Blue: Versus yellow emission in bipolar fluorenone derivatives: The impact of aggregation and hydrogen bonding

Article abstract of DOI:10.1039/c7tc05798a

Three donor-π-acceptor-π-donor multichromophore fluorenone-centered compounds are presented. The π-bridges between the fluorenone and carbazole donors contain ethynyl moieties linked to various branched spacing moieties, such as triphenylamine, 1,3,5-triphenylbenzene and 9-phenylcarbazole. Differences in the photophysical, photoelectrical, thermal and charge-transporting characteristics of the three compounds are analyzed by means of experimental and density functional theory (DFT) methods. The investigated compounds exhibit good ambipolar charge transport behavior with mobility values exceeding 10^-3 cm² V^-1 s^-1. The compounds exhibit interesting photoluminescence properties, which are strongly influenced by the important tendency of these compounds in solution to form strongly bound ground state aggregates. Photoluminescence emission of these materials is found to originate predominantly from intramolecular transitions of π-π_CT? nature which experience a strong redshift and an intensity decrease from the aggregation and intermolecular H-bonds. A slowly evolving equilibrium between strongly aggregated molecules and free ones is observed in THF solutions, resulting in the emission color swapping gradually from yellow to blue with a drastic intensity increase. The correlation of the aggregation strength with the absorption and emission properties, photoluminescence quantum yield, and the time needed for color swapping is discussed. Furthermore, seldom observed photoluminescence intensity enhancement with temperature increase was detected in non-polar media.

Full text of DOI:10.1039/c7tc05798a

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ISSN 2050-7526
PAPER
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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Blue versus Yellow Emission in Bipolar Fluorenone Derivatives:
Impact of Aggregation and Hydrogen Bonding
Received 00th January 20xx,
Accepted 00th January 20xx
c
N. A. Kukhtaa, b, D. Volyniukb J. V. Grazulevicius b*, G. Sini *
,
Three donor-π--acceptor-π-donor multichromophore fluorenone-centered compounds are presented. The π-bridges
between fluorenone and carbazole donors contain ethynyl moieties linked to various branched spacing moieties, such as
triphenylamine, 1,3,5-triphenylbenzene and 9-phenylcarbazole. Differences in photophysical, photoelectrical, thermal and
charge-transporting characteristics of the three compounds are analyzed by means of experimental and density functional
theory (DFT) methods. The investigated compounds exhibit good ambipolar charge transport behavior with mobility values
exceeding 10-3 cm2 V-1 s-1. The compounds exhibit interesting photoluminescence properties, which are strongly influenced
by the important tendency of these compounds in solution to form strongly bounded ground state aggregates.
Photoluminescence emission of these materials is found to originate dominantly from intramolecular transitions of π–π*CT
nature which experience strong redshift and intensity decrease from the aggregation and intermolecular H-bonds. A
slowly evolving equilibrium between strongly aggregated molecules and free ones is observed in THF solutions, resulting in
emission color swapping gradually from yellow to blue with drastic intensity increase. Correlation of the aggregation
strength with the absorption and emission properties, photoluminescence quantum yield, and the time needed for color
swapping is discussed. Furthermore, seldom observed photoluminescence intensity enhancement with the temperature
DOI: 10.1039/x0xx00000x
www.rsc.org/
increase
was
detected
in
non-polar
media.
wide energy gap materials 6.
1. Introduction
Despite their great diversity in the nature of the donor and
spacer moieties, these compounds present strong similarities
in their optical spectra, generally exhibiting a week, broad, and
shapeless absorption band in the region 400-500 nm, and
strong and efficient emission in the yellow-red region. These
similarities were recently shown to be due to the strong
tendency of these compounds toward aggregation in their
ground state and to the inherent impact of the hydrogen
bonds established by means of C=O groups 7. Both effects
redshift and weaken the intrinsic absorption and emission of
the fluorenone-based compounds. In THF the aggregates and
the H-bonds were found to disappear after long time, which
was translated by a spectacular change in color from yellow to
blue and the increase of the emission intensity by several
orders of magnitude. These findings are consequently
expected to be of great interest in the domain of OLEDs. Given
that the intrinsic emission color of 2,7-linked fluorenones is
not the yellow-red but the blue one 7, new design strategies
could be developed in order to obtain fluorenone-based blue
emitters. The guiding strategy for obtaining pure and stable
blue emission should consequently consist in protecting
fluorenones from aggregation and their keto groups from
establishing H-bonds. These findings are important for the
fluorene-based OLEDs equally, as fluorenones have been
suspected to be at the origin of the color degradation of
fluorene-based blue emitters 8–10. New solutions to avoid color
degradation of fluorene-based compounds could consequently
In the field of organic optoelectronics, the usage of
multichromophore molecular architecture leads to great
diversity in the optical, photophysical, charge-transporting
characteristics of compounds. Exploitation of the strongly
electron-accepting rigid fluorenone moiety results in efficient
1
electron mobility . Judicious combination of fluorenone cores
with donor groups in donor-bridge-acceptor architectures not
only allows to combine advantages of both donor and acceptor
in one molecule, but additionally induces new interesting
properties. Donating carbazole fragment provides for instance
2
high thermal stability and remarkable hole mobility
.
