Phenothiazine-oxadiazole push-pull fluorophores: Combining high quantum efficiency, excellent electrochemical stability and facile functionalization

Article abstract of DOI:10.1016/j.dyepig.2017.06.054

A series of five novel sky-blue to green emitting push-pull fluorophores based on phenothiazine donor and 1,3,4-oxadiazole acceptor were synthesized and characterized. Their doped thin films (5 wt% in PMMA) showed high quantum efficiencies (Ф_PL) from 0.63 to 0.77. These fluorophores also underwent remarkably reversible oxidations and reductions suggesting their excellent electrochemical stability. Facile tuning of photophysical, thermal and electrochemical properties of the fluorophores could be achieved by optimizing the functional group attached to the 1,3,4-oxadiazole moiety. Finally, we propose that further functionalization of these fluorophores can be easily achieved and as a proof of concept the synthesis of a vinyl polymer derivative Poly(PO-Tol) was demonstrated.

Full text of DOI:10.1016/j.dyepig.2017.06.054

Accepted Manuscript
Phenothiazine-oxadiazole push-pull fluorophores: Combining high quantum
efficiency, excellent electrochemical stability and facile functionalization
Michael Y. Wong, Louis M. Leung
PII:
S0143-7208(17)30818-5
10.1016/j.dyepig.2017.06.054
DYPI 6075
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 12 April 2017
Revised Date: 15 June 2017
Accepted Date: 21 June 2017
Please cite this article as: Wong MY, Leung LM, Phenothiazine-oxadiazole push-pull fluorophores:
Combining high quantum efficiency, excellent electrochemical stability and facile functionalization, Dyes
and Pigments (2017), doi: 10.1016/j.dyepig.2017.06.054.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Phenothiazine-Oxadiazole Push-Pull Fluorophores:
Combining High Quantum Efficiency, Excellent
Electrochemical Stability and Facile Functionalization
Michael Y. Wong*a and Louis M. Leunga
aDepartment of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong
SAR, China. E-mail: myw1011@gmail.com
Abstract
A series of five novel sky-blue to green emitting push-pull fluorophores based on
phenothiazine donor and 1,3,4-oxadiazole acceptor were synthesized and
characterized. Their doped thin films (5 wt% in PMMA) showed high quantum
efficiencies (ФPL) from 0.63 to 0.77. These fluorophores also underwent remarkably
reversible oxidations and reductions suggesting their excellent electrochemical
stability. Facile tuning of photophysical, thermal and electrochemical properties of the
fluorophores could be achieved by optimizing the functional group attached to the
1,3,4-oxadiazole moiety. Finally, we propose that further functionalization of these
fluorophores can be easily achieved and as a proof of concept the synthesis of a vinyl
polymer derivative Poly(PO-Tol) was demonstrated.
(Keywords: push-pull; donor-acceptor; structure-property relationship; intramolecular
charge-transfer)
Introduction
Push-pull donor-acceptor (D-A) architecture has been extensively employed in
optoelectronic materials [1-13]. For example, thermally activated delayed
1

ACCEPTED MANUSCRIPT
fluorescence (TADF) is a recent important advance in organic light-emitting diode
(OLED) technology for singlet harvesting without the use of organometallic
complexes based on rare metals, the gist of which requires a D-A architecture to
separate the highest occupied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO) so that a vanishing splitting energy (∆EST) is realized [1-
6]. In addition, D-A architecture is essential in many organic photovoltaics (OPV)
materials to facilitate charge dissociation and to extend their absorption into the
visible region [7-11].
Phenothiazine is a favorable constituent in many optoelectronic materials due to its
numerous attractive intrinsic properties. Firstly, termed elegantly as “butterfly
conformation”, the two phenyl rings of phenothiazine are twisted, so that undesirable
intermolecular interactions such as excimer formation can be suppressed [7-8,14-15].
This structural feature is essential for dye-sensitized solar cells (DSSCs) because
aggregation of phenothiazine-based dyes is suppressed so that higher power
conversion efficiencies can be achieved [7-8]. Secondly, phenothiazine also forms
highly stable radical cation with outstanding electrochemical stability [16-17]. Finally,
facile transformation of phenothiazine to S,S-dioxide analogues enables convenient
photophysical, thermal and electrochemical properties engineering which can bring
improved performances in electroluminescence efficiency [18-21]. On the other hand,
1,3,4-oxadiazole is a very popular n-type material due to its excellent electron-
injection and electron-transporting capabilities and has been utilized in chemosensors
[22-23], organic semiconductors [24-26] and electroluminescence devices [5,27-28].
Nevertheless, phenothiazine-oxadiazole D-A small molecules with intramolecular
charge-transfer (ICT) character have been underexplored. The work contributed by
Park and co-workers contained a small molecule where phenothiazine was linked to
2

ACCEPTED MANUSCRIPT
1,3,4-oxadiazole via a phenyl bridge but it was a synthetic intermediate whose
physical properties were not studied [29]. Pan et al. reported 10-ethyl-3-(5-methyl-
1,3,4-oxa-diazol-2-yl)-10H-phenothiazine which was structurally very similar to
compound 5 in this study (vide infra), but only the crystal structure was studied [30].
In a patent filed by Ahn et al., two phenothiazine-oxadiazole push-pull fluorophores
were applied as emitters in OLED devices [31]. In addition, Qiu et al. very recently
employed two phenothiazine-oxadiazole fluorophores in the emitting layer of OLED
devices and achieved a maximum external quantum efficiency (EQE) of 5.4% which
is close to the theoretical EQE cap for fluorescent OLEDs, clearly demonstrating the
potency of this class of emitters [5]. However, the phenothiazine-oxadiazole push-pull
fluorophores reported by Ahn and Qiu were structurally very similar and therefore it
leaves room for further investigation of this emitter system. In this contribution, we
synthesized and characterized a series of five novel phenothiazine-oxadiazole D-A
fluorophores (Figures 1, 5-9) where the substituents attached to the oxadiazole moiety
were responsible for tuning the photophysical, electrochemical and thermal properties
of the fluorophores. A S,S-dioxide analogue PO-Tol-SO2 (10) (Figure 1, inset) was
also synthesized where the oxidized phenothiazine resulted in tremendous impact on
the photophysical and electrochemical profiles of these fluorophores due to the loss of
their push-pull character [18]. We shall demonstrate that the phenothiazine-oxadiazole
D-A fluorophores are not only highly emissive but also electrochemically very stable.
Finally, facile functionalization of these D-A fluorophores for tailored purposes is
another attractive merit of this emitter system and we shall demonstrate this by
preparing a vinyl polymer derivative Poly(PO-Tol).
3

ACCEPTED MANUSCRIPT
Figure 1. Chemical structures of the novel phenothiazine-oxadiazole D-A
fluorophores (5-9). Also shown in the inset is PO-Tol-SO2 (10) which is the S,S-
dioxide analogue of PO-Tol (6).
Results and Discussions
Synthesis
Scheme 1. Synthesis of phenothiazine-oxadiazole D-A fluorophores. i) K+t-BuO-,
o
MeI, THF, rt, 30 min ii) POCl3, DMF, chlorobenzene, 70 C, 5 h iii) NH2OH·HCl,
o
o
NMP, 120 C, overnight iv) NaN3, NH4Cl, DMF, 115 C, 2 d v) RCOCl, pyridine,
reflux, overnight.
The synthetic route of the phenothiazine-oxadiazole D-A fluorophores 5-9 is shown in
Scheme 1. The key intermediate tetrazole 4 was generated by Vilsmeier formylation,
cyanation and subsequent cyclization by azide anion. The target 1,3,4-oxadiazole was
formed by reacting 4 with corresponding acid chlorides in refluxing pyridine. The S,S-
4

