Photophysical characterization of the 9,10-disubstituted anthracene chromophore and its applications in triplet-triplet annihilation photon upconversion

Article abstract of DOI:10.1039/c5tc02626a

Molecules based on anthracene are commonly used in applications such as OLEDs and triplet-triplet annihilation upconversion. In future design of blue emitting materials it is useful to know which part of the molecule can be altered in order to obtain new physical properties without losing the inherent optical properties. We have studied the effect of substitution of 9,10-substituted anthracenes. Eight anthracenes with aromatic phenyl and thiophene substituents were synthesised, containing both electron donating and accepting groups. The substitutions were found to affect the UV/Vis absorption only to a small extent, however the fluorescence properties were more affected with the thiophene substituents that decreased the fluorescence quantum yield from unity to <10%. DFT calculations confirm the minor change in absorption and indicate that the first and second triplet state energies are also unaffected. Finally the three most fluorescent derivatives 4-(10-phenylanthracene-9-yl)pyridine, 9-phenyl-10-(4-(trifluoromethyl)phenyl)anthracene and 4-(10-phenylanthracene-9-yl)benzonitrile were successfully utilized as annihilators in a triplet-triplet annihilation upconversion (TTA-UC) system employing platinum octaethylporphyrin as the sensitizer. The observed upconversion quantum yields, φ_UC, slightly exceeded that of the benchmark annihilator 9,10-diphenylanthracene (DPA).

Full text of DOI:10.1039/c5tc02626a

View Article Online
View Journal
Journal of
Materials Chemistry C
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: V. Gray, D. Dzebo,
A. Lundin, J. P. Alborzpour, M. Abrahamsson, B. Albinsson and K. Moth-Poulsen, J. Mater. Chem. C, 2015,
DOI: 10.1039/C5TC02626A.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/materialsC

Page 1 of 13
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC02626A
Photophysical
characterization
of
the
9,10-
disubstituted anthracene chromophore and ap-
plications in triplet-triplet annihilation photon
upconversion†
Victor Gray,a Damir Dzebo,a Angelica Lundin,a Jonathan Alborzpour,a Maria
Abrahamsson,a Bo Albinsson,a and Kasper Moth-Poulsen∗a
Molecules based on anthracene are commonly used in applications such as OLEDs and triplet-
triplet annihilation upconversion. In future design of blue emitting materials it is useful to know
what part of the molecule can be altered in order to obtain new physical properties without losing
the inherent optical properties. We have studied the effect of substitution of 9,10-substituted an-
thracenes. Eight anthracenes with aromatic phenyl and thiophene substituents were synthesised,
containing both electron donating and accepting groups. The substitutions were found to affect
the UV/Vis absorption only to a small extent, however the fluorescence properties were more af-
fected with the thiophene substituents that decreased the fluorescence quantum yield from unity
to <10%. DFT calculations confirm the minor change in absorption and indicate that the first and
second triplet state energies are also unaffected. Finally the three most fluorescent derivatives
4-(10-phenylanthracene-9-yl)pyridine, 9-phenyl-10-(4-(trifluoromethyl)phenyl)anthracene and 4-
(10-phenylanthracene-9-yl)benzonitrile were successfully utilized as annihilators in a triplet-triplet
annihilation upconversion (TTA-UC) system employing platinum octaethylporphyrin as the sen-
sitizer. Observed upconversion quantum yields, φUC, slightly exceeded that of the benchmark
annihilator 9,10-diphenylanthracene (DPA).
1 Introduction
cence quantum yield of about 70%23 and has been successfully
used in triplet-triplet annihilation systems previously by Parker24
Anthracene and its derivatives have played an important role
as an organic chromophore since its discovery in 1832 by Jean
B. A. Dumas and Auguste Laurent.1,2 Many dyes are based on
the anthracene structure and applications for these blue emit-
ting chromophores are plentiful in a variety of fields, from or-
ganic light emitting diodes (OLEDs)3–5 and fluorescent probes6–8
to organic scintillators9 and more recently photon-upconversion
through triplet-triplet annihilation.10–21
and more recently by McCusker and Castellano.25 For many ap-
plications it is desirable with a high emission yield and 9,10-
substituted anthracenes are potential candidates. As the substi-
tutions also influence other important factors, such as solubility,
crystal structure, exciplex formation, surface affinity and spectral
characteristics there can be multiple purposes for the choice of
substituents. Bulky substituents, such as phenyl groups, are also
known to hamper the [4+4] photocycloaddition that anthracene
and 9,10-dimethylanthracene undergoes at high concentrations
when irradiated.23,24,26
Unsubstituted anthracene has a fluorescence quantum yield of
about 30%, a consequence of the high intersystem crossing rate
and a triplet yield of proximately 70%.22 Substituting anthracene
at the 9- and 10-positions can drastically alter the probability
of these transitions, e.g 9,10-dimethylanthracene has a fluores-
Photon upconversion is the process of generating high energy
photons from two, or more low energy photons. Through triplet-
triplet annihilation (TTA) this can be achieved with incoherent
low intensity light such as sunlight.10,13,27–32 Thus, TTA photon
upconversion has gained a lot of interest as a way to improve
the efficiency of solar energy applications33,34 such as photo-
voltaics,35–42 photoelectrochemical15,43 and solar driven photo-
chemical reactions26,44 by utilizing sub-bandgap photons. TTA
a
Chalmers University of Technology, Gothenburg, Sweden. E-mail: kasper.moth-
poulsen@chalmers.se
† Electronic Supplementary Information (ESI) available: Absorption spectra, Tran-
sient absorption spectra, Stern-Vomer plot for PdOEP and NMR spectra can be found
in ESI. See DOI: 10.1039/b000000x/
1–12 | 1

Journal of Materials Chemistry C
Page 2 of 13
View Article Online
DOI: 10.1039/C5TC02626A
N
1A*
1A*
1
2
3
5.
2.
2.
1S*
1S*
3.
3.
3S*
3S*
4.
3A*
3A*
CF3
N
O
1.
1.
5
4
6
1A
1S
1A
1S
S
S
S
S
Fig. 1 Jablonski diagram explaining the triplet-triplet annihilation
upconversion process. First a sensitizer absorbs a low energy photon
(1) and rapidly populates its first triplet excited state after intersystem
crossing (ISC) from the singlet state (2). The triplet energy can then be
transferred to an annihilator species through a triplet energy transfer
(TET) process (3) generating one triplet excited annihilator molecule.
When two triplet excited annihilator molecules come together they can
undergo triplet-triplet annihilation (4) generating one singlet excited
annihilator which can deactivate to its ground state by emitting a photon
(5).
CF3
8
7
9
N
O
CF3
N
M
N
N
10
MOEP
photon upconversion, schematically described in figure 1, gener-
ally occurs in a bimolecular system, consisting of a triplet sensi-
tizer (S), typically metalloporphyrins, and an annihilator species
(A), commonly polyaromatic molecules. The process was first de-
scribed in the 1960s by Parker and Hatchard45–47 and consists
of a series of events. First a low energy photon is absorbed by a
sensitizer in its ground state (1S) which readily undergoes inter-
system crossing (ISC) forming its first excited triplet state (3S*).
Subsequently the triplet state of the annihilator (3A*) is popu-
lated through a triplet-energy transfer (TET) process from the
sensitizer. Two triplet-excited annihilators can then interact and
undergo triplet-triplet annihilation (TTA), which can result in the
formation of one singlet excited annihilator (1A*) and one anni-
hilator in the ground state (1A). The excited singlet can subse-
quently relax to the ground state through fluorescence, emitting
a photon of higher frequency than the ones initially absorbed. In
reality one TTA event does not necessarily form one singlet state
if triplet and quintet states are energetically accessible, and spin-
statistics was first assumed to limit the TTA process to efficiencies
below 1/9. However experimental data has disproven this limit
with observed efficiencies well above 1/9.15,48
One of the most efficient upconversion sensitizer-annihilator
pairs is DPA, 1 (figure 2) and Pd or Pt octaethylporphyrin, with
an upconversion quantum yield up to 18%.15 Lately some promis-
ing attempts to modify 1 has been made in order to facilitate and
achieve TTA-UC in different matrices.17,20,49,50 However no de-
tailed study of how these modifications alter the photophysical
properties of the chromophore 1 has been done. With the aim of
identifying structure/property relations for 9,10-substituted an-
thracenes and revealing design parameters for future TTA-UC
materials we here present the synthesis and study of photo-
physical properties of eight 9,10-disubstituted anthracene deriva-
tives (figure 2). To complement the experimental measure-
M = Pt, Pd
Fig. 2 Structures of investigated 9,10-substituted anthracenes and the
triplet sensitizers Platinum and Palladium octaethylporphyrin
ments DFT calculations of the position of singlet and triplet ex-
cited states were performed in order to determine the S-T en-
ergy level spacing. Both electron withdrawing and electron do-
nating substituents have been chosen. We further demonstrate
the use of the most promising derivatives as annihilators in the
triplet-triplet annihilation based upconversion, using platinum
octaethylporphyrin (PtOEP) as the sensitizer. The derivatives are
compared to the well known 9,10-diphenylanthracene (1) and
9,10-dimethylanthracene (2) chromophores.
2 Experimental method
2.1 Instrumentation and Optical Measurements
Steady-state absorption was recorded on a Cary 4000 Spectropho-
tometer and steady state fluorescence measurements were car-
ried out on a Spex Flurolog 3 spectrofluorimeter (JY Horiba).
Fluorescence lifetimes were determined on a time correlated sin-
gle photon counting (TCSPC) setup using PicoQuant laser diodes
(377 nm) and a PMT detector (10000 counts, 4096 channels).
Nanosecond transient absorptions measurements were performed
on home built system with a Surelite Continuum Nd:YAG laser
equipped with an OPO generating a ∼10 ns pump beam.
A
quartz-halogen lamp with a monochromator was used as the
probe light and a monochromator together with a 5 stage PMT
coupled to an oscilloscope was used for recording the transient.
All photophysical measurements were carried out in toluene us-
ing quartz cuvettes except for samples used in the upconversion
intensity study which were permanently sealed in Pyrex test-
2 |
1–12