Triphenylamine unit not only provides excellent charge-
3
transporting behavior , but due to its propeller shape proves
to be a good building block for aggregation-induced-emission
(AIE) luminogenes 4,5. Finally, because of its twisted skeleton,
1,3,5-triphenylbenzene finds application in the preparation of
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follow similar ideas as those designed for fluorenone-based transformation is found to be the demolition of the aggregates
ones, by protecting from establishing H-bonds the sites having in THF solution.
potential toward oxidation.
7
However, several questions raised by the previous study still
2. Results and discussion
need to be addressed. It is for instance not clear how these
compounds transform from aggregated- but strongly (yellow)
2.1 Synthesis
emissive state in non-polar solvents, to quasi-totally quenched
(yellow) emission in fresh THF solutions, which solution
Chart
1
depicts the chemical structures of the
FN-TPB and FN-PCz
transforms with time (old THF solution) in strongly blue
emissive one. The time needed for the THF solutions to swap
from quenched yellow to intense blue emission is expected to
be closely correlated to the aggregation strength. Additionally,
the nature of emissive or non-emissive species in different
phases needs deeper investigation. It was suggested that the
emission of all species during yellow-to-blue transformation of
FN-PCz (Chart 1) is of intramolecular nature, involving states
located in close proximity of the fluorenone core. However,
stronger aggregation could result in intermolecular charge
transfer transitions, with drastic impact in emission color and
intensity.
multichromophore compounds FN-TPA
,
.
All the molecules under consideration possess C2 symmetry
reached by the usage of symmetrical 2,7-functionalized
fluorenone moiety. The molecules comprise donating
carbazolyl groups, linked to the accepting core by the various
branched spacer fragments, responsible for the butterfly-
shape, i.e. triphenylamine (TPA), 1,3,5-triphenylbenzene (TPB)
and 9-phenylcarbazole (PCz). The ethynyl π-bridge was
employed to achieve more efficient conjugation between the
core and the side arms.
Scheme
1 presents the synthetic routes, involving the
divergent strategy, towards the multichromophore fluorenone
derivatives. On the first step, star-shaped spacer units were
In order to obtain more insight on the impact of these effects
on the emission properties of fluorenone-based compounds,
we present here two new compounds, differing from FN-PCz
only by the nature of the spacer (Chart 1). The two new
compounds along with FN-PCz were extensively characterized
by means of a joint theoretical and experimental approach.
The new molecules combine the advantages of fluorenone,
carbazole, triphenylamine and triphenylbenzene, exhibiting
not only high thermal stability, balanced ambipolar charge
transport and AIE features, but also demonstrated the
intriguing emission blue-shift- and intensity enhancement
upon the disaggregation and H-bond breaking. The present
results allow deducing that the emission in these compounds
remains of intramolecular nature and is located around the
fluorenone moiety independently of the aggregation strength,
whereas the time-consuming step during the yellow-to-blues
obtained. Halogenated triphenylamine and 9-phenylcarbazole
11
derivatives 1 and 3 were prepared by Ulmann condensation
12
followed by the iodination reaction in Tucker’s conditions
.
1,3,5-Tris(4-iodophenyl)benzene (2) was synthesized by the
electrophilic cyclization reaction catalized by SiCl4 13. Further
N–C coupling of the halogenated derivatives with 3,6-di-tert-
11
butylcarbazole (4) in Ulmann conditions
branched precursors 1a 2a 3a
trimethylsilylethynyl group 14, producing the intermediates 1b
2b
3b, followed by the deprotection reaction 15, resulted in
the functionalized branched precursors 1c 2c 3c. Hagihara-
Sonogashira reaction of the latter terminal alkynes with 2,7-
diiodofluorenone gave rise to the target compounds FN-TPA
FN-TPB and FN-PCz
yielded the
,
,
. Introduction of the
,
,
,
,
14
5
,
.