ACCEPTED MANUSCRIPT
dioxide analogue PO-Tol-SO2 (10) was derived from PO-Tol (6) in an excellent yield
of 99.3% using m-chloroperoxybenzoic acid (mCBPA) as the oxidant. All the
syntheses employed conventional chemistry and can be easily scaled up.
Photophysical Properties
Table 1. Summary of absorption and emission profiles of the phenothiazine-
oxadiazole D-A fluorophores in different matrices.
Absorption
Emissiona
λ
abs (nm) [ε]
λem (nm) [FWHMb] (nm)
(103 M-1 cm-1)
d
DCM
PhMe
464 [67]
477 [68.5]
482 [68]
488 [94]
DCM
ACN
Filmc
Фsol/Фfilm
269 [34.1], 277 [32.2], 348 [6.9]
290 [32.3], 364 [11.5]
298 [27.8], 368 [13.8]
280 [27.0], 364 (sh) [12.7], 387
[13.8]
482 [72]
493 [77]
465 [72.5]
484 [70]
484 [68]
498 [104]
0.51/0.72
0.65/0.77
0.64/0.73
0.51/0.69
5
6
7
8
494 [72.5]
499 [75.5]
529 [106]
502 [80.5]
510 [88.5]
627 [144.5]
d
275 [35.0], 302 (sh) [26.4], 387
[18.6]
530 [94.5] 664 [138.5]
−
529 [110.5] 0.51/0.63
9
261 [16.8], 273 [18.2], 291 [23.8],
332 [43.2]
375 [44]
375 [45]
380 [51.5]
378 [42]
0.50/0.55
10
d
a λex = 360 nm. bFull width at half-maximum. cSpun-coated thin film with 5 wt% sample in PMMA. Solution
PLQY (Фsol) was measured in toluene with quinine sulfate as the reference (PLQY = 0.55 in 1N H2SO4 at 298
K). dEmission too weak to be detectable.
5

ACCEPTED MANUSCRIPT
Figure 2. Absorption spectra of the phenothiazine-oxadiazole D-A fluorophores (5, 8
and 9) and the S,S-dioxide analogue (10) in DCM.
Table 2 summarizes the photophysical properties of the phenothiazine-oxadiazole D-
A fluorophores and Figure 2 shows the absorption spectra of some phenothiazine-
oxadiazole D-A fluorophores under optically dilute solutions in DCM. All the D-A
fluorophores (5-9) exhibited both π-π* transitions from ~280 nm to ~300 nm and
intramolecular charge transfer (ICT) bands from ~350 nm to ~390 nm [32-34].
However, the ICT band was absent in 10 due to the loss of electron-donating ability of
the phenothiazine moiety after the introduction of S,S-dioxide functional group [18].
In general, the ICT absorption maxima depended on the conjugation lengths and the
electronic effects of the functional group attached to the oxadiazole moiety. For
example, 5 showed the highest-energy ICT absorption maximum at 348 nm due to
shortest conjugation length of the methyl group. Replacements of methyl group with
6

ACCEPTED MANUSCRIPT
toluyl and thiophene functionalities increased conjugation lengths and resulted in red-
shifts in ICT band by 16 nm and 20 nm as observed in 6 and 7 respectively. On the
other hand, 9 showed the lowest-energy ICT absorption maximum at 387 nm due to
the electron-withdrawing 2,3-diphenylquinoxaline group. The absorption maxima of
the D-A fluorophores were nearly identical irrespective of the solvents (Supporting
Information Table S1), suggesting the absence of positive solvatochromism due to
their relatively low polarity in the ground state [35-39].
Figure 3. Normalized emission spectra of 6 in toluene, DCM and acetonitrile (solvent
dielectric constants ε listed in bracket) [40] showing positive solvatochromism.
The phenothiazine-oxadiazole D-A fluorophores thin films (5 wt% in PMMA)
exhibited high quantum efficiencies (0.63-0.77) and in particular 5-7 emitted sky-blue
light (λPL: 465-484 nm), suggesting their high potential as emitters for OLED
applications. In general, the quantum efficiencies in toluene (0.51-0.64) were lower
than those of thin films which can be explained by the more rigid matrix in the latter
to suppress non-radiative quenching pathways [4]. The emission energies of the
7

ACCEPTED MANUSCRIPT
phenothiazine-oxadiazole D-A fluorophores demonstrated a similar trend as the
absorption profile and could be easily tuned by the functional group attached to the
oxadiazole moiety. For example, while 5 showed the bluest emission (film λPL: 465
nm), 9 gave the lowest emission energy (film λPL: 529 nm) among the series with the
help of strongly electron-withdrawing 2,3-diphenylquinoxaline group. However,
unlike the absorption study which showed little dependence on the choice of solvents,
positive solvatochromism was evident in the emission spectra. For example, the
emission maxima of 6 red-shifted when the polarity of the solvents increased (Figure
3) which was due to the dipolar stabilization of the highly polar excited state [35-39].
When the phenothiazine was oxidized to S,S-dioxide, the D-A architecture was lost
and hence no positive solvatochromism was observed in 10 [18].
Electrochemical Properties
Table 2. Summary of electrochemical profiles of the phenothiazine-oxadiazole D-A
fluorophores by cyclic voltammetry.a
Oxidations
Reductions
ox
oxb
red
redd
E1/2
∆Ep
HOMOc
(eV)
E1/2
∆Ep
LUMOe
(eV)
Band gap
(eV)
3.01
(V vs Fc/Fc+)
0.44
(mV)
73
(V vs Fc/Fc+)
-2.57
(mV)
71
-5.24
-5.24
-5.24
-5.26
-5.26
-6.19
-2.23
-2.29
-2.31
-2.42
-2.52
-2.75
5
6
0.44
79
-2.51
64
2.95
0.44
68
-2.49
76
2.93
7
0.46
75
-2.38
74
2.84
8
0.46
76
-2.28
73
2.74
9
f
1.39
−
-2.05
74
3.44
10
aMeasured in degassed THF under argon with 0.1 M nBu4NPF6 as the supporting electrolyte.
c
bPeak-to-peak separations for oxidation processes. HOMO energies were calculated using the
8