Page 3 of 13
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC02626A
tubes after degassing following a freeze-pump-thaw procedure
together with 201 mg (0.98 mmol) of 4-pyridine boronic acid
pinacole ester and 27 mg (0.02 mmol, 2 mol%) of Pd(PPh3)4.
The atmosphere was exchanged to N2 and 4.9 mL degassed THF,
2.5 mL K2CO3 (aq, 2 M, N2 purged) and a drop of phasetrans-
fer catalyst Aliquat 336 was added. The mixture was heated to
reflux for 76 h. The crude mixture was evaporated to dryness
and then loaded on a manually packed silica column, eluted with
DCM until the first fraction was obtained, then DCM with 1%
MeOH (Rf = 0.57, 2% MeOH in DCM) to yield light yellow crys-
tals (219 mg, 0.66 mmol, 67%). Mp=280.7°C. Elem. Anal.: Calc.
(C25H17N): C: 90.60% H: 5.17% N: 4.23%, Found: C: 90.56%
H: 5.19% N: 4.22%. FT-IR (KBr) ν(cm−1) = 3429 (bs), 3061 (m),
2922 (m), 2851 (m), 2359 (w), 1941 (w), 1809(w), 1704 (w)
1646 (w), 1592 (s), 1538 (m) 1519 (w) 1495 (m) 1438 (s) 1390
(s) 1324 (m), 1254 (m) 1212 (m), 1167 (m), 1145 (m), 1118
(m), 1068 (m), 1025 (s), 989 (m) 945 (m), 915 (w), 901 (w),
877 (w), 849 (w), 817 (m), 768 (s), 703 (s), 673 m), 651 (s),
610 (s) 527 (s) 427 (w). H1-NMR (400 MHz, CDCl3)δ = 8.88
(dd, J1 =4.3 Hz, J2 =1.6 Hz, 2H), 7.74-7.70 (m, 2H), 7.64-7.55
(m, 5H), 7.49-7.46 (m, 4H), 7.40-7.33 (m, 4H) ppm. C13-NMR
(400 MHz, CDCl3) δ = 150.05, 147.74, 138.66, 138.21, 131.16,
129.76, 129.06, 128.46, 127.64, 127.21, 126.58, 126.00, 125.68,
125.1 ppm. MALDI-TOF (m/z): Found: 330.9 Calc: 331.14
described in ESI†. Samples for Stern-Volmer quenching studies
and nanosecond transient absorption studies were degassed by
stirring in a glovebox from Innovative Technologies (<0.1 ppm
oxygen level) under nitrogen atmosphere for at least 48 h.
Fluorescence quantum yields were determined by relative acti-
nometry employing 1 as the standard using deaerated dilute so-
lutions and comparative spectra were corrected for absorbance.
Upconversion quantum yields were determined relative to zinc
octaethyl porphyrin51 using a 532 nm green laser-pointer (33.8
mW, 0.0573 cm2) as the light source and a graduated neutral
density filter to vary the intensity. Solubility experiments were
carried out by saturating a solution of toluene with each deriva-
tive and then filtering of the supernant with a syringe filter before
recording absorption spectra to monitor the amount of dissolved
species.
1 was purchased from Sigma-Aldrich, PtOEP and PdOEP were
purchased from PorphyChem and all were used as received. 2
was a kind gift from the late Prof. Hans-Dieter Becker and pu-
rity was confirmed by H1-NMR spectroscopy prior to use. Spec-
troscopy and GC grade toluene was used for all measurements.
Degassed and dry toluene was obtained from a M-Braun solvent
drying system. NMR was run on a 400 MHz Varian NMR and IR
was run either neat or in KBr pellets using an Perkin Elmer ATR-
FTIR or Perkin Elmer FTIR respectively. Column chromatography
was carried out using a Biotage Flash Column Chromatography
system with Biotage prepacked SNAP columns if not stated other-
wise. Melting points were determined using an automatic Mettler
Toledo MP70 melting point apparatus.
Preparation
of
9-phenyl-10-(4-(trifluoromethyl)phenyl)-
anthracene, 4: The title compound was synthesized as follows;
237 mg (0.7 mmol) of 9-bromo-10-phenylanthracene was
added to a reaction vessel together with 290 mg (1.5 mmol) of
4-(trifluoromethyl)phenyl boronic acid and 75 mg (0.06 mmol,
9 mol%) of Pd(PPh3)4. The atmosphere was exchanged to N2
and 30 mL degassed toluene, 28 mL degassed THF and 5 mL
Na2CO3 (aq, 2 M, N2 purged) was added. The mixture was
heated to reflux over night. The crude mixture was extracted
with petroleum ether, washed with brine and dried with Na2SO4.
The crude product was purified by column chromatography
(1-8% DCM in hexane, Rf = 0.26, 4% DCM in hexane) to yield a
light yellow powder (232 mg, 0.58 mmol, 83%). Mp =254.7°C.
Elem. Anal.: Calc. (C27H17F3): C: 81.39% H: 4.30% F: 14.31%,
Found: C: 81.08% H: 4.36% F: 14.27%. FT-IR (neat, ATR)
ν(cm−1) = 3061 (bw) 2820 (w) 1615 (m), 1494 (w), 1440 (m),
1402 (m) 1393 (m), 1324 (s) 1161 (s), 1117 (s), 1020 (m), 942
(m), 835 (m), 770 (s), 760 (s), 700 (m), 666 (s), 624 (m), 610
(s), 515 (m), 440 (m), 421 (m). H1-NMR (400 MHz, CDCl3)
δ = 7.88 (d, J=8.08 Hz, 2H ), 7.72-7.70 (m, 2H), 7.64-7.56
(m, 6H), 7.49-7.47 (m, 2H), 7.38-7.33 (m, 4H) ppm. C13-NMR
(400 MHz,CDCl3) δ = 143.15, 138.78, 137.87, 135.16, 131.76,
131.20, 129.98, 129.80, 129.66, 129.60, 128.44, 127.58,
127.13, 126.32, 125.46, 125.41, 125.11 ppm. F19-NMR (400
MHz, CDCl3) δ = -62.38 ppm. MALDI-TOF (m/z): Found: 398.0
Calc: 398.1
2.2 Synthesis
Phenyl-substitutents where coupled to the anthracene core
by Suzuki-Miyaura cross coupling procedures (figure 3) and
thiophene-substitutents by Stille cross coupling procedures (fig-
ure 3). 9-Bromo-10-phenylanthracene was synthesized according
to literature52
.
i or ii
iii
R
Br
R1
R2
R3
R2
iv
3: R1 = Ph, R2 = Pyr
9: R2 = Thiophene, R3 = Ph-CF3
10: R2 = Ph-OMe, R3 = Ph-CF3
R = Ph or Br
4: R1 = Ph, R2 = Ph-CF3
5: R1 = Ph, R2 = Ph-CN
6: R1 = Ph, R2 = Ph-OMe
7: R1 = Ph, R2 = Thiophene
8: R1 = R2 = Thiophene
11: R1 = Br, R2 = Thiophene
12: R1 = Br, R2 = Ph-OMe
Fig. 3 Synthesis of 9,10-disubstituted anthracenes. i) Suzuki coupling;
Arylboronic acid, Pd(PPh3)4, Na2CO3 (2 M aq), THF, Toluene, Reflux, ii)
Stille coupling; 2-Bu3Sn-thiophene, Pd2(dba)3, tri-o-tolylphosphine, THF,
Reflux, iii) CF3-Ph-B(OR)2, Pd(PPh3)4, iv) Toluene, THF, Na2CO3 (2 M,
aq), Reflux, 18 h
Preparation of 4-(10-phenylanthracene-9-yl)benzonitrile , 5:
The title compound was synthesized as follows; 350 mg (1.05
mmol) of 9-bromo-10-phenylanthracene was added to a reac-
tion vessel together with 230 mg (1.58 mmol) of 4-cyanophenyl
boronic acid and 60 mg (0.05 mmol, 9 mol%) of Pd(PPh3)4. The
atmosphere was exchanged to N2 and 9 mL degassed toluene, 2
mL ethanol and 2 mL K2CO3 (aq, 4.9 M, N2 purged) was added
Preparation of 4-(10-phenylanthracene-9-yl)pyridine, 3: The ti-
tle compound was synthesized as follows; 330 mg (0.99 mmol)
of 9-bromo-10-phenylanthracene was added to a reaction vessel
1–12 | 3