Chart 1. Chemical structures of the multichromophore fluorenone derivatives.
2 | J. Name., 2012, 00, 1-3
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Scheme 1. Synthetic routes towards the multichromophore fluorenone derivatives.
The newly synthesized butterfly-shaped fluorenone adducts triphenylbenzene spacer. Remarkable thermal stability was
were characterized by MALDITOF mass spectrometry, previously reported for the TPB derivatives 16,17, however, in
1
elemental analysis, ATR-FTIR, H and 13C NMR spectroscopies. our case the improvement of FN-TPB thermal stability can be
Thus, 13C NMR spectra of all the target compounds contain a additionally explained by the smaller amount of prominent-to-
characteristic signal at 192 ppm corresponding to the carbon degradation C–N bonds (the enthalpy of C-C bond is higher
atom of C=O group, as well as the signals at 78-92 ppm than that of C-N 18), comparing to FN-TPA and FN-PCz
.
attributed to C≡C fragment peaks. The evidence of the keto The effect of the variation of the spacer was further
and ethynyl groups can be proved by the presence of the investigated by DSC (Table 1). Owing to the involvement of the
appropriate bands in the IR spectra at 1741-1748 and 2211- branched side arms with the alkylated outer carbazolyl groups,
2240 cm-1, respectively. Characteristic singlet at ca. 1.40 ppm the target fluorenones were obtained as amorphous powders.
of the CH3- group can be observed in proton NMR spectra of Therefore, as expected, only glass transitions were revealed by
the synthesized derivatives.
DSC. The glass transition temperatures were found to be
o
o
extremely high, ranging from 238 C to 293 C. The variety of
Tg values of fluorenone adducts can be assigned to different
rigidity of the spacer units. Thus, propeller-shaped labile TPA
2.2 Thermal characteristics
Thermal stability of the compounds was evaluated by TGA and TPB moieties with twisted phenyl groups (Figure 1) reduce
(Table 1). Due to the increased molar mass (ca. 1900 g/mol), glass transition temperature of FN-TPA and FN-TPB (238 and
rigid structure and employing of thermally stable 265 oC, respectively). In turn, condensed rigid 9-
19
chromophores, all the target materials exhibited outstanding phenylcarbazole unit
is responsible for the significant
o
thermal stability. Thus, TGA experiments revealed 5% weight increase of Tg (293 C for FN-PCz) by inhibiting rotational and
loss temperatures (TID) ranging from 481 to 500 oC. The highest vibrational
molecular
motions.
stability was displayed by FN-TPB
,
bearing 1,3,5-
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Table 1. Thermal, electrochemical and photoelectrical characteristics of FN-TPA
E1/2 c [V]
,
FN-TPB and FN-PCz
EACVe [eV]
Compound
FN-TPA
Tga [oC]
TIDb [oC]
E1/2 c [V]
IPCVd [eV]
Eg(CV)f [eV]
IPEPg [eV]
5.45
ox
red
238
494
0.58
0.83
0.52
-1.40
-1.36
-1.53
5.38
3.39
3.43
3.26
1.98
FN-TPB
265
500
5.63
2.19
5.53
FN-PCz
293
481
5.32
2.06
5.46
aDetermined by DSC (at a heating rate of 10 oC/min under nitrogen atmosphere) from the second heating scan. b Determined by
c
TGA (at a heating rate of 20 oC/min under nitrogen atmosphere). Determined by cyclovoltammetry for the dilute CH2Cl2
d
e
solutions. Estimated from the halfwave oxidation potential using the relationship IPCV = |e|(4.8 + Eox1/2). Estimated from the
halfwave reduction potential using the relationship EACV = |e|(4.8 – Ered1/2). f Determined from the onset of λabsmax . g Determined
from electron photoemission spectra of the thin films
A selected set of molecular orbitals of the three compounds is
2.3 Structural and electronic properties
shown in Fig. 1, whereas the energy diagram involving several
occupied and virtual orbitals is given in Figure 1 (c). Similarly to
The ground-state gas-phase optimized geometries of the previous calculations,25 the LUMOs of the three compounds
target multichromophore compounds are shown in Figure 1. In are localized on the electron-deficient fluorenone fragment,
further calculations, the real tert-butyl substituents are involving additionally the ethynyl π-bridge, whereas the
replaced by methyl groups, which has no impact on the LUMO+1 is delocalized over the whole FN-di(CCPh) bridge. As