ACCEPTED MANUSCRIPT
ox
relation EHOMO = − (E1/2ox + 4.8) eV, where E1/2 is the oxidation potential with respect to E1/2 of
d
e
ferrocene/ferrocenium redox couple. Peak-to-peak separations for reduction processes. LUMO
red
red
energies were calculated using the relation ELUMO = − (E1/2 + 4.8) eV, where E1/2 is the
f
reduction potential with respect to E1/2 of ferrocene/ferrocenium redox couple. Irreversible
oxidation.
The electrochemical properties of the phenothiazine-oxadiazole D-A fluorophores
were studied by cyclic voltammetry in degassed THF under argon with 0.1 M
nBu4NPF6 as the supporting electrolyte and the data are summarized in Table 2.
Fluorophores 5-9 possessed similar HOMO energy levels (from -5.24 eV to -5.26 eV)
which suggested that the HOMO was mainly located on the phenothiazine moiety and
the functional groups attached on the oxadiazole moiety were too remote to have
observable effect on the HOMO. On the contrary, the LUMO energy levels were
strongly affected by the substituents attached on the oxadiazole. For example, 9-
anthracenyl and 6-(2,3-diphenylquinoxalinyl) groups resulted in much deeper LUMO
energy levels of -2.42 eV and -2.52 eV respectively in 8 and 9, suggesting the
LUMOs were subjected to conjugation length and electron-withdrawing effects of the
substituents. These fluorophores also showed highly reversible oxidations and
reductions due to remarkably stable phenothiazine radical cation and oxadiazole
radical anion, as demonstrated in Figure 4 that the cyclic voltammogram profile of 6
did not change at all after 10 repeated cycles. Hence, the fluorophores have excellent
redox reversibility which is crucial to the stability of optoelectronic devices. In
ox
addition, the peak-to-peak separations for both oxidations (∆Ep ) and reductions
(∆Epred) of fluorophores 5-9 ranged from 68 to 79 mV and from 64 to 79 mV
respectively, which are close to the theoretical 59 mV for an one-electron process.
Oxidation of the phenothiazine strongly suppressed the donor ability of the
9

ACCEPTED MANUSCRIPT
phenothiazine moiety and the HOMO was sharply lowered by as large as ~1 eV
(compare 6 and 10). The oxidation of 10 also became irreversible.
Figure 4. Cyclic voltammogram of 6 in degassed THF with 0.1 M nBu4NPF6 as the
supporting electrolyte for 10 cycles. Both the oxidation and reduction were highly
reversible and did not change at all after 10 repeated scans, suggesting desirable
electrochemical stability of this class of phenothiazine-oxadiazole D-A fluorophores.
Thermal Properties
Table 3. Summary of thermal properties of the phenothiazine-oxadiazole D-A
fluorophores.
a
Tg (oC)
Tmb (oC)
170
Tonsetc (oC)
365
d
−
5
10

ACCEPTED MANUSCRIPT
d
−
144
408
408
419
446
474
6
7
103
104
125
104
168
235
245
252
8
9
10
b
c
aGlass-transition temperature. Melting point Decomposition onset temperature at 5 wt%
loss. dNot detected.
The glass-transition temperatures (Tg) and the decomposition onset temperatures
(Tonset) of the phenothiazine-oxadiazole D-A fluorophores were probed by differential
scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques
respectively and the results are summarized in Table 3. DSC and TGA thermograms
of some D-A fluorophores are shown in Supporting Information (Figure S17-S19).
High Tg is crucial to the film morphological stability against crystallization due to
joule heat formation during the OLED device operation [41-42]. It is evident that the
choice of functional group attached to the oxadiazole moiety could affect the Tg of the
D-A fluorophores. For example, the incorporation of 2,3-diphenylquinoxaline group
in 9 greatly enhances Tg to 125oC due to its higher molecular weight [43-44] and
polarity [43,45]. In addition, oxidation of the phenothiazine to S,S-dioxide results in
higher thermal stability which can be deduced by comparing the Tg, melting point and
onset decomposition temperature (Tonset) between fluorophores 10 and 6. In general,
the phenothiazine-oxadiazole D-A fluorophores are thermally robust with Tg > 100oC
and Tonset > 400oC which suit optoelectronic applications.
Further functionalization of phenothiazine-oxadiazole D-A fluorophores for
additional property
11

ACCEPTED MANUSCRIPT
Various aryl/alkynyl groups
Br
CH3
N
N
X
S
N
R
O
O
AIE property
H
H
H
Polymer
Scheme 2. A map showing a number of possible further functionalizations of the
phenothiazine-oxadiazole D-A fluorophores for tailored applications. Bromination
followed by Suzuki or Sonogashira coupling gives a variety of aryl and alkynyl
groups respectively (top route). Friedel-Crafts acylation followed by Knoevenagel
condensation offers the tetraphenylethylene group for AIE property (middle route).
Vilsmeier formylation followed by Wittig reaction gives vinyl monomer which can be
readily polymerized, which was actually achieved in this study (bottom route).
Scheme 3. Preparation of vinyl polymer Poly(PO-Tol) (13) derived from PO-Tol (6).
i) POCl3, DMF, chlorobenzene, 100 oC, overnight ii) K+t-BuO-, CH3Ph3P+Br-, THF, rt,
30 min. iii) AIBN, toluene, 80oC, overnight. Shown at the right are the normalized
12

ACCEPTED MANUSCRIPT
emission of the polymer neat film and its photos of being held by a forceps
demonstrating excellent flexibility in ambient condition (left) and under ultra-violet
irradiation (right).
An additional merit of the phenothiazine-oxadiazole D-A fluorophores is facile
functionalization at the other side of the phenothiazine moiety (i.e. 7-position), thanks
to its strong p-type character and highly regioselective electrophilic aromatic
substitution reactions. As shown in Scheme 2, the phenothiazine-oxadiazole D-A
fluorophores can be brominated followed by Suzuki or Sonogashira coupling to
generate desired aryl or alkynyl derivatives. The fluorophores can also carry out
Friedel-Crafts acylation with benzoyl chloride followed by Knoevenagel condensation
with diphenylmethane to yield the tetraphenylethylene functionality which should
bring about the interesting aggregation-induce emission (AIE) property [46]. As a
proof of concept, we synthesized a vinyl polymer Poly(PO-Tol) (13) based on PO-
Tol (6) as shown in Scheme 3. The D-A fluorophore PO-Tol (6) underwent Vilsmeier
formylation at position 6 to give 11 in a 51.2% yield, followed by Wittig reaction with
methyl triphenylphosphonium bromide as the ylide precursor to generate the vinyl
monomer 12 with an excellent yield of 95.2%. Conventional free-radical
polymerization using catalytic AIBN initiator (1 mol%) in toluene at 80oC offered
Poly(PO-Tol) in a 62.4% yield with a high number-average molecular weight (Mn) of
32,000 Da and a polydispersity index (PDI) of 1.7. The neat film of Poly(PO-Tol)
showed a green emission (λPL: 507 nm) with a high quantum efficiency of 67%.
Therefore, the polymer is an ideal candidate as the emitting layer in organic light-
emitting diodes (OLED) or in light-emitting electrochemical cells (LECs) for its
highly reversible oxidation and reduction (vide supra) which is beneficial to LEC
device performance [47].
13