Journal of Materials Chemistry C
Page 4 of 13
View Article Online
DOI: 10.1039/C5TC02626A
and the reaction was purged with N2 for 30 minutes. The mix-
ture was then heated to reflux for 24 h. After cooling to room
temperature the crude mixture was extracted with DCM, washed
with brine and dried with Na2SO4. The crude product was pu-
rified by column chromatography, eluted with hexane until the
first fraction was collected, thereafter DCM (Rf = 0.57 in DCM)
to yield a light yellow powder (313 mg, 0.88 mmol, 84%). Mp
= 281.6°C. Elem. Anal.: Calc. (C27H17N): C: 91.24% H: 4.82%
N: 3.94%, Found: C: 91.24% H: 4.83% N: 3.95%. FT-IR (neat,
ATR) ν(cm−1) = 3056 (bw), 2230 (m), 1934 (bw), 1815 (w),
1603 (m), 1497 (m), 1438 (m), 1390 (m), 1271 (w), 1253 (w),
1190 (w), 1106 (w), 1069 (w), 1027 (m), 941 (m), 896 (w),
880 (w), 849 (m), 834 (m), 793 (w), 764 (s), 734 (w), 700
(s), 669 (s), 641 (m), 611 (s), 555 (s), 521 (w), 501(w), 421
(m). H1-NMR (400 MHz, CDCl3) δ = 7.94-7.91 (dt, J1 =8.4 Hz,
J2 =1.6 Hz, 2H), 7.73-7.69 (m, 2H), 7.63-7.61 (m, 2H), 7.60-7.52
(m, 4H), 7.48-7.46 (m, 2H), 7.39-7.33 (m, 4H) ppm. C13-NMR
(400 MHz, CDCl3) δ = 144.53, 138.63, 138.26, 134.47, 132.29,
131.15, 129.77, 129.36, 128.46, 127.65, 127.24, 125.98, 125.69,
125.17, 118.90, 111.60, 31.37 ppm. MALDI-TOF (m/z): Found:
354.8 Calc: 355.14
(tertbutylstannyl)-thiophene was added. The reaction mixture
was heated to reflux over night. The crude mixture was ex-
tracted with DCM, washed with brine and dried over Na2SO4.
The crude product was filtered over a plug of silica eluted with
toluene and evaporated to dryness. The pale white crystals were
washed with hexane to yield 151 mg (0.45 mmol, 60% ) of the
title compound. Mp = 197.0°C. Elem. Anal.: Calc. (C24H16S):
C: 85.68%, H: 4.79% S: 9.53%, Found: C: 85.58% H: 4.81%,
S: 9.45%. FT-IR (KBr) ν(cm−1) = 3060 (bm), 1947 (w), 1806
(w), 1708 (w), 1598 (w), 1518 (w), 1438 (m), 1377 (m), 1389
(m), 1286 (w), 1222 (m), 1161 (w), 1112 (w), 1070 (w), 1027
(m), 931 (m), 834 (m), 765 (s), 741 (m), 702 (m), 692 (s), 670
(m), 651 (s), 632 (w), 611 (s), 596 (w), 487 (w), 511 (m), 487
(w), 446 (w), 416 (m) H1-NMR (400 MHz, CDCl3) δ = 7.90-
7.88 (m, 2H), 7.69-7.67 (m, 2H), 7.63 (dd, J1 = 1.2 Hz, J2
5.2 Hz, 1H), 7.61-7.58, (m, 2H) 7.57-7.54 (m, 1H), 7.48-7.45
(m, 2H), 7.42-7.36 (m, 3H), 7.34-7.32 (m, 2H), 7.23 (dd, J1
=
=
1.2 Hz, J2 = 3.4 Hz, 1H) ppm. C13-NMR (400 MHz, CDCl3) δ =
139.23, 138.82, 138.50, 131.55, 131.16, 129.78, 129.46, 128.73,
128.40, 127.55, 127.16, 126.94, 126.68, 126.66, 125.51, 125.11
ppm. MALDI-TOF (m/z): Found: 335.8 Calc: 336.1
Preparation of 9-(4-methoxyphenyl)-10-phenylanthracene, 6:
The title compound was synthesized as follows; 195 mg (0.59
mmol) of 9-bromo-10-phenylanthracene was added to a reaction
vessel together with 205 mg (1.35 mmol) of 4-methoxyphenyl
boronic acid and 64 mg (0.05 mmol, 9 mol%) of Pd(PPh3)4. The
atmosphere was exchanged to N2 and 9 mL degassed toluene, 9
mL degassed THF and 4.5 mL Na2CO3 (aq, 2 M, N2 purged) was
added. The mixture was heated to reflux for 43 h. The crude
mixture was extracted with hexane, washed with brine and dried
with Na2SO4. The crude product was filtered over a silica plug
eluted with 16% DCM in hexane (Rf = 0.20). The yellow crys-
tals were recrystalized from toluene to yield light yellow crystals
(151 mg, 0.42 mmol, 70%). Mp = 233.6°C. Elem. Anal.: Calc.
(C27H20O): C: 89.97% H: 5.59% O: 4.44%, Found: C: 89.98% H:
5.62% O: 4.30%. FT-IR (neat, ATR) ν(cm−1) = 3068 (w), 3041
(w), 2997 (m), 2961 (m), 2839 (w), 1955 (bw), 1888 (bw), 1815
(w), 1708 (w), 1636 (w), 1607 (m), 1573 (m), 1512 (s), 1496
(m), 1461 (m), 1439 (m), 1408 (w), 1390 (m), 1369 (w), 1303
(w), 1284 (m), 1241 (s), 1181 (m), 1104 (m), 1070 (m), 1027
(s), 941 (m), 915 (w), 877 (w), 848 (m), 830 (s), 791 (w), 770
(s), 755 (s), 731 (w), 714 (w), 704 (s), 665 (s), 638 (m), 627
(m), 611 (s), 578 (m), 534 (m), 498 (w), 418 (m). H1-NMR
(400 MHz, CDCl3) δ = 7.77-7.73 (m, 2H), 7.70-7.67 (m, 2H),
7.63-7.52 (m, 3H), 7.49-7.47 (m, 2H), 7.42-7.38 (m, 2H), 7.36-
7.30 (m, 2H), 7.17-7.13 (m, 2H), 3.97 (s, 3H) ppm. C13-NMR
(400 MHz, CDCl3) δ = 218.85, 159.00, 139.11, 136.91, 136.89,
132.36, 131.31, 131.08, 130.19, 129.89, 128.37, 127.41, 127.02,
126.93, 124.93, 124.88, 55.38 ppm. MALDI-TOF (m/z): Found:
360.1 Calc: 360.2
Preparation of 9,10-di(thiophene-2-yl)anthracene, 8: The title
compound was synthesized as follows; 500 mg (1.49 mmol) of
9,10-dibromoanthracene was added to a dry reaction vessel with
the catalyst Pd2(dba)3 (56 mg, 0.06 mmol, 2 mol%) and the lig-
and tri-o-tolyl phosphine (75 mg, 0.24 mmol). Under nitrogen
20 mL of dry THF and 1.3 mL (4.1 mmol) 2-(tertbutylstannyl)-
thiophene was added. The reaction mixture was heated to reflux
over night. The crude mixture was extracted with DCM, washed
with brine and dried over Na2SO4. The crude product was fil-
tered over silica and then recrystallized from toluene and washed
with hexane to yield 409 mg (1.2 mmol, 80% ) yellow crystals.
Mp = 246.1°C. Elem. Anal.: Calc. (C22H14S2): C: 77.16%, H:
4.12% S: 18.72%, Found: C: 77.26% H: 4.00%, S: 18.66%. FT-
IR (KBr) ν(cm−1) = 3102 (w), 3058 (w), 2921 (m), 2851 (m),
1789 (w), 1717 (w), 1529 (w), 1448 (w), 1435 (m), 1372 (m),
1328 (m), 1258 (w), 1221 (m), 1173 (w), 1146 (w), 1136 (w),
1101 (m), 1036 (m), 1025 (m), 957 (w), 904 (m), 848 (m), 817
(s), 767 (s), 741 (m), 692 (s), 670 (s), 652 (m), 643 (m), 612
(m), 602 (m), 510 (m), 490 (w), 415 (m). H1-NMR (400 MHz,
CDCl3) δ = 7.89-7.85 (m, 4H), 7.63 (dd, J1 = 1.2 Hz, J2 = 5.2
Hz, 2H), 7.43-7.39 (m, 4H), 7.32 (dd, J1 = 3.4 Hz, J2 = 5.2 Hz,
2H) 7.22 (dd, J1 = 1.2 Hz, J2 = 3.4 Hz, 2H) ppm. C13-NMR
(400 MHz, CDCl3) δ = 138.88, 131.42, 130.21, 129.51, 127.17,
126.79, 126.65, 125.64, 77.32, 77.00, 76.68.ppm. MALDI-TOF
(m/z): Found: 341.7 Calc: 342.05
Preparation of 2-(10-(4-trifluoromethyl)phenyl)anthracen-9-yl)-
thiophene, 9: The title compound was prepared as follows; 188
mg (2.7 mmol) of 2-(10-bromoanthracene-9-yl)thiophene was
added to a reaction vessel together with 232 mg (1.5 mmol) 4-
(trifluoro)phenyl boronic acid and 62 mg (0.05 mmol, 9 mol%)
of Pd(PPh3)4. The atmosphere was exchanged to N2 and 5 mL
degassed toluene, 5 mL degassed THF and 4 mL Na2CO3 (aq,
2 M, N2 purged) was added. The mixture was heated to reflux
for 18 h, and 39 mg (0.03 mmol) Pd(PPh3)4 was added and the
mixture was heated to reflux for another 8 h. The crude mix-
Preparation of 2-(10-phenylanthracen-9-yl)thiophene, 7: The ti-
tle compound was synthesized as follows; 250 mg (0.75 mmol) of
9-bromo-10-phenylanthracene was added to a dry reaction ves-
sel with the catalyst Pd2(dba)3 (17 mg, 0.02 mmol, 2.4 mol%)
and the ligand tri-o-tolyl phosphine (28 mg, 0.09 mmol). Un-
der nitrogen 7.5 mL of dry THF and 0.26 mL (0.83 mmol) 2-
4 |
1–12