discussions in this work. The coplanar conformation of the expected, the HOMOs are localized at the donor part of each
central part is sufficiently maintained by the usage of the 2,7- molecule, however displaying some differences depending on
7
ethynyl substituted fluorenone core. Small dihedral angles the geometry and donor strength of the spacer. While other
(0.5−2o) between the central core and the branched arms MOs, lower in energy, will be shown to dominate the optical
indicate efficient conjugation between the chromophores. In properties of these compounds (next section), the comparison
the case of FN-TPA, the steric hindrance caused by the phenyl between the corresponding HOMOs illustrates an important
rings around the central nitrogen atom of the TPA moieties difference across the series: the π-conjugation between the
generates the propeller shape of the molecule 20. The dihedral peripheral di-Cz and the di-CCPh moieties increases in the
angle between the phenyl units and nitrogen atom is 37o, in order TPB<Cz<TPA. Indeed, in the case of FN-TPA, HOMO
agreement with previously reported calculations on the TPA exhibits important contributions from the TPA and the ethynyl
derivatives 21,22. The molecule of FN-TPB as well possesses moieties, whereas the HOMO of FN-TPB is mainly localized at
propeller shape, 16,23, with the twisted by 38o outer phenyl the peripheral carbazole units, slightly involving the phenyl
groups. PCz moiety, introduced to the branched part of FN- rings of TPB. An intermediate situation is found in the case of
PCz, divides the molecular skeleton into two parts twisted by FN-PCz exhibiting partial HOMO delocalization through the
an angle of 53o, which is slightly smaller than the torsion angle inner carbazole spacer. These differences are consequently
reported for the “naked” 9-phenylcarbazole (ca 60o) 24. In the reflected in the HOMO energy trend, the later ones increasing
molecules of all the target compounds the peripheral in the order FN-TPB<FN-PCz<FN-TPA (Figure 1).
carbazole moieties are twisted by 51-56o.
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2.4 Electrochemical and photoelectrical properties
Electrochemical behaviour of the multichromophore derivatives
was probed by cyclic voltammetry (CV) for the characterization of
the produced charged species and elucidation of electronic levels
(Figure 2, Table 1). Evidently, all the synthesized fluorenone adducts
exhibit reversible oxidation and reduction in the CV traces, proving
the electrochemical stability of the compounds. The similar values
of the half-wave reduction potential (Ered1/2) suggest the formation
of fluorenone radical anion 26, in agreement with the exclusively
fluorenone-localized LUMOs (see Figure 1). In turn, the effect of the
branched spacer on electrochemical behaviour is revealed in the
positive scale (oxidation) of CV measurements. Thus, FN-TPA
exhibits three oxidation peaks, FN-PCz shows two, while FN-TPB
shows only one. Apparently, the shape of HOMO orbitals (Figure 1
(b)) and the energy diagram shown in Figure 1 (c) can be involved
for the explanation of the oxidation signal positions. Since the
HOMO energy of FN-TPB is the lowest across the series and HOMO
Figure 1. (a) Geometries and (b) frontier orbitals of FN-TPA
,
FN-TPB and FN-PCz obtained at the BMK/6-31G level of theory
(gas phase). The encircled parts indicate the spacer fragments.
(c) Energy diagram involving several occupied and virtual
orbitals.
1/2
is mainly located at the outer alkylated carbazole, E ox at 0.83 V
can be attributed to the electron withdrawal from above
mentioned
fragment.
The
similar
position
of
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roughly follow the evolution of HOMO energy across the series, the
mismatch between the IPCV and HOMO trends between FN-TPA and
FN-PCz, being probably due to the differences in intermolecular
interactions in the experimental environment.
The high values of electron affinity, falling in the range 3.36-3.43
eV, indicate strong electron accepting ability of fluorenone
additionally enhanced by the presence of diphenyl-ethynyl
substituents as compared to fluorenone (3.07 eV) 29. Calculated
electrochemical gaps (Eg(CV)) show similar trends as IPCV
.