ACCEPTED MANUSCRIPT
Conclusions
In this study, we have synthesized and characterized a series of five novel
phenothiazine-oxadiazole push-pull fluorophores whose photophysical,
electrochemical and thermal properties could be conveniently tuned by the oxadiazole
substituents. These fluorophores were found to be highly emissive and
electrochemically stable. We have also demonstrated their facile functionalization by
preparing a vinyl polymer derivative. Therefore, we believe that this class of
phenothiazine-oxadiazole push-pull fluorophores are very promising materials in
optoelectronic applications.
Experimental Section
Characterization. Analytical thin-layer-chromatography (TLC) was performed with
silica plates with aluminum backings (250 µm with F-254 indicator). TLC
1
13
visualization was accomplished by 254/365 nm UV lamp. H and C NMR spectra
were recorded with a Bruker-AF301 AT 400 MHz spectrometer using CDCl3 as
solvent and tetramethylsilane as the internal standard. High resolution mass
spectrometry (HRMS) was carried out using a Bruker autoflex MALDI-TOF mass
spectrometer. Elemental analyses were performed using a Perkin-Elmer 2400 Series II
Analyzer. Melting points were taken on differential scanning calorimetry (DSC) or on
a MEL-TEMP capillary tube apparatus without correction. UV-vis absorption spectra
were measured in THF at a 100 ppm concentration using a Varian Cary 200
spectrophotometer. Fluorescence spectra were measured in toluene/DCM/MeCN at a
10 ppm concentration using a Perkin Elmer LS55 Luminescence Spectrometer.
Quantum yields were measured in toluene with quinine sulfate in 1N sulfuric acid as
14

ACCEPTED MANUSCRIPT
the standard (Φ=0.55) with reference to the equation Φs = Φr(Ar/As)((Is/Ir)(ns/nr)2,
where A stands for the absorbance at the excitation wavelength (λex: 360 nm), I is the
integrated area under the corrected emission curve and n is the refractive index of the
solvent, with the subscripts “s” and “r” representing sample and reference respectively
[48]. Doped thin film were obtained by spin-coating a DCM solution (1 mL) of a
mixture of the sample (1 mg) and the PMMA (19 mg) matrix onto a quartz glass.
Differential scanning calorimetry (DSC) analyses were performed on a Perkin-Elmer
Pyris Diamond DSC under nitrogen purge at a heat rate of 20 oC/min.
Thermogravimetric analyses (TGA) were achieved with a Perkin-Elmer TGA-6
o
thermal analyzers under nitrogen at a heat rate of 40 C/min. Cyclic voltammetry
measurements were performed on a BAS CV-50W electrochemical analyzer adapted
with a conventional three-electrode configuration consisting platinum working and
auxiliary electrodes and a Ag/AgCl reference electrode. All measurements were
effected in 0.1 M THF solution with tetrabutylammonium hexafluorophosphate as the
supporting electrolyte and ferrocene as the internal standard. Molecular weights were
determined by Gel Permeation Chromatography (GPC) using a HP 1050 series HPLC
with THF as the eluent and a UV absorption detector (at 254 nm) calibrated against
polystyrene MW standards.
Materials. All the commercially available chemicals and reagent grade solvents were
used as received. Anhydrous THF was obtained from distillation over sodium
benzophenone ketyl. Toluene used in polymerization was distilled fresh once from
calcium hydride and AIBN was recrystallized from methanol before use.
Synthesis
15

ACCEPTED MANUSCRIPT
10-Methylphenothiazine (1)
To a solution of phenothiazine (5 g, 25.1 mmol) in dry THF (30 ml) under stirring at
room temperature blanketed with nitrogen, potassium tert-butoxide (4.22 g, 37.7
mmol) was added. The suspension was allowed to stir for 10 minutes, followed by
dropwise addition of methyl iodide (2.35 ml, 37.7 mmol). After stirring for another 30
minutes, excess hexane (50 ml) was added and the whole mixture was filtered through
a short plug of silica. The silica was then washed with DCM several times. The filtrate
was concentrated and dried under vacuum to give the crude 1 as a purple solid (5.24
o
g, 98%) which was used directly for subsequent procedures. Mp 100.8-101.6 C (lit.
101.7 oC -104.1 oC) [49].
3-Formyl-10-methylphenothiazine (2)
A mixture of 1 (6.74 g, 31.6 mmol), phosphorus oxychloride (16.1 ml, 173 mmol),
dimethylformamide (11.5 ml, 149 mmol) in chlorobenzene (20 ml) was heated at 70
oC for 5 hours. After cooling, ice water was added and the mixture was neutralized by
sat. NaHCO3 (aq). The mixture was then allowed to stir for about another half an hour
to ensure complete hydrolysis of the imine immediate which was then extracted by
DCM (20 mL x 3). The combined organic phase was washed with sat. NaHCO3 (aq)
and then brine. The DCM solution was dried with anhydrous Mg2SO4 and
concentrated in vacuo to give the crude which was purified by flash column
chromatography using EA: Hexane: Triethylamine (1:5:2%) as eluent to offer 2 (6.28
16

ACCEPTED MANUSCRIPT
g, 81.5%) as a yellow solid. mp 83.1-83.9 oC; δH (CDCl3) 9.77 (s, 1 H), 7.63 (dd, J =
8.4 and 2.0 Hz, 1 H), 7.57 (d, J = 2.0 Hz, 1 H) , 7.19-7.14 (m, 1 H), 7.10 (dd, J = 7.6
and 1.6 Hz, 1 H), 6.96 (dt, J = 7.6 and 1.6 Hz, 1 H), 6.83 (d, J = 8.4 Hz, 1 H), 6.82
(dd, J = 8.0 and 0.8 Hz, 1 H), 3.39 (s, 3 H); δC (CDCl3) 189.1, 150.0, 143.0, 130.1,
129.5, 126.9, 126.8, 126.3, 122.9, 122.6, 121.5, 113.8, 112.7, 34.8.
3-Cyano-10-methylphenothiazine (3)
A mixture of 2 (2.91 g, 12.1 mmol) and hydroxylamine hydrochloride (2.52 g, 36.3
o
mmol) in NMP (30 ml) was heated to 120 C overnight. After cooling, water was
added and the mixture was extracted by DCM for several times. The combined
organic phase was washed with water for three times and finally with brine. The DCM
solution was dried by anhydrous Mg2SO4 and concentrated in vacuo to give the crude
which was purified by flash column chromatography using EA: Hexane:
Triethylamine (1:6:2%) as eluent to offer 3 (2.40 g, 83.6%) as a white solid. mp
122.0-122.8 oC; δH (CDCl3) 7.40 (dd, J = 8.0 and 2.0 Hz, 1 H), 7.29 (d, J = 2.0 Hz, 1
H), 7.18 (dt, J = 7.4 and 1.2 Hz, 1 H), 7.09 (dd, J = 7.4 and 1.2 Hz, 1 H), 6.97 (dt, J =
7.4 and 1.2 Hz, 1 H), 6.82 (d, J = 8.0 Hz, 1 H), 6.75 (d, J = 8.0 Hz, 1 H), 3.36 (s, 3
H); δC (CDCl3) 149.6, 144.1, 132.0, 130.0, 128.0, 127.4, 124.5, 123.7, 122.0, 118.9,
114.8, 114.0, 105.3, 35.6.
3-(2H-tetrazol-5-yl)-10-methylphenothiazine (4)
A mixture of 3 (760 mg, 3.19 mmol), sodium azide (621 mg, 9.55 mmol) and
17

ACCEPTED MANUSCRIPT
ammonium chloride (511 mg, 9.55 mmol) in DMF (20 ml) was heated at 115 oC for 2
days. After cooling, the reaction mixture was poured into water and acidified to pH 1
by conc. HCl (aq). The solid precipitated was filtered and air-dried overnight to offer
4 (780 mg, 86.9%) as a grey solid which was pure enough to be used directly in the
o
next step. Mp: decomposed at 130 C evidenced by gas formation (powder expanded
from inside out and turned into foam.) δH (DMSO-d6) 7.88 (dd, J = 8.5 and 2.0 Hz, 1
H), 7.78 (d, J = 2.0 Hz, 1 H), 7.27-7.23 (m, 1 H), 7.20 (dd, J = 7.9 and 1.6 Hz, 1 H),
7.14 (d, J = 8.6 Hz, 1 H), 7.03-6.99 (m, 2 H), 3.38 (s, 3 H); δC (DMSO-d6) 148.1,
144.8, 128.6, 127.4, 127.3, 125.4, 123.6, 123.5, 121.6, 118.4, 115.6, 35.9.
General Procedures for the preparation of Phenothiazine-Oxadiazole Push-Pull
Fluorophores (5-9)
3-[5-(4-Toluyl)-1,3,4-oxadiazol-2-yl]-10-methylphenothiazine (PO-Tol, 6)
p-Toluyl chloride (0.18 ml, 1.36 mmol) was added dropwise to a solution of 4 (192
mg, 0.68 mmol) in dry pyridine (2 ml) and refluxed overnight. After cooling, 10%
HCl (aq) (10 ml) was added to the mixture which was then extracted by DCM for
several times. The combined organic was washed with sat. NaHCO3 (aq) and then
brine. The DCM solution was dried by anhydrous Mg2SO4 and concentrated in vacuo
to give the crude which was purified by flash column chromatography using EA:
Hexane: Triethylamine (1:4:2%) as eluent to offer 6 (142 mg, 48.9% from 3) as a
18

ACCEPTED MANUSCRIPT
o
green solid. mp 143.4-144.2 C; δH (CDCl3) 7.98 (d, J = 8.0 Hz, 2 H), 7.91 (dd, J =
8.4 and 2.0 Hz, 1 H), 7.83 (d, J = 1.6 Hz, 1 H), 7.31 (d, J = 8.0 Hz, 2 H), 7.19-7.12
(m, 2 H), 6.96 (t, J = 7.6 Hz, 1 H), 6.86 (d, J = 8.4 Hz, 1 H), 6.83 (d, J = 8.0 Hz, 1
H), 3.40 (s, 3 H), 2.41 (s, 3 H); δC (CDCl3) 164.4, 163.8, 148.6, 144.6, 142.2, 129.8,
127.8, 127.3, 126.8, 126.6, 125.3, 124.2, 123.3, 122.5, 121.2, 118.0, 114.5, 114.1,
35.6, 21.7; Anal. Calcd. for C22H17N3OS: C, 71.14%; H, 4.61%; N, 11.31%. Found:
C, 70.98%; H, 4.56%; N, 11.55%. HRMS (MALDI) calcd for C22H17N3OS: 371.1092;
found: 371.1088.
3-[5-Methyl-1,3,4-oxadiazol-2-yl]-10-methylphenothiazine (PO-Me, 5)
o
Yield: 42.0% from 3. Yellow solid, mp 169.5-170.4 C; δH (CDCl3) 7.79 (d, J = 7.6
Hz, 1 H), 7.73 (s, 1 H), 7.19-7.11 (m, 2 H), 6.95 (t, J = 7.2 Hz, 1 H), 6.83 (d, J = 7.6
Hz, 1 H), 6.82 (d, J = 7.6 Hz, 1 H), 3.39 (s, 3 H), 2.57 (s, 3 H); δC (CDCl3) 164.3,
163.2, 148.5, 146.7, 127.7, 127.3, 126.3, 125.2, 124.2, 123.2, 122.6, 118.0, 114.5,
114.1, 35.6, 11.7; Anal. Calcd. for C16H13N3OS: C, 65.07%; H, 4.44%; N, 14.23%.
Found: C, 64.83%; H, 4.56%; N, 14.30%. HRMS (MALDI) calcd for C16H13N3OS:
295.0779; found: 295.0768.
3-[5-(2-Thiophenyl)-1,3,4-oxadiazol-2-yl]-10-methylphenothiazine (PO-Th, 7)
19

ACCEPTED MANUSCRIPT
o
Yield: 66.7% from 3. Green solid, mp 167.4-168.1 C; δH (CDCl3) 7.88 (dd, J = 8.4
and 2.0 Hz, 1 H), 7.80 (d, J = 2.0 Hz, 1 H), 7.79 (dd, J = 3.6 and 1.2 Hz, 1 H), 7.53
(dd, J = 5.2 and 1.2 Hz, 1 H), 7.20-7.15 (m, 2 H), 7.13 (dd, J = 7.6 and 1.6 Hz, 1 H),
6.96 (dt, J = 7.4 and 0.8 Hz, 1 H), 6.85 (d, J = 8.8 Hz, 1 H), 6.83 (dd, J = 8.0 and 0.8
Hz, 1 H), 3.39 (s, 3 H); δC (CDCl3) 163.5, 160.5, 148.8, 144.6, 130.0, 129.6, 128.2,
127.8, 127.3, 126.6, 125.3, 124.2, 123.3, 122.5, 117.6, 114.6, 114.1, 35.6; Anal.
Calcd. for C19H13N3OS2: C, 62.79%; H, 3.61%; N, 11.56%. Found: C, 62.88%; H,
3.56%; N, 11.31%. HRMS (MALDI) calcd for C16H13N3OS2: 363.0500; found:
363.0516.
3-[5-(9-Anthracenyl)-1,3,4-oxadiazol-2-yl]-10-methylphenothiazine (PO-An, 8)
o
Yield: 46.1% from 3. Yellow solid, mp 234.6-235.6 C; δH (CDCl3) 8.66 (s, 1 H),
8.08-7.94 (m, 5H), 7.87 (d, J = 2.0 Hz, 1 H), 7.54-7.51 (m, 4H), 7.17 (t, J = 8.0 Hz, 1
H), 7.11 (d, J = 7.2 Hz, 1 H), 6.95 (t, J = 7.6 Hz, 1 H), 6.88 (d, J = 8.4 Hz, 1 H), 6.83
(d, J = 8.0 Hz, 1 H), 3.42 (s, 3 H); δC (CDCl3) 165.3, 162.6, 148.9, 144.6, 131.4,
131.0, 128.8, 127.7, 127.1, 126.8, 125.7, 125.5, 125.4, 125.1, 124.4, 123.3, 122.5,
117.9, 117.3, 114.6, 114.2, 35.6; Anal. Calcd. for C29H19N3OS: C, 76.13%; H,
4.19%; N, 9.18%. Found: C, 76.28%; H, 4.11%; N, 9.30%. HRMS (MALDI) calcd
for C29H19N3OS: 457.1249; found: 457.1255.
3-[5-(2,3-Diphenylquinoxalin-6-yl)-1,3,4-oxadiazol-2-yl]-10-methylphenothiazine
(PO-QX, 9)
20