Page 5 of 13
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC02626A
ture was extracted with DCM, washed with brine and dried over
9,10-dibromoanthracene was added to a dry reaction vessel with
the catalyst Pd2(dba)3, 23 mg (0.025 mmol, 1 mol%) and the
ligand tri-o-tolyl phosphine 34 mg ( 0.11 mmol). Under nitrogen
24 mL of dry THF and 0.38 mL (1.2 mmol) 2-(tertbutylstannyl)-
thiophene was added. The reaction mixture was heated to reflux
over night. The crude mixture was extracted with DCM, washed
with brine and dried over Na2SO4. The crude product was puri-
fied by column chromatography, eluted with hexane (Rf = 0.32)
to yield 188 mg (0.55 mmol, 46% ) of yellow crystals. H1-NMR
(400 MHz, CDCl3) δ = 8.59 (d, J = 8.9 Hz, 2H), 7.83 (d, J =8
.9 Hz, 2H), 7.63-7.58 (m, 1H), 7.46-7.42 (m, 1H), 7.32-7.28 (m,
1H), 7.20-7.17 (m ,1H) ppm. Spectroscopic data was in agree-
ment with that reported previously.53
Na2SO4. The crude product was purified by column chromatogra-
phy, eluted with a gradient of 2-16% DCM in hexane (Rf = 0.47,
20% DCM in hexane) yielding light yellow crystals, 142 mg (0.35
mmol, 64%). Mp = 261.4°C. Elem. Anal.: Calc. (C25H15F3S):
C: 74.24% H: 3.74% F: 14.09% S: 7.93%, Found: C: 74.68% H:
4.01%, F: 13.41%, S: 6.54%. FT-IR (KBr)ν(cm−1) = 3068 (bw),
2878 (w), 1929 (w), 1805 (bw), 1712 (bw), 1614 (m), 1574
(w), 1519 (w), 1439 (m), 1404 (m), 1380 (m), 1319 (s), 1222
(m), 1185 (m), 1160 (s), 1141 (s), 1113 (s), 1104 (s), 1065 (s),
1020 (m), 956 (w), 932 (m), 860 (w), 850 (w), 836 (m), 825
(s), 764 (s), 748 (m), 741 (m), 708 (w), 692 (s), 674 (m), 659
(s), 634 (m), 615 (s), 596 (m), 511 (m), 494 (w), 464 (w), 442
(m), 417 (m). H1-NMR (400 MHz, CDCl3) δ = 7.90 (m, 4H),
7.65 (dd, J1 = 1.2 Hz, J2 = 5.2 Hz, 1 H) , 7.62-7.56 (m, 4H),
7.44-7.33 (m, 5H), 7.24 (dd, J1 = 1.2 Hz, J2 = 3.4 Hz, 1H) ppm.
C13-NMR (400 MHz, CDCl3) δ = 142.89, 138.86, 136.53, 131.62,
131.48, 130.10, 129.77, 129.58, 129.53, 127.20, 126.85, 126.82,
126.31, 125.64, 125.60, 125.47, 125.43, 109.99 ppm. F19-NMR
(400 MHz, CDCl3) δ = -62.39 ppm. MALDI-TOF (m/z): Found:
403.7 Calc: 404.1
Preparation of 9-(4-methoxyphenyl)-10-(4-(trifluoromethyl)-
phenyl)anthracene, 10: The title compound was synthesized
as follows; 125 mg (0.34 mmol) of 9-bromo-10-(4-methoxy-
phenyl)anthracene was added to a reaction vessel together with
140 mg (0.74 mmol) of 4-(trifluoro)phenyl boronic acid and 39
mg (0.03 mmol, 9 mol%) of Pd(PPh3)4. The atmosphere was ex-
changed to N2 and 15 mL degassed toluene, 15 mL degassed THF
and 2.5 mL Na2CO3 (aq, 2 M, N2 purged) was added. The mix-
ture was heated to reflux for 18 h, then the reaction was purged
with N2 for 40 min where-after 40 mg (0.03 mmol) Pd(PPh3)4
and 140 mg 0.74 mmol) of 4-(trifluoro)phenyl boronic acid was
added. The reaction was then heated to reflux for another 24 h.
The crude mixture was extracted with petroleum ether, washed
with brine and dried with Na2SO4. The crude product was pu-
Preparation of 9-bromo-10-(4-methoxyphenyl)anthracene, 12:
The title compound was synthesized as follows; 200 mg (0.60
mmol) of 9,10-dibromoanthracene was added to a reaction vessel
together with 480 mg (3.15 mmol) of 4-methoxyphenyl boronic
acid and 100 mg (0.09 mmol, 7.5 mol%) of Pd(PPh3)4. The
atmosphere was exchanged to N2 and 25 mL degassed toluene,
25 mL degassed THF and 10 mL Na2CO3 (aq, 2 M, N2 purged)
was added. The mixture was heated to reflux overnight. The
crude mixture was extracted with petroleum ether, washed with
brine and dried with Na2SO4. The crude product was purified
by column chromatography (4-32% DCM in hexane, Rf = 0.29,
16% DCM in hexane) to yield light yellow crystals (125 mg, 0.34
mmol, 58%). H1-NMR (400 MHz, CDCl3) δ = 8.60 (d, J = 9.5
Hz, 2H), 7.70 (d, J = 8.2 Hz, 2H), 7.60-7.56 (m, 2H), 7.39-7.36
(m, 2H), 7.31 (d, J =7.5 Hz, 2H), 7.12 (d, J =7.6 Hz, 2H), 3.95
(s, 3H) ppm. Spectroscopic data are in good agreement with
those reported previously.54
2.3 Calculations
The popular hybrid functional B3LYP55,56 was used in connec-
tion with a triple-zeta basis set, 6-311+G(d,p)57–59 as imple-
mented in Gaussian 09.60 All structures were fully optimized and
consequently confirmed as local minima by calculation of second
derivatives. Excited state calculations were performed using the
time-dependent DFT method.61,62
rified by column chromatography (3-30% DCM in hexane, Rf
=
0.31, 15% DCM in hexane) to yield light yellow crystals (113
mg, 0.26 mmol, 77%). Mp = 305.7°C. Elem. Anal.: Calc.
(C27H19F3O): C: 78.4% H: 4.47% F: 13.30%, Found: C: 77.13%,
H: 4.54%, F: 13.30%. FT-IR (KBr) ν(cm−1) = 3065 (bw), 2953
(w), 1939 (bw), 1817 (bw), 1613 (m), 1605 (m), 1574 (w), 1510
(m), 1460 (m), 1440 (m), 1403 (m), 1392 (m), 1367 (w), 1321
(s), 1286 (m), 1242 (m), 1175 (m), 1158 (s), 1120 (s), 1104 (s),
1065 (s), 1036 (m), 1021 (m), 942 (m), 883 (w), 866 (w), 848
(m), 826 (s), 818 (m), 708 (w), 771 (s), 751 (s), 730 (w), 672
(s), 644 (w), 633 (m), 621 (w), 610 (m), 591 (w), 577 (m), 533
(m), 506 (w), 430 (m), 421 (m). H1-NMR (400 MHz, CDCl3) δ
= 7.88 (d, J = 7.9 Hz, 2H), 7.79-7.75 (m, 2H), 7.62 (d, J= 7.8 Hz
2H), 7.60-7.56 (m, 2H), 7.41-7.33 (m, 6H), 7.15 (dt, J1 = 8.7 Hz,
J2 = 2.8 Hz, 2H), 3.97 (s, 3H) ppm. C13-NMR (400 MHz, CDCl3)
δ = 159.10, 137.69, 134.99, 132.28, 131.76, 130.78, 130.14,
129.63, 127.22, 126.31, 125.43, 125.40, 125.02, 113.90, 55.39
ppm. F19-NMR (400 MHz, CDCl3) δ = -62.36 ppm. MALDI-TOF
(m/z): Found: 428.0 Calc: 428.14
3 Results and Discussion
3.1 Synthesis
The commercially available 9,10-dibromoanthracene and 9-
phenylanthracene were used as starting material for Suzuki-
Miyaura (S-M) and Stille cross-coupling reactions. The Stille
cross-coupling procedure in dry THF was preferred for the
thiophene-anthracene coupling as it proceeded smoothly and re-
sulted in higher yields (46-80%) than the corresponding S-M pro-
cedures first attempted (<10%). The phenyl-substituents were
successfully coupled using S-M cross-coupling procedures (58-
84%). A system of THF/Toluene/Na2CO3(aq)53 was generally
used, except for the nitrogen containing phenyl groups which
gave higher yields when carried out in a THF/K2CO3(aq) mix-
ture. It was also observed that reducing the amount of solvent to
half or less in the S-M procedure compared to what was initially
used53 resulted in higher yields (from 35% to 70%).
Preparation of 2-(10-bromoanthracene-9-yl)thiophene, 11: The
title compound was synthesized as follows; 908 mg (2.7 mmol) of
1–12 | 5