Electron photoemission (in air) was employed for the determination
30
of solid layer ionization potentials (IPEP
)
(Table 1). Three
fluorenone derivatives exhibited close IPEP values falling in the
range 5.45-5.53 eV.
Figure 2. Cyclic voltammetry curves recorded for 10-3M CH2Cl2
solutions and electric field dependencies FN-TPA, FN-TPB and FN-
PCz.
2.5 Absorption spectra
The absorption of fluorenone derivatives, recorded for the dilute
liquid (hexane), solid (Zeonex polymer) solutions, and for the neat
films are shown at Figures 3 (a). Photophysical characteristics of FN-
TPA, FN-TPB and FN-PCz are presented in Table 2. The theoretical
absorption spectra are shown in Figure 3 (b,c). Absorption spectra
of FN-TPA, FN-TPB and FN-PCz extend to lower energies beyond the
the second oxidation potentials of FN-TPA and FN-PCz supports this
assignment. The occurrence of an additional oxidation peak at
lower potential (0.52 V) in CV curves of FN-PCz seems to be due to
the HOMO delocalization over the peripheral- and the inner
carbazole 27. As for FN-TPA, the peak at 0.58 V can be ascribed to
oxidation of TPA unit 28. Interestingly, FN-TPA shows a third
oxidation peak. As far as FN-TPA exhibits the highest EHOMO and the
HOMO is expanded to the phenylethynyl group, we suggest E 1/2ox at
1.38 V stemming from the electron withdrawal from the latter
fragment, consistently with the previously reported results 28. The
33
34
absorption bands of single carbazole
,
fluorenone
,
35
17
triphenylamine and 1,3,5-triphenylbenzene moieties involved,
indicating the enhanced conjugation within the molecules. The
profiles and peak positions of the experimental UV/Vis spectra
recorded for the solutions in different media exhibit a very weak
and broad low energy band (LEB). The next higher energy band
located at around 350 nm will be reported hereafter as HEB. The
LEB of FN-TPB and FN-PCz are of almost identical shape (very
broad) and intensity, and very similar positions (maxima at 452 nm
and 447 nm respectively), whereas some redshift and a slightly
larger intensity of this band is observed for FN-TPA. The above
similar trends are reproduced by the theoretical absorption spectra
shown in Figure 3 (b), all result in concert suggesting same nature
solid state ionization potentials (IPCV) and electron affinities (EACV
)
1/2
were evaluated using the approximations, IPCV = |e|(4.8 + Eox
)
and EACV = |e|(4.8 – Ered1/2), respectively 27. Since FN-TPA and FN-
24
PCz exploit strongly donating spacer parts (TPA and PCz
,
respectively), the values of IPCV are quite similar (5.38 and 5.32 eV).
On the contrary, FN-TPB possesses higher ionization potential (5.63
eV). In good agreement with the Koopmans’ theorem, the IP values
for
the
LEB
of
the
three
compounds.
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Figure 3. (a) UV/Vis absorption and photoluminescence (λex = 350
nm) spectra of FN-TPA, FN-TPB and FN-PCz recorded for 10-5
M
hexane and THF solutions, for solid solutions in Zeonex polymer (1
wt.% of compound), and for the neat films. (b) Theoretical
absorption spectra of the isolated FN-PCz, FN-TPA, and FN-TPB
obtained by TDDFT calculations at the BMK/6-31G level in gas
phase. (c) Theoretical absorption spectra of FN-PCz isolated and in
the presence of two methanol molecules. (reprinted with
7
permission from reference ); (d) normalized absorption spectra of
old (1 month, blue line), 5 months (blue dash line), and fresh (cyan
line) THF 10-5M solutions of FN-TPA, FN-TPB and FN-PCz; UV/Vis
absorption spectra of (e) FN-TPA, (f) FN-TPB and (g) FN-PCz
recorded for 10-5 M hexane, dodecane, ethanol, tetrahydrofuran, o-
dichlorobenzene, tetrachloromethane and tetrahydrofuran/water
solutions and for the neat films. Reproduced with permission from
the editors. Copyright © 2016, American Chemical Society.
2.5.1 Nature of the absorption bands. The energy diagram of four
selected excited states for FN-TPA, FN-TPB, and FN-PCz obtained by
TDDFT calculations is shown in Figure 4 (a), whereas the natural
transition orbitals (NTO) corresponