[a,i]phenanthridine(3f)
Yellow solid; (Yield 60%); Melting point: 278-280 ºC; FTIR (KBr
cm-1): 2949, 1724, 1593, 1452, 1330, 1236, 1203, 1155, 1041,
999, 945, 831, 746, 725, 617; 1H NMR (400 MHz, CDCl3) TM ppm:
2.81 – 2.78 (t, 2H, J= 6 Hz, CH2), 2.98 – 2.95 (t, 2H, J= 6 Hz, CH2),
3.17 – 3.09 (m, 4H, CH2), 3.80 (s, 6H, OCH3), 6.72 – 6.71 (d, 3H,
J= 4 Hz, ArCH), 6.94 – 6.90 (t, 1H, J= 8 Hz, ArCH), 7.01 – 6.99
(d, 1H, J= 8 Hz, ArCH), 7.16 – 7.13 (t, 1H, J= 8 Hz, ArCH), 7.37 –
7.25 (m, 9H, ArCH), 7.60 – 7.52 (m, 9H, ArCH), 7.67 – 7.63 (t, 1H,
J= 8 Hz, ArCH), 7.78 – 7.72 (m, 3H, ArCH), 8.72 – 8.70 (d, 1H, J=
8 Hz, ArCH), 8.78 – 8.76 (d, 1H, J= 8 Hz, ArCH), 8.89 – 8.87 (d,
1H, J= 8 Hz, ArCH); 13C NMR {1H} (400 MHz, CDCl3)TM ppm: 29.2
(CH), 29.5 (CH), 29.6 (CH), 33.1 (CH), 55.8 (2XCH), 102.0 (C),
102.3 (C), 107.3 (C), 121.1 (C), 122.8 (C), 122.9 (C), 123.1 (C),
124.9 (C), 125.6 (C), 125.8 (C), 126.1 (4XC), 126.4 (C), 126.8 (C),
126.9 (C), 127.1 (C), 127.3 (C), 127.6 (2XC), 127.7 (C), 127.9 (C),
128.1 (C), 128.3 (4XC), 128.9 (C), 129.2 (C), 129.3 (2XC), 129.4
(C), 129.7 (C), 130.3 (2XC), 132.9 (C), 133.0 (C), 138.7 (C), 139.6
(C), 139.7 (C), 140.3 (2XC), 141.0 (C), 141.3 (C), 145.8 (C), 150.3
(C), 153.3 (C), 158.2 (C), 161.8 (C); HRMS (EI-ion trap) for
C56H41N3O2 Calculated [M+] m/z: 787.3199, Observed Mass:
787.3196.
Yellow solid; (Yield 66%); Melting point: 358-360 ºC; FTIR (KBr
cm-1): 2960, 2829, 1608, 1508, 1450, 1394, 1290, 1244, 1166,
1107, 1024, 948, 831, 746, 725, 617; 1H NMR (400 MHz, CDCl3)
TM ppm: 2.82 – 2.78 (t, 2H, J= 8 Hz, CH2), 2.98 – 2.95 (t, 2H, J= 8
Hz, CH2), 3.18 – 3.09 (m, 4H, CH2), 3.97 (s, 3H, OCH3), 6.94 –
6.90 (t, 1H, J= 8 Hz, ArCH), 7.00 – 6.99 (d, 1H, J= 4 Hz, ArCH),
7.16 – 7.10 (m, 3H, ArCH), 7.38 – 7.26 (m, 14H, ArCH), 7.60 –
7.45 (m, 10H, ArCH), 7.77 – 7.64 (m, 4H, ArCH), 8.72 – 8.70 (d,
1H, J= 8 Hz, ArCH), 8.79 – 8.77 (d, 1H, J= 8 Hz, ArCH), 8.90 –
8.88 (d, 1H, J= 8 Hz, ArCH); 13C NMR {1H} (400 MHz, CDCl3)TM
ppm: 29.2 (CH), 29.5 (CH), 29.6 (CH), 33.1 (CH), 55.4 (2XCH),
114.3 (C), 115.6 (C), 125.7 (C), 125.7 (C), 126.0 (C), 126.6 (C),
126.6 (C), 126.9 (4XC), 127.0 (C), 127.4 (C), 127.6 (4XC), 127.7
(C), 127.8 (C), 128.2 (C), 128.4 (4xC), 128.7 (C), 128.9 (C), 129.6
(C), 129.6 (2XC), 129.7 (C), 129.9 (C), 130.3 (C), 130.7 (2XC),
131.2 (C), 131.3 (C), 132.9 (C), 133.5 (C), 134.5 (C), 138.3 (C),
138.7 (C), 138.7 (C), 139.7 (C), 140.3 (C), 141.2 (C), 145.8 (C),
146.8 (C), 153.4 (C), 158.2 (C), 159.2 (C); HRMS (EI-ion trap) for
C55H39N3O Calculated [M+] m/z: 757.3093, Observed Mass:
757.3090.
5-(4'-(1-(4-nitrophenyl)-1H-phenanthro[9,10-
d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine (3i)
4-(2-(4'-(7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridin-5-yl)-
[1,1'-biphenyl]-4-yl)-1H-phenanthro[9,10-
d]imidazol-1-yl)benzonitrile(3g)
Yellow solid; (Yield 68%); Melting point: 268-270 ºC; FTIR (KBr
cm-1): 2954, 1612, 1479, 1394, 1232, 1118, 1001, 948, 831, 750,
725, 617; 1H NMR (400 MHz, CDCl3) TM ppm: 2.82 - 2.79 (t, 2H,
J= 8 Hz, CH2), 2.99 – 2.96 (m, 2H, CH2), 3.19 – 3.10 (m, 4H, CH2),
6.95 – 6.91 (t, 1H, J= 8 Hz, ArCH), 7.01 – 7.00 (d, 1H, J= 8 Hz,
ArCH), 7.18 - 7.11 (m, 2H, ArCH), 7.38 – 7.28 (m, 5H, ArCH), 7.61
– 7.52 (m, 10H, ArCH), 7.71 – 7.68 (m, 3H, ArCH), 7.79 – 7.75
(m, 10H, ArCH), 7.94 – 7.93 (d, 2H, J= 4 Hz, ArCH), 8.73 – 8.71
(d, 1H, J= 8 Hz, ArCH), 8.81 – 8.79 (d, 1H, J= 8 Hz, ArCH), 8.89
– 8.87 (d, 1H, J= 8 Hz, ArCH); 13C NMR {1H} (400 MHz, CDCl3)TM
ppm: 29.2 (CH), 29.5 (CH), 29.6 (CH), 33.2 (CH), 113.9 (C), 117.7
(C), 120.4 (C), 122.4 (C), 122.8 (C), 123.2 (C), 124.4 (C), 125.3
(C), 125.7 (C), 126.0 (C), 126.1 (2xC), 126.5 (C), 126.9 (2xC),
127.0 (2xC), 127.1 (C), 127.5 (C), 127.6 (2xC), 127.7 (C), 127.8
(C), 127.9 (C), 128.4 (2xC), 128.6 (C), 128.7 (2xC), 128.9 (2xC),
129.5 (C), 129.7 (C), 129.8 (2xC), 130.3 (C), 130.4 (C), 132.9 (C),
133.0 (C), 134.0 (C), 138.0 (C), 138.7 (C), 139.2 (C), 139.7 (C),
141.6 (C), 142.8 (C), 145.8 (C), 150.5 (C), 153.2 (C), 158.2 (C);
Yellow solid; (Yield 72%); Melting point: 328-330 ºC; FTIR (KBr
cm-1): 2978, 1604, 1508, 1452, 1396, 1253, 1166, 1118, 1004,
950, 831, 748, 725, 617; 1H NMR (400 MHz, CDCl3) TM ppm: 2.81
– 2.78 (t, 2H, J= 8 Hz, CH2), 2.98 – 2.95 (t, 2H, J= 8 Hz, CH2),
3.17 – 3.09 (m, 4H, CH2), 6.94 – 6.90 (t, 1H, J= 8 Hz, ArCH), 7.00
– 6.98 (d, 1H, J= 8 Hz, ArCH), 7.26 – 7.10 (m, 2H, ArCH), 7.37 –
7.25 (m, 7H, ArCH), 7.60 – 7.51 (m, 10H, ArCH), 7.70 – 7.66 (m,
3H, ArCH), 7.78 – 7.74 (t, 1H, J= 8 Hz, ArCH), 7.93 – 7.92 (d, 2H,
J= 4 Hz, ArCH), 8.72 – 8.70 (d, 1H, J= 8 Hz, ArCH), 8.80 – 8.78
(d, 1H, J= 8 Hz, ArCH), 8.88-8.86 (d, 1H, J= 8 Hz, ArCH); 13C
NMR {1H} (400 MHz, CDCl3)TM ppm: 29.2 (CH), 29.4 (CH), 29.5
(CH), 33.1 (CH), 113.9 (C), 117.7 (C), 120.4 (C), 122.4 (C), 122.8
(C), 123.1 (C), 124.4 (C), 125.2 (C), 125.7 (C), 126.0 (C), 126.0
(4XC), 126.5 (C), 126.9 (C), 127.0 (C), 127.1 (C), 127.5 (4XC),
127.6 (C), 127.7 (C), 127.9 (C), 128.4 (C), 128.6 (C), 128.7 (4XC),
128.9 (C), 129.4 (C), 129.6 (C), 129.8 (C), 130.2 (C), 130.4 (C),
132.9 (C), 133.0 (C), 134.0 (C), 138.0 (C), 138.7 (C), 139.1 (C),
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901711
European Journal of Organic Chemistry
FULL PAPER
HRMS (EI-ion trap) for C54H36N4O2 Calculated [M+] m/z: 772.2838, 130.1 (C), 130.1 (C), 130.4 (C), 130.6 (C), 120.6 (C), 130.7 (C),
Observed Mass: 772.2838.
130.9 (C), 131.3 (C), 131.8 (C), 131.8 (C), 132.7 (C), 133.5 (C),
137.5 (C), 138.2 (C), 138.6 (C), 141.9 (C), 143.7 (C), 143.3 (C),
144.3 (C), 144.9 (C), 153.2 (C), 156.7 (C), 160.3 (C), 160.7 (C),
161.2 (C), 161.6 (C); HRMS (EI-ion trap) for C53H36N4 Calculated
[M+] m/z: 728.2940, Observed Mass: 728.2938.
5-(4'-(1-(pyridin-2-yl)-1H-phenanthro[9,10-
d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)-7,8,13,14-
tetrahydrodibenzo[a,i]phenanthridine (3j)
ACKNOWLEDGMENTS
Yellow solid; (Yield 65%); Melting point: 280-282 ºC; FTIR (KBr
cm-1): 3039, 2949, 2835, 1707, 1610, 1550, 1481, 1396, 1232,
1116, 1001, 945, 831, 748, 721, 694, 617; H NMR (400 MHz,
1
The authors thanks to VIT for giving Research associate
fellowship (Ref: VIT/HR/2017/5069). The authors thank to Dr. R.
Srinivasan, SSL-VIT for language editing. This work was
supported by the project of scientific co-operation program
between Latvia, Lithuania and Taiwan “Polymeric Emitters with
Controllable Thermally Activated Delayed Fluorescence for
Solution-processable OLEDs” (grant No. P-LLT-19-14).
CDCl3) TM ppm: 2.92 – 2.89 (t, 2H, J= 8 Hz), 3.08 – 3.05 (t, 2H, J=
6 Hz), 3.27 – 3.25 (t, 2H, J= 8 Hz), 3.42 – 3.39 (t, 2H, J= 8 Hz),
7.02 – 6.87 (m, 2H, ArCH), 7.17 – 7.14 (t, 3H, J= 6 Hz, ArCH),
7.51 – 7.29 (m, 19H, ArCH), 7.60 – 7.58 (d, 1H, J= 8 Hz, ArCH);
13C NMR {1H} (400 MHz, CDCl3)TM ppm: 27.1 (CH), 27.8 (CH),
27.9 (CH), 30.6 (CH), 110.3 (C), 113.1 (C), 117.9 (C), 118.7 (C),
120.9 (C), 124.8 (C), 126.2 (C), 126.8 (C), 127.4 (2XC), 127.6 (C),
127.8 (C), 128.1 (C), 128.1 (C), 128.2 (C), 128.6 (C), 128.8 (C),
128.9 (C), 129.1 (C), 129.3 (C), 129.4 (C), 129.8 (C), 130.0 (C),
Key words: Phenananthridine. Electroluminescence. Blue
luminophore. Electrochemical. Solvatochromism.
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