Journal of Materials Chemistry C
Page 6 of 13
View Article Online
DOI: 10.1039/C5TC02626A
Fig. 4 a) Molar absorptivity of the representative compounds 1 (—), 3 (—), 4 (—),5 (—), 8 (—) and b) Relative Fluorescence intensity of synthesized
anthracene derivatives compared to 1 (—), 3 (—), 4 (—), 5 (—), 6 (—), 7 (—), 8 (—), 9 (—) and 10 (—), spectra are corrected for absorbance.
3.2 Photophysical characterization
tected for the derivatives when directly excited at 355 nm. There-
fore samples of 1-10(∼70µM) were prepared with 1µM PtOEP
and were pumped at 532 nm using a fraction of the frequency
doubled fundamental pump beam. All samples were degassed
in a glove-box prior to measuring. The triplet decays were fit to
equation 1 which takes into account the contribution of triplet-
triplet annihilation which can occur at high triplet state concen-
trations48,65,66 (figures S12-S20†):
Photophysical properties of the studied derivatives are presented
in table 1. Absorption spectrum and molar absorptivities of five
representative anthracene derivatives are presented in figure 4
(for clarity remaining compounds were omitted and can be found
in figure S1†). The absorption spectra are all similar to 1, with
the characteristic vibronic peaks of 1 and anthracene. Only minor
(< 10 nm) red shifts (figure 4) are observed for derivatives with
thiophene substituents. These results are in well agreement with
calculations which predict only small changes in the S0 −S1 gap,
vide infra.
1−β
I(t) = I(0)
(1)
exp(t/τt)−β
The fluorescence spectra of the phenyl-substituted anthracenes
3-6 and 10 are similar to that of 1, figure 4, and have high fluo-
rescence quantum yields (table 1). However, compounds contain-
ing thiophenes show a considerable decrease in their fluorescence
quantum yield compared to 1, with quantum yields as low as 2%
for 8. The tail of the emission for these derivatives (7-9) stretches
further into the red, up to 750 nm compared to the other deriva-
tives which end closer to 600 nm, which indicates that excitation
is more delocalized as the smaller thiophene moiety can conform
to a more planar structure compared to the phenyl substituents.63
The low fluorescence quantum yield is most probably explained
by new non-radiative decay pathways that become possible as
the rotation around the anthracene-thiophene bond is easier than
the anthracene-phenyl bond which is substantially more sterically
hindered. The lack of an efficient fluorescent state makes these
derivatives less useful for applications requiring emissive materi-
als, such as OLEDs or photon-upconversion. The phenyl contain-
ing derivatives on the other hand have high fluorescence quantum
yields, many close to unity as for 1.64 Also listed in table 1 are
excited state lifetimes for the emissive compounds, these are in
general similar or slightly shorter than the lifetime of 1.
where β is a dimensionless parameter with a value between 0
and 1 indicating the fraction of initial decay that occurs through
the second-order channel,66 1 corresponding to fully second or-
der and zero to first order. I(0) is the intensity at time, t=0, and
τt is the lifetime of the triplet state.
Long triplet state life-times (> 1 ms) were observed for the
diphenyl substituted derivatives (table 1), which are beneficial
in a TTA-UC system.67 As was the case in the first excited sin-
glet state, thiophene containing derivatives also displayed shorter
triplet state life-times.
The solubility in toluene was investigated and is also presented
in table 1. All derivatives are soluble above 40 mM in toluene,
except for trifluoro-substituted 4 which is about an order of mag-
nitude less soluble. The absorption spectra of the saturated so-
lutions were recorded between two glass slides and showed no
significant change compared to the dilute spectra (S2-S11†). Also
the fluorescence of the saturated solutions were recorded. For
aryl substituted anthracenes the only changes observed could be
explained by reabsorption due to the overlap of absorption and
emission, indicating that little or no aggregation is occurring. 2
showed a new red-shifted emission which is characteristic for its
exciplex and has been reported previously.24
Nanosecond transient absorption was used in order to deter-
mine the triplet lifetime of the derivatives (table 1). The triplet
absorption was monitored at 452 nm. No triplet states were de-
6 |
1–12

Page 7 of 13
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC02626A
Table 1 Properties determined for 9,10-substituted anthracenes in toluene
a
b
Absmax
τf
(ns)
kTET
kTTA
Solubility
(mM)
τt
(ms)
a
Φf
Compound
(ε ×10−4)(Wavelength (nm))
(×109M−1s−1
)
(×109M−1s−1
)
1.21(395), 1.25(375),
1
2
3
4
5
6
7
8
9
93
115
39
0.76(356)68
1.064
6.97
-
8.61
-
2.15
3.97
1.93
1.92
1.81
2.25
2.07
2.52
2.17
1.90
2.51
0.92(401), 0.955(380),
0.56(360)
∼ 0.723
-
1.21(395), 1.28(374),
0.79(356)
0.96±0.020
1.0±0.010
0.99±0.003
0.84±0.065
0.09±0.002
0.02±0.000
0.026±0.006
6.93
6.84
5.54
5.50
-
7.73
9.55
1.73
18.95
0.043
0.005
0.043
8.50
2.31
1.22(395), 1.29(374),
8
0.795(356)
2.25
1.24(395), 1.31(375),
83
0.80(357)
1.98
1.245(396), 1.32(375),
47
0.815(357)
-
1.255(397), 1.315(377),
256
61
0.8(358)
-
1.35(400), 1.365(379),
0.815(360)
-
-
1.28(397), 1.32(376),
76
0.80(358)
-
-
1.23(396), 1.30(375),
10
a
107
0.80(357)
0.77±0.016
4.69
1.77
b
Reported values are the average of two independent measurements. PtOEP as the sensitizer.
3.3 Stern-Volmer Quenching Analysis
For efficient triplet energy transfer from a triplet sensitizer to an
acceptor requires that the triplet state of the acceptor is lower
in energy than that of the sensitizer. This is the case for the
sensitizer-acceptor pairs platinum octaethylporphyrin (PtOEP)
and 1 as well as for palladium octaethylporphyrin (PdOEP)
and 1. The energy transfer efficiency can be monitored by the
quenching of the sensitizer phosphorescence as described by the
Stern-Volmer relationship (equation 2) which relates the emission
quenching to the concentration of quencher69
:
I0
I
= 1+kTET τ0[Q]
(2)
where I0 and I are the unquenched and quenched emission in-
tensities respectively, kTET is the triplet energy transfer rate con-
stant, τ0 is the lifetime of the unquenched state and [Q] is the
concentration of quencher.
Fig. 5 Stern-Volmer plot of PtOEP (0.5 µM) phosphorescence
quenching 1 (•), 2 (x), 3 (ꢀ), 4 (N), 5 (ꢁ), 6 (O), 7 (+), 8 (J), 9 (o) and
The quenching of PdOEP and PtOEP, by the substituted an-
thracenes was studied. Stern-Volmer plots of the quenching dy-
namics of PtOEP is shown in figure 5. Similar graphs were ob-
tained for the quenching of PdOEP (figure S26†). The obtained
triplet energy transfer rate constants, kTET (table 1) are similar
for all derivatives and 1 and are all diffusion limited as expected,
they also agree with values reported for 1 in similar systems.27,70
This indicates that the first triplet state energy (T1) of the 9,10-
substituted anthracenes are all similar or lower than the triplet
state of PdOEP, 1.86 eV70 which is in agreement to that reported
for 1, 1.77 eV.71 In this context all derivatives are good candi-
dates for sensitized triplet-triplet annihilation photon upconver-
sion utilizing PdOEP or PtOEP as sensitizers and upconverted
emission was observed for all derivatives with fluorescence quan-
tum yields > 10%.
10 (ꢂ).
3.4 Theoretical Calculations
In order to reveal the changes in electronic levels due to substi-
tution patterns of the 9,10-disubstituted anthracene DFT calcula-
tions were performed. Table 2 lists the calculated energy levels
and the difference between two times the first triplet energy level
(2×T1) and the first singlet energy level (S1), which ideally is
positive but close to zero for a good annihilator in a triplet-triplet
annihilation upconversion system33
.
Rotation around the single bond between the anthracene and
ligand group was explored and a global minima at 90 degrees
were always found in good agreement to that calculated for 9-
phenylanthracene and close to 85° determined by X-ray diffrac-
1–12 | 7

Journal of Materials Chemistry C
Page 8 of 13
View Article Online
DOI: 10.1039/C5TC02626A
Table 2 Calculated excited state energy differences of anthracene
derivativesa
0.02
0.01
0
Compound S0 −S1 S1 −T1 S0 −T2 2×T1 −S1
0.02
0
1
2
3
4
5
6
7
8
9
3.10
3.03
3.10
3.10
3.10
3.10
3.08
3.05
3.07
3.10
1.72
1.67
1.73
1.73
1.73
1.73
1.71
1.69
1.71
1.73
3.23
3.24
3.23
3.23
3.23
3.23
3.22
3.20
3.22
3.23
0.34
0.31
0.36
0.36
0.36
0.36
0.34
0.33
0.35
0.36
-0.01
-0.02
-0.03
-0.04
-0.05
-0.02
-0.04
-0.06
0
2
4
× 10-6
0
1
2
3
4
5
6
7
8
9
× 10-4
× 10-3
4
2
0
10
-2
-4
0
a
All energies are reported in eV.
1
2
3
4
5
6
7
8
9
× 10-4
time (s)
tion of substituted diphenylanthracenes.72 This explains the mi-
nor effect of the substitution on the energy levels as the conju-
gation between the perpendicular aryl-substituent and the an-
thracene core is minimal compared to the coplanar orientation.
The coplanar orientation is unlikely, due to the sterical clash
between the substituents hydrogen and the 1,4,5,8-anthracene
hydrogens, resulting in a high rotational barrier for the phenyl
groups.72 The smaller thiophene substituent is expected to have
a less hindered rotation and is consistent with the observed red-
shifted emission, vide supra.
The substitution effect on the calculated energies is minimal
(table 2), as confirmed by optical absorption experiments. For ap-
plications in TTA upconversion this is a promising finding as the
spacing of the energy levels is of crucial importance for an effi-
cient system and 1, being a benchmark system, could be modified
with substituents to obtain desired properties without effecting
the energetics of the chromophore.
Fig. 6 Transient absorption measurements of 4 (1 mM) and PtOEP
(3.4µM) at 410 nm (Annihilator Decay, blue) and 650 nm (Sensitizer
decay, black) and respective fits. Inset shows the first 5 µs. Bottom
panel shows the residual of the fitted annihilator decay.
stant (kTTA), the triplet energy transfer rate constant (kTET ), the
annihilator triplet absorptivity (∆εET ), the sensitizer triplet ab-
sorptivity (∆εST ), as well as two scaling factors for the relative
magnitude of phosphorescence (aphos) and upconverted emission
(afl). The initial triplet concentration of the sensitizer was esti-
mated from the initial ground state bleach at 540 nm.
Derivatives 3 and 4 exhibit annihilation rate constants similar
but slightly lower than 1 and compounds 5 and 10 display the
lowest values of the series. The fitting also yielded triplet en-
ergy transfer rate constants kTET close to those determined in the
Stern-Volmer analysis as well as triplet absorptivities close to half
of that reported at ∼450 nm for 1, which is consistent with the
triplet-triplet absorption spectra of 1.71,73 The obtained values
can be found in ESI† together with the transient decays (figures
S21-S25†).
3.5 Upconversion Study
A long triplet lifetime and efficient triplet-triplet annihilation rate
constant are key features of an upconverting system.67 Triplet-
triplet annihilation rate constants were determined for the deriva-
tives 3 (1 mM), 4 (1 mM), 5 (0.7 mM) and 10 (1 mM) as well
as for the reference 1 (1 mM) with PtOEP (3.4 µM) as the sen-
sitizer. Samples were monitored at 410 nm as well as 650 nm
after excitation at 532 nm. Figure 6 displays the transient decays
of 4/PtOEP at 410 nm and 650 nm (inset in figure 6 shows first
5 µs) and the best fit to the data. Decays of 1, 3, 4, 5 and 10
with corresponding fits and determined fitting parameters can be
found in figure S21-S25. As seen in figure 6 there is an initial
positive feature at 410 nm, this corresponds to the absorption of
the annihilator triplet state and the sensitizer triplet, after about
100 ns delayed fluorescence of the annihilator starts to take part,
resulting in a negative feature in the transient. Whereas at 650
nm only the phosphorescence of the sensitizer is observed. Both
long (1 ms) and short (5 or 50 µs, inset figure 6) time windows
were recorded at 410 nm. The three transients (1 ms and 5/50
µs at 410 nm and 5 µs at 650 nm) were fitted globally to the
rate equations governing the system, as presented in ESI†, using
MATLAB and the built-in differential equation solver ode23s. The
fitting parameters were the triplet-triplet annihilation rate con-
The quantum yield of upconversion, the numbers of emitted
high-energy photons compared to the number of absorbed low
energy photons, is challenging to determine and to compare re-
ported values requires one to know the exact experimental condi-
tions, such as sensitizer and annihilator concentrations, light in-
tensity and oxygen concentration.34 The upconversion quantum
yield is the product of the quantum yields for each step required
to produce upconverted photons (equation 3):
ΦUC = ΦISC ×ΦTET ×ΦTTA ×Φf
(3)
Where ΦISC is the quantum yield of inter system crossing of
the triplet sensitizer, ΦTET is the triplet-energy transfer efficiency
from sensitizer to annihilator, ΦTTA is the triplet-triplet annihi-
lation quantum yield and Φf is the fluorescence quantum yield
of the annihilator. However, determining each of these quantum
yields individually for an upconverting system is not feasible. In-
stead it is common to apply the method of relative actinometry
which is frequently used for normal fluorescence quantum yield
determination (equation 4).
8 |
1–12

Page 9 of 13
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC02626A
were slightly more blue-shifted compared to thiophene and sp3-C
substituents. However the fluorescence quantum yield decreased
considerably for thiophene containing derivatives, most proba-
bly a result of a larger non-radiative decay rate. Thus for appli-
cation requiring blue emissive chromophores phenyl-substituted
9,10-anthracenes are more suitable. DFT calculations are in well
agreement with experimental measurements indicating minimal
change of the energy levels upon substitution.
Ar Fx Ir ηr2
Ax F Ix η2
ΦUC = Φr
(4)
r
x
Where Ai is the absorbance at the excitation wavelength, F
i
is the integrated emission, Ii is the excitation intensity, ni is the
refractive index and the subscripts r and x denotes the reference
and sample respectively. We employed zinc octaethylporphyrin as
the standard with a quantum yield of 6.77%.51 It is important to
point out that the maximum quantum yield for an upconversion
system is 50% as it requires two low-energy photons to produce
one high-energy photon.
Characteristic for the upconverted emission is that it shows
a quadratic dependence on the excitation intensity at low in-
tensities, which shifts to a linear dependence at higher intensi-
ties as the annihilator triplet concentration no longer limits the
annihilation process.65 Consequently the upconversion quantum
yield will increase with the excitation intensity until the linear
regime is reached. The intensity where the dependence shifts
from quadratic to linear is referred to as the threshold intensity
Ith and is an important parameter as it can be compared to the
light intensity provided from the sun at the specific wavelength.
For an efficient and practical system Ith should be equal or lower
than the intensity of the sun.
As described in equation 3, ΦUC scales with the fluorescence
quantum yield of the annihilator, an efficient system thus requires
an annihilator with a fluorescence quantum yield close to unity.
Therefore only the three derivatives with the highest quantum
yields, namely 3, 4 and 5, were chosen for the upconversion
study. As mentioned previously also compounds 6 and 10 with
intermediate fluorescence quantum yields displayed upconverted
emission.
The excitation power density dependence on the upconverted
emission is presented in figure 7. All three annihilators perform
similar to 1 where 3 and 4 perform within error the same as 1
with Ith = 18 mW/cm2, whereas 5 has a slightly higher Ith = 40
mW/cm2. In figure 7 ΦUC is seen to level out at higher excitation
intensities as expected. Consistent with the observed annihilation
rate constants, 3 and 4 exhibit yields similar to 1, but slightly
higher; 7.9% and 8.7% respectively compared to 7.7% for DPA
(1). Again 5 performs slightly worse with a ΦUC of 6.9%, this
minor decrease of ΦUC could be explained by the higher molar
absorptivity and more red-shifted absorption onset of 5 which
would result in a increased reabsorption at the high concentra-
tions used for the UC samples, but could also be a consequence
of the shorter triplet lifetime and less efficient triplet-triplet anni-
hilation process. Overall 3, 4 and 5 are efficient annihilators for
TTA-UC employing PtOEP as a sensitizer.
The three most fluorescent compounds 3, 4 and 5 were success-
fully used as annihilators for triplet-triplet annihilation upcon-
version with PtOEP as the sensitizer and quantum yields slightly
succeeding that pf DPA was observed. The main challenge for
TTA upconversion is to achieve highly efficient systems in the
solid state and some attempts to achieve this have been reported.
Mainly two methods have been employed in designing such ma-
terials, capturing annihilators and sensitizers in a polymeric or
gel matrix,29,74–79 or developing supra-molecular or polymeric
structures containing annihilators and/or sensitizers.80,81
Aiding future design of efficient blue-emitting materials based
on 9,10-substituted anthracene we demonstrate that the well
known chromophore 1 may be modified in the para-positions
with both electron withdrawing and donating substituent with-
out changing the absorption and emission properties. However
9,10-substituents introducing new non-radiative relaxation path-
ways should be avoided. The design parameters discussed here
are helpful in future synthesis of 9,10-substituted anthracenes as
modifying 1 in this way can be practical and in some cases neces-
sary for materials design. For example, one can envision improv-
ing the affinity of 1 for the matrix or the sensitizer by introducing
suitable side groups without effecting the useful properties inher-
ent to the 1 chromophore and recently two examples of this was
reported by Kimizuka and co-workers.20,50
5 Acknowledgement
The authors acknowledge funding from the Swedish Energy
Agency (36436-1), Chalmers Materials Area of Advance, the
Swedish Research Council (B0361301), Swedish strategic re-
search council (SSF) and Knut and Alice Walllenberg foundation.
Also Computer time at Chalmers Centre for Computational Sci-
ence and Engineering (C3SE) provided by the Swedish National
Infrastructure for Computing (SNIC) is acknowledged.
References
1 M. O. Forster, Nature, 1921, 108, 108–109.
2 H.-G. Franck and J. Stadelhofer, Industrial Aromatic Chem-
istry, Springer-Verlag, Berlin Heidelberg, 1st edn., 1988.
3 M. H. Ho, B. Balaganesan and C. H. Chen, Isr. J. Chem., 2012,
52, 484–495.
4 Conclusion
4 J. Huang, J.-H. Su and H. Tian, J. Mater. Chem., 2012, 22,
10977.
Eight 9,10-substituted anthracenes containing either electron do-
nating, electron withdrawing or both types of groups have been
synthesized and their photophysical properties have been stud-
ied and compared to the two previous known 9,10-substituted
anthracenes DPA and DMA (1 and 2 respectively). The type of
substitution at the 9,10-position was shown to have only a minor
influence on the absorption spectrum, where phenyl-substituents
5 T. Sereviˇcius, R. Komskis, P. Adom˙enas, O. Adom˙enien˙e,
V. Jankauskas, A. Gruodis, K. Kazlauskas and S. Jurš˙enas,
Phys. Chem. Chem. Phys., 2014, 16, 7089–101.
6 H. Ihmels, A. Meiswinkel and C. J. Mohrschladt, Org. Lett.,
2000, 2, 2865–2867.
1–12 | 9

Journal of Materials Chemistry C
Page 10 of 13
View Article Online
DOI: 10.1039/C5TC02626A
7 B. Valeur, Coord. Chem. Rev., 2000, 205, 3–40.
8, 103–125.
8 H. Lu, B. Xu, Y. Dong, F. Chen, Y. Li, Z. Li, J. He, H. Li and
W. Tian, Langmuir, 2010, 26, 6838–6844.
33 T. W. Schmidt and F. N. Castellano, J. Phys. Chem. Lett., 2014,
5, 4062–4072.
9 W. Leo, Techniques for nuclear and particle physics experiments:
a how-to approach, Springer-Verlag, Berlin Heidelberg, 2nd
edn., 1994.
34 V. Gray, D. Dzebo, M. Abrahamsson, B. Albinsson and
K. Moth-Poulsen, Phys. Chem. Chem. Phys., 2014, 16, 10345–
52.
10 S. Baluschev, T. Miteva, V. Yakutkin, G. Nelles, A. Yasuda and
G. Wegner, Phys. Rev. Lett., 2006, 97, 7–9.
35 T. Trupke, M. A. Green and P. Würfel, J. Appl. Phys., 2002,
92, 4117–4122.
11 T. N. Singh-Rachford, R. R. Islangulov and F. N. Castellano, J.
Phys. Chem. A, 2008, 112, 3906–3910.
36 N. J. Ekins-Daukes and T. W. Schmidt, Appl. Phys. Lett., 2008,
93, 063507.
12 H.-C. Chen, C.-Y. Hung, K.-H. Wang, H.-L. Chen, W. S. Fann,
F.-C. Chien, P. Chen, T. J. Chow, C.-P. Hsu and S.-S. Sun,
Chem. Commun., 2009, 4064–4066.
37 J. de Wild, a. Meijerink, J. K. Rath, W. G. J. H. M. van Sark
and R. E. I. Schropp, Energy Environ. Sci., 2011, 4, 4835.
38 Y. Y. Cheng, B. Fückel, R. W. MacQueen, T. Khoury, R. G.
C. R. Clady, T. F. Schulze, N. J. Ekins-Daukes, M. J. Crossley,
B. Stannowski, K. Lips and T. W. Schmidt, Energy Environ.
Sci., 2012, 5, 6953.
13 S. Ji, W. Wu, W. Wu, H. Guo and J. Zhao, Angew. Chemie - Int.
Ed., 2011, 50, 1626–1629.
14 H. Sun, H. Guo, W. Wu, X. Liu and J. Zhao, Dalton Trans.,
2011, 40, 7834–7841.
39 T. F. Schulze, J. Czolk, Y.-Y. Cheng, B. Fückel, R. W. Mac-
Queen, T. Khoury, M. J. Crossley, B. Stannowski, K. Lips,
U. Lemmer, A. Colsmann and T. W. Schmidt, J. Phys. Chem. C,
2012, 116, 22794–22801.
15 R. S. Khnayzer, J. Blumhoff, J. A. Harrington, A. Haefele,
F. Deng and F. N. Castellano, Chem. Commun., 2012, 48, 209.
16 F. Deng, J. Blumhoff and F. N. Castellano, J. Phys. Chem. A,
2013, 117, 4412–4419.
40 T. F. Schulze, Y. Y. Cheng, B. Fckel, R. W. MacQueen,
A. Danos, N. J. L. K. Davis, M. J. Y. Tayebjee, T. Khoury, R. G.
C. R. Clady, N. J. Ekins-Daukes, M. J. Crossley, B. Stannowski,
K. Lips and T. W. Schmidt, Aust. J. Chem., 2012, 65, 480–485.
41 J. A. Briggs, A. C. Atre and J. A. Dionne, J. Appl. Phys., 2013,
113, 124509.
17 P. Duan, N. Yanai and N. Kimizuka, J. Am. Chem. Soc., 2013,
135, 19056–19059.
18 X. Cao, B. Hu and P. Zhang, J. Phys. Chem. Lett., 2013, 2334–
2338.
19 S. H. C. Askes, A. Bahreman and S. Bonnet, Angew. Chemie -
Int. Ed., 2014, 53, 1029–1033.
42 A. Nattestad, Y. Cheng, R. Macqueen, T. Schulze, F. Thomp-
son, A. Mozer, B. Fu, T. Khoury, M. Crossley, K. Lips, G. Wal-
lace and T. W. Schmidt, J. Phys. Chem. Lett., 2013, 4, 2073–
2078.
20 T. Ogawa, N. Yanai, A. Monguzzi and N. Kimizuka, Sci. Rep.,
2015, 5, 10882.
21 Z. Huang, X. Li, M. Mahboub, K. M. Hanson, V. M. Nichols,
H. Le, M. L. Tang and C. J. Bardeen, Nano Letters, 2015, 15,
5552–5557.
43 J.-H. Kim and J.-H. Kim, J. Am. Chem. Soc., 2012, 134,
17478–17481.
44 K. Börjesson, D. Dzebo, B. Albinsson and K. Moth-Poulsen, J.
Mater. Chem. A, 2013, 1, 8521–8524.
22 A. R. Horrocks and F. Wilkinson, Proc. R. Soc. A Math. Phys.
Eng. Sci., 1968, 306, 257–273.
45 C. A. Parker and C. G. Hatchard, Proc. R. Soc. A Math. Phys.
Eng. Sci., 1962, 269, 574–584.
23 R. L. Barnes and J. B. Birks, Proc. R. Soc. A Math. Phys. Eng.
Sci., 1966, 291, 570–582.
46 C. A. Parker and C. G. Hatchard, Proc. Chem. Soc., 1962, 1962,
386–387.
24 C. A. Parker and T. A. Joyce, Chem. Commun., 1967, 744–745.
25 C. E. McCusker and F. N. Castellano, Inorg. Chem., 2015, 54,
6035–6042.
47 C. A. Parker, Proc. R. Soc. A Math. Phys. Eng. Sci., 1963, 276,
125–135.
26 R. R. Islangulov and F. N. Castellano, Angew. Chemie - Int. Ed.,
2006, 45, 5957–5959.
48 Y. Y. Cheng, B. Fückel, T. Khoury, R. G. C. R. Clady, M. J. Y.
Tayebjee, N. J. Ekins-Daukes, M. J. Crossley and T. W.
Schmidt, J. Phys. Chem. Lett., 2010, 1, 1795–1799.
49 R. Vadrucci, C. Weder and Y. C. Simon, J. Mater. Chem. C,
2014, 2, 2837–2841.
27 R. R. Islangulov, D. V. Kozlov and F. N. Castellano, Chem. Com-
mun., 2005, 1, 3776–3778.
28 S. Baluschev, V. Yakutkin, G. Wegner, T. Miteva, G. Nelles,
A. Yasuda, S. Chernov, S. Aleshchenkov and a. Cheprakov,
Appl. Phys. Lett., 2007, 90, 1–4.
50 P. Mahato, A. Monguzzi, N. Yanai, T. Yamada and
N. Kimizuka, Nat. Mater., 2015, 14, 924–930.
51 X. Liu, E. K. L. Yeow, S. Velate and R. P. Steer, Phys. Chem.
Chem. Phys., 2006, 8, 1298–1309.
29 R. R. Islangulov, J. Lott, C. Weder and F. N. Castellano, J. Am.
Chem. Soc., 2007, 129, 12652–12653.
30 S. Baluschev, V. Yakutkin, T. Miteva, G. Wegner, T. Roberts,
G. Nelles, A. Yasuda, S. Chernov, S. Aleshchenkov and
A. Cheprakov, New J. Phys., 2008, 10, 013007.
31 T. N. Singh-Rachford and F. N. Castellano, J. Phys. Chem. A,
2009, 113, 5912–5917.
52 K. Börjesson, M. Gilbert, D. Dzebo, B. Albinsson and K. Moth-
Poulsen, RSC Adv., 2014, 4, 19846.
53 S. Kotha, A. K. Ghosh and K. D. Deodhar, Synthesis, 2004,
549–557.
54 J. Y. Hu, Y. J. Pu, F. Satoh, S. Kawata, H. Katagiri, H. Sasabe
32 T. F. Schulze and T. W. Schmidt, Energy Environ. Sci., 2015,
10 |
1–12

Page 11 of 13
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC02626A
and J. Kido, Adv. Funct. Mater., 2014, 24, 2064–2071.
J. Phys. Chem. Lett., 2012, 3, 299–303.
55 A. Becke, J. Chem. Phys., 1993, 98, 5648–5652.
56 C. Lee, W. Yang and R. Parr, Phys. Rev. B, 1988, 37, 785–789.
57 R. Ditchfield, W. J. Hehre and J. A. Pople, J. Chem. Phys.,
1971, 54, 724–728.
66 S. Bachilo and R. Weisman, J. Phys. Chem. A, 2000, 104,
7711–7714.
67 A. Danos, R. W. MacQueen, Y. Y. Cheng, M. Dvorak, T. a.
Darwish, D. R. McCamey and T. W. Schmidt, J. Phys. Chem.
Lett., 2015, 10.1021/acs.jpclett.5b01271.
58 W. J. Hehre, R. Ditchfield and J. A. Pople, J. Chem. Phys.,
1972, 56, 2257–2261.
68 E. Gazis, UV Atlas of organic compounds, Vol. III, Butterworths,
London, 1967.
59 M. M. Francl, W. J. Pietro, W. J. Hehre, J. S. Binkley, M. S.
Gordon, D. J. DeFrees and J. A. Pople, J. Chem. Phys., 1982,
77, 3654–3665.
69 J. R. Lakowicz, Principles of Fluorescence Spectroscopy,
Springer Science, New York, 3rd edn., 2006.
70 M. Penconi, F. Ortica, F. Elisei and P. L. Gentili, J. Lumin.,
2013, 135, 265–270.
60 M. J. Frisch, G. W. Rucks, H. B. Schlegel, G. E. Scuse-
ria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. Montgomery, J. A., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin,
V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
J. C. Rendell, A.; Burant, S. S. Iyengar, J. Tomasi, M. Cossi,
N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Strat-
mann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J.
Fox, Gaussian 09, 2009.
71 S. Chattopadhyay, C. V. Kumar and P. Das, Chem. Phys. Lett.,
1983, 98, 250–254.
72 K. Nikitin, H. Müller-Bunz, Y. Ortin, J. Muldoon and M. J.
McGlinchey, Org. Lett., 2011, 13, 256–259.
73 T. J. Kemp and J. P. Roberts, Trans. Faraday Soc., 1969, 65,
725–731.
74 T. N. Singh-Rachford, J. Lott, C. Weder and F. N. Castellano,
J. Am. Chem. Soc., 2009, 131, 12007–12014.
75 Y. C. Simon and C. Weder, J. Mater. Chem., 2012, 22, 20817.
76 J. H. Kim, F. Deng, F. N. Castellano and J. H. Kim, Chem.
Mater., 2012, 24, 2250–2252.
77 P. Duan, N. Yanai, H. Nagatomi and N. Kimizuka, J. Am. Chem.
Soc., 2015, 137, 1887–1894.
78 K. Sripathy, R. W. MacQueen, J. R. Peterson, Y. Y. Cheng,
M. Dvorák, D. R. McCamey, N. D. Treat, N. Stingelin and T. W.
Schmidt, J. Mater. Chem. C, 2015, 3, 616–622.
79 R. Vadrucci, C. Weder and Y. C. Simon, Mater. Horiz., 2015,
2, 120–124.
61 R. Bauernschmitt and R. Ahlrichs, Chem. Phys. Lett., 1996,
256, 454–464.
62 E. Casida, C. Jamorski, K. C. Casida and D. R. Salahub, J.
Chem. Phys., 1998, 108, 4439–4449.
80 A. J. Tilley, M. J. Kim, M. Chen and K. P. Ghiggino, Polym.,
2013, 54, 2865–2872.
63 J.-H. Ho, Y.-H. Chen, L.-T. Chou, P.-W. Lai and P.-S. Chen,
Tetrahedron Lett., 2014, 55, 5727–5731.
81 A. J. Tilley, B. E. Robotham, R. P. Steer and K. P. Ghiggino,
Chem. Phys. Lett., 2015, 618, 198–202.
64 G. Heinrich, S. Schoof and H. Gusten, J. Photochem., 1974, 3,
315–320.
65 A. Haefele, J. Blumhoff, R. S. Khnayzer and F. N. Castellano,
1–12 | 11

Journal of Materials Chemistry C
Page 12 of 13
View Article Online
DOI: 10.1039/C5TC02626A
Fig. 7 Left: Double logarithmic plot of integrated upconverted emission dependence on excitation power density (532 nm) of solutions containing
PtOEP, 15 µM and 0.5 mM annihilator. Right: Upconverted emission quantum yield (ΦUC) as a function of excitation power density of the same
solutions. 1 (•), 3 (ꢀ), 4 (N) and 5 (ꢁ).
12 |
1–12

Page 13 of 13
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC02626A