ACCEPTED MANUSCRIPT
o
Yield: 55.9% from 3. Orange solid, mp 244.6-245.4 C; δH (CDCl3) 8.87 (d, J = 1.6
Hz, 1 H), 8.54 (dd, J = 8.8 and 2.0 Hz, 1 H), 8.29 (d, J = 9.2 Hz, 1 H), 7.96 (dd, J =
8.4 and 2.0 Hz, 1 H), 7.90 (d, J = 2.0 Hz, 1 H), 7.54-7.52 (m, 4H), 7.38-7.33 (m, 6H),
7.20-7.14 (m, 2 H), 6.98 (dt, J = 7.4 and 0.8 Hz, 1 H), 6.91 (d, J = 8.8 Hz, 1 H), 6.85
(d, J = 8.0 Hz, 1 H), 3.43 (s, 3 H); δC (CDCl3) 164.7, 163.5, 154.8, 154.7, 149.0,
144.5, 142.5, 140.9, 138.6, 138.5, 130.4, 129.9, 129.3, 128.4, 127.8, 127.6, 127.4,
126.7, 125.4, 125.1, 124.4, 123.4, 122.5, 117.6, 114.6, 114.2, 35.7; Anal. Calcd. for
C35H23N5OS: C, 74.85%; H, 4.13%; N, 12.47%. Found: C, 75.06%; H, 4.11%; N,
12.30%. HRMS (MALDI) calcd for C35H23N5OS: 561.1623; found: 561.1638.
3-[5-(4-Toluyl)-1,3,4-oxadiazol-2-yl]-10-methylphenothiazine-S,S-dioxide
Tol-SO2, 10)
(PO-
To 6 (250 mg, 0.67 mmol) and an excess of wet m-chloroperoxybenzoic acid (<77%,
1 g) was both dissolved in DCM (10 ml) was allowed to stir overnight. The reaction
mixture was then washed with sat. Na2S2O3 (aq) and then brine. The DCM solution
21

ACCEPTED MANUSCRIPT
was dried by anhydrous Mg2SO4 and concentrated in vacuo to give the crude which
was purified by flash column chromatography using EA: Hexane: Triethylamine
o
(1:1:2%) as eluent to offer 10 (267 mg, 99.3%) as a white solid. mp 251.4-252.4 C;
δH (DMSO) 8.58 (d, J = 2.0 Hz, 1 H), 8.42 (dd, J = 8.8 and 2.0 Hz, 1 H), 8.07 (dd, J
= 8.0 and 2.4 Hz, 3 H), 7.85-7.81 (m, 2 H), 7.70 (d, J = 8.4 Hz, 1 H), 7.47-7.43 (m, 3
H), 3.82 (s, 3 H), 2.41 (s, 3 H); δC (DMSO) 164.2, 162.6, 143.4, 142.2, 141.0, 134.0,
131.1, 129.9, 126.7, 123.6, 123.5, 122.9, 122.5, 120.8, 120.5, 118.1, 117.4, 116.7,
36.2, 21.1; Anal. Calcd. for C22H17N3O3S: C, 65.49%; H, 4.25%; N, 10.42%. Found:
C, 65.59%; H, 4.14%; N, 10.36%. HRMS (MALDI) calcd for C22H18N3O3S:
404.1069; found: 404.0636.
3-[5-(4-Toluyl)-1,3,4-oxadiazol-2-yl]-7-formyl-10-methylphenothiazine (11)
A mixture of 6 (1 g, 2.70 mmol), phosphorus oxychloride (2.74 ml, 29.5 mmol),
dimethylformamide (2.0 ml, 25.4 mmol) in chlorobenzene (5ml) was heated to 100 oC
for overnight. After cooling, ice water was added and the mixture was neutralized by
sat. NaHCO3 (aq). The mixture was allowed to stir for another half an hour to ensure
complete hydrolysis of the imine immediate which was then extracted by DCM for
several times. The combined organic phase was washed with sat. NaHCO3 (aq) and
then brine. The DCM solution was dried by anhydrous Mg2SO4 and concentrated in
vacuo to give the crude which was purified by flash column chromatography using
EA: Hexane: Triethylamine (1:1:2%) as eluent to offer 11 (552 mg, 51.2%) as an
22

ACCEPTED MANUSCRIPT
orange solid. mp 225.5-226.3 oC; δH (CDCl3) 7.97 (d, J = 8.4 Hz, 2 H), 7.91 (dd, J =
8.4 and 2.0 Hz, 1 H), 7.79 (d, J = 2.0 Hz, 1 H), 7.65 (dd, J = 8.4 and 2.0 Hz, 1 H),
7.58 (d, J = 1.6 Hz, 1 H), 7.30 (d, J = 8.0 Hz, 2 H), 6.89 (d, J = 8.4 Hz, 1 H), 6.87 (d,
J = 8.4 Hz, 1 H), 3.45 (s, 3 H), 2.41 (s, 3 H); δC (CDCl3) 189.0, 164.6, 163.4, 149.9,
146.8, 142.3, 131.8, 130.6, 129.8, 128.0, 126.8, 126.7, 125.3, 123.6, 123.3, 121.1,
119.3, 114.9, 114.3, 3.61, 21.7; HRMS (MALDI) calcd for C23H17N3O2S: 399.1041;
found: 399.1026.
3-[5-(4-Toluyl)-1,3,4-oxadiazol-2-yl]-7-vinyl-10-methylphenothiazine
(PO-Tol-
vinyl, 12)
To a suspension of potassium tert-butoxide (281 mg, 2.51 mmol) and methyl
triphenylphosphonium bromide (446 mg, 2.51 mmol) in dry THF (10 ml) was added
dropwise into a dry THF (10ml) solution of 11 (500 mg, 1.25 mmol) at room
temperature under stirring. The reaction mixture was allowed to stir for another half
an hour. Hexane (20 ml) was added and the whole mixture was filtered through a
short plug of silica, followed by washing with DCM for several times. The combined
DCM solution was concentrated in vacuo to give the crude product which was
purified by flash column chromatography with Hexane: EA: Triethylamine (4:1:2%)
as eluent to offer 12 (472 mg, 95.2%) as a green solid. mp 179.3-180.1 oC; δH (CDCl3)
7.99 (d, J = 8.4 Hz, 2 H), 7.90 (dd, J = 8.4 and 2.0 Hz, 1 H), 7.82 (d, J = 2.0 Hz, 1
H), 7.31 (d, J = 7.6 Hz, 2 H), 7.20-7.17 (m, 4 H), 6.58 (dd, J = 17.6 and 11.2 Hz, 1
23

ACCEPTED MANUSCRIPT
H), 5.62 (d, J = 17.6 Hz, 1 H), 5.16 (d, J = 11.2 Hz, 1 H), 3.40 (s, 3 H), 2.42 (s, 3 H);
δC (CDCl3) 164.4, 163.8, 148.2, 144.0, 142.1, 135.2, 133.0, 129.7, 126.8, 126.5,
125.9, 125.3, 124.7, 123.8, 122.6, 121.1, 118.0, 114.4, 114.1, 112.9, 35.7, 21.7;
HRMS (MALDI) calcd for C24H19N3OS: 397.1249; found: 397.1241.
Poly(PO-Tol) (13):
A solution of 12 (200 mg, 0.50 mmol) and catalytic AIBN (0.8 mg, 5 µmol) in toluene
(1 mL) was degassed by freeze-pump-thaw techniques for 5 cycles, then heated at
80oC under nitrogen for overnight. After cooling, the solution was added dropwise to
a stirring methanol and the precipitates thus formed were collected and further
purified by Soxhlet extraction using methanol as the extraction solvent for 2 days. The
resulting polymers were dried until constant weight (124.8 mg, 62.4%) as a light-
green powder. δH (CDCl3) 8.1-7.8 (br), 7.4-7.1 (br), 7.0-6.8 (br), 2.2-1.9 (br), 1.5-1.2
(br). Mn: 32,000 Da. PDI: 1.7. Anal. Calcd. for C24H21N3OS: C, 72.15%; H, 5.30%;
N, 10.52%. Found: C, 72.31%; H, 5.23%; N, 10.40%.
Acknowledgement
We are grateful to receive financial support for this work from the Hong Kong
Research Grants Council (HKBU 2105/06E).
References
1. Uoyama H, Goushi K, Shizu K, Nomura H, Adachi C. Highly efficient organic
light-emitting diodes from delayed fluorescence. Nature 2012;492:234-8.
2. Zhang Q, Li B, Huang S, Nomura H, Tanaka H, Adachi C. Efficient blue
organic light-emitting diodes employing thermally activated delayed
24

ACCEPTED MANUSCRIPT
fluorescence. Nat Photon 2014;8:326-32.
3. Kaji H, Suzuki H, Fukushima T, Shizu K, Suzuki K, Kubo S,
Komino T, Oiwa H, Suzuki F, Wakamiya A, Murata Y, Adachi C. Purely organic
electroluminescent material realizing 100% conversion from electricity to light.
Nat Comm 2015;6:8476.
4. Wong MY, Hedley GJ, Xie G, Kölln LS, Samuel IDW, Pertegás A, Bolink HJ,
Zysman-Colman E. Light-Emitting Electrochemical Cells and Solution-
Processed Organic Light-Emitting Diodes Using Small Molecule Organic
Thermally Activated Delayed Fluorescence Emitters. Chem Mater
2015;27:6535-42.
5. Qiu X, Xue S, Wu Y, Chen M, Sun Q, Yang W. Improving the
electroluminescence performance of donor–acceptor molecules by fine-tuning
the torsion angle and distance between donor and acceptor moieties. J Mater
Chem C 2016:4:5988-95.
6. Wong MY, Zysman-Colman E. Purely Organic Thermally Activated Delayed
Fluorescence Materials for Organic Light-Emitting Diodes. Adv Mater
2017:29:1605444.
7. Iqbal Z, Wu WQ, Huang ZS, Wang L, Kuang DB, Meier H, Cao D. Trilateral p-
conjugation extensions of phenothiazine-based dyes enhance the photovoltaic
performance of the dye-sensitized solar cells. Dyes Pigments 2016:124:63-71.
8. Huang ZS, Meier H, Cao D. Phenothiazine-based dyes for efficient dye-
sensitized solar cells. J Mater Chem C 2016:4:2404-26.
9. He X, Cao B, Hauger TC, Kang M, Gusarov S, Luber EJ, Buriak JM.
Donor−Acceptor Small Molecules for Organic Photovoltaics: Single-Atom
Substitution (Se or S). ACS Appl Mater Interfaces 2015;7:8188-99.
10. Li Z, Zhu Z, Chueh CC, Jo SB, Luo J, Jang SH, Jen AKY. Rational Design of
Dipolar Chromophore as an Efficient Dopant-Free Hole-Transporting Material
for Perovskite Solar Cells. J Am Chem Soc 2016;138:11833-11839.
11. Kularatne RS, Magurudeniya HD, Sista P, Biewer MC, Stefan MC. Donor-
Acceptor Semiconducting Polymers for Organic Solar Cells. J Polym Sci A
Polym Chem 2013;51:743-68.
12. Ellinger S, Graham KR, Shi P, Farley RT, Steckler TT, Brookins RN, Taranekar
P, Mei J, Padilha LA, Ensley TR, Hu H, Webster S, Hagan DJ, Stryland EWV,
Schanze KS, Reynolds JR, Donor-Acceptor-Donor-based π-Conjugated
Oligomers for Nonlinear Optics and Near-IR Emission. Chem Mater
2011;23:3805-17.
13. Chan CKM, Tao CH, Tam HL, Zhu N, Yam VWW, Cheah KW. Synthesis,
Characterization, Luminescence, and Non-linear Optical Properties of
Oxadiazole- and Truxene-Containing Platinum(II) Alkynyl Complexes with
Donor-Acceptor Functionalities. Inorg Chem 2009;48:2855-2864.
14. Konidena RK, Thomas KRJ, Kumar S, Wang YC, Li CJ, Jou CJ. Phenothiazine
Decorated Carbazoles: Effect of Substitution Pattern on the Optical and
Electroluminescent Characteristics. J Org Chem 2015;80:5812-23.
15. Wan Z, Jia C, Duan Y, Zhou L, Lin Y, Shi Y. Phenothiazine–triphenylamine
based organic dyes containing various conjugated linkers for efficient dye-
sensitized solar cells. J Mater Chem 2012;22:25140-7.
16. Rodrigues T, Santos CGD, Riposati A, Barbosa LRS, Mascio PD, Itri R,
Baptista MCS, Nascimento OR, Nantes IL. Photochemically Generated Stable
Cation Radical of Phenothiazine Aggregates in Mildly Acid Buffered Solutions.
J Phys Chem B 2006;110:12257-65.
25

ACCEPTED MANUSCRIPT
17. Oka H. Synthesis and through-bond spin interaction of stable 1,3-phenylene
linked poly(phenothiazine cation radical). J Mater Chem 2008;18:1927–34.
18. Lee J, Lee JI, Park MJ, Jung YK, Cho NS, Cho HJ, Hwang DH, Lee SK, Park
JH, Hong J, Chu HY, Shim HK. Phenothiazine-S,S-dioxide- and Fluorene-Based
Light-Emitting Polymers: Introduction of e--Deficient S,S-Dioxide into e--Rich
Phenothiazine. J Polym Sci Part A Polym Chem 2007;45:1236-46.
19. Yao L, Sun S, Xue S, Zhang S, Wu X, Zhang H, Pan Y, Gu C, Li F, Ma Y.
Aromatic S‑Heterocycle and Fluorene Derivatives as Solution-Processed Blue
Fluorescent Emitters: Structure-Property Relationships for Different Sulfur
Oxidation States. J Phys Chem C 2013;117:14189−96.
20. Liu Z, Shi E, Wan Y, Li N, Chen D, Xu Q, Li H, Lu J, Zhanga K, Wang L.
Effects of gradual oxidation of aromatic Sulphur-heterocycle derivatives on
multilevel memory data storage performance. J Mater Chem C 2015;3:2033-9.
21. Zhang Z, Wu Z, Sun J, Yao B, Zhang G, Xue P, Lu R. Mechanofluorochromic
properties of β-iminoenolate boron complexes tuned by the electronic effects of
terminal phenothiazine and phenothiazine-S,S-dioxide. J Mater Chem C
2015;3:4921-32.
22. Zhu L, Gu C, He Y, Wang G. Study on a highly selective fluorescent
chemosensor for Cu2+ and its direct sensing for proton based on 1,3,4-
oxadiazole. JOL 2014;153:439-45.
23. Zhou JA, Tang XL, Cheng J, Ju ZH, Yang LZ, Liu WS, Chena CY, Bai DC. An
1,3,4-oxadiazole-based OFF-ON fluorescent chemosensor for Zn2+ in
aqueous solution and imaging application in living cells. Dalton Trans
2012;41:10626-32.
24. Landis CA, Dhar BM, Lee T, Sarjeant A, Katz HE. Syntheses, Solid State
Structures, and Electrical Properties of Oxadiazole-Based Oligomers with
Perfluorinated Endgroups. J Phys Chem C 2008;112:7939-45.
25. Wang C, Jung GY, Batsanov AS, Bryce MR, Petty MC. New electron-
transporting materials for light emitting diodes: 1,3,4-oxadiazole-pyridine and
1,3,4-oxadiazole-pyrimidine hybrids. J Mater Chem 2002;12:173-180.
26. Liu R, Xu X, Peng J, Yao C, Wang J, Li L. Solution-processed oxadiazole-based
electron-transporting layer for white organic light-emitting diodes. RSC Adv
2015;5:36568-74.
27. Lee J, Shizu K, Tanaka H, Nomura H, YasudaT, Adachi C. Oxadiazole- and
triazole-based highly-efficient thermally activated delayed fluorescence emitters
for organic light-emitting diodes. J Mater Chem C 2013;1:4599-604.
28. Kulkarni AP, Tonzola CJ, Babel A, Jenekhe SA. Electron Transport Materials
for Organic Light-Emitting Diodes. Chem Mater 2004;16:4556-73.
29. Park YS, Choi J, Kim D, Lee B, Suh H, Kim JH. Synthesis, Optical, and
Electroluminescent Properties of Alternating Copolymer Based on
Phenothiazine and Fluorene with Oxadiazole Pendant. Mol Cryst Liq Cryst
2011:550:294-303.
30. Pan YZ, Wang YG, Liu JH, Sun LC. 10-Ethyl-3-(5-methyl-1,3,4-oxa-diazol-2-
yl)-10H-pheno-thia-zine. Acta Cryst. E 2012:68:o649.
31. Ahn GH, Je EG, Kim JA, Kim JG, Yoo JU, Lee CM. Phenothiazine derivative
as organic electroluminescent material and its preparing method. South Korea,
KR 2012 129 582 A.
32. Jenekhe SA, Lu L, Alam MM. New Conjugated Polymers with Donor-Acceptor
Architectures:ꢀSynthesis and Photophysics of Carbazole-Quinoline and
Phenothiazine-Quinoline Copolymers and Oligomers Exhibiting Large
26

ACCEPTED MANUSCRIPT
Intramolecular Charge Transfer. Macromolecules 2001;34:7315-24.
33. Kulkarni AP, Kong X, Jenekhe SA. High-Performance Organic Light-Emitting
Diodes Based on Intramolecular Charge-Transfer Emission from Donor-
Acceptor Molecules: Significance of Electron- Donor Strength and Molecular
Geometry. Adv. Funct. Mater. 2006, 16, 1057-66.
34. Hancock JM, Gifford AP, Zhu Y, Lou Y, Jenekhe, SA. n-Type Conjugated
Oligoquinoline and Oligoquinoxaline with Triphenylamine Endgroups:ꢀ
Efficient Ambipolar Light Emitters for Device Applications. Chem Mater
2006;18:4924-32.
35. Ishimatsu R, Matsunami S, Shizu K, Adachi C, Nakano K, Imato T. Solvent
Effect on Thermally Activated Delayed Fluorescence by 1,2,3,5-
Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene. J Phys Chem A 2013;117:5607-12.
36. Thomas KRJ, Lin JT, Tao YT, Chuen CH, Green and Yellow Electroluminescent
Dipolar Carbazole Derivatives:ꢀ Features and Benefits of Electron-Withdrawing
Segments. Chem Mater 2002;14:3852-9.
37. Saha S, Samanta A. Influence of the Structure of the Amino Group and Polarity
of the Medium on the Photophysical Behavior of 4-Amino-1,8-naphthalimide
Derivatives. J Phys Chem A 2002;106:4763-71.
38. Jia WL, Feng XD, Bai DR, Lu ZH, Wang S, Vamvounis G. Mes2B(p-4,4’-
biphenyl-NPh(1-naphthyl)):ꢀ A Multifunctional Molecule for Electroluminescent
Devices. Chem Mater 2005;17:164-70.
39. Islam A, Cheng CC, Chi SH, Lee SJ, Hela PG, Chen IC, Cheng CH.
Aminonaphthalic Anhydrides as Red-Emitting Materials:ꢀElectroluminescence,
Crystal Structure, and Photophysical Properties. J Phys Chem B 2005;109:5509-
17.
40. Smallwood IM. Handbook of Organic Solvent Properties, 1st ed.; Butterworth-
Heinemann: Oxford, 2012.
41. Duan,L, Hou L, Lee TW, Qiao J, Zhang D, Dong G, Wang, L Qiu Y. Solution
processable small molecules for organic light-emitting diodes. J Mater Chem
2010;20:6392-407.
42. O'Brien DF, Burrows PE, Forrest SR, Koene BE, Loy DE, Thompson ME. Hole
transporting materials with high glass transition temperatures for use in organic
light-emitting devices. Adv Mater 1998;10:1108-12.
43. Shen JY, Yang XL, Huang TH, Lin JT, Ke TH, Chen LY, Wu CC, Yeh MCP.
Ambipolar conductive 2,7-carbazole derivatives for electroluminescent devices.
Adv Funct Mater 2007;17:983-95.
44. Naito K, Miura A. Molecular design for nonpolymeric organic dye glasses with
thermal stability: relations between thermodynamic parameters and amorphous
properties. J Phys Chem 1993;97:6240-8.
45. Wang S, Oldham Jr. WJ, Hudack Jr. RA, Bazan GC. Synthesis, morphology, and
optical properties of tetrahedral oligo(phenylenevinylene) materials. J Am Chem
Soc 2000;122:5695-709.
46. Wang W, Lin T, Wang M, Liu TX, Ren L, Chen D, Huang S. Aggregation
Emission Properties of Oligomers Based on Tetraphenylethylene. J. Phys.
Chem. B 2010:114:5983-8.
47. Wong MY, La-Placa MG, Pertegas A, Bolink HJ, Zysman-Colman E. Deep-blue
thermally activated delayed fluorescence (TADF) emitters for light-emitting
electrochemical cells (LEECs). J. Mater. Chem. C 2017:5:1699-703.
48. Melhuish MH. Quantum efficiencies of fluorescence of organic substances:
effects of solvent and concentration of the fluorescent solute. J Phys Chem
27

ACCEPTED MANUSCRIPT
1961;65:229-35.
49. McNeil SK, Kelley SP, Beg C, Cook H, Rogers RD, Nikles DE. Cocrystals of
10-methylphenthiazine and 1,3-dinitrobenzene: implications for the optical
sensing of TNT-based explosives. ACS Appl Mater Interfaces 2013;5:7647-53.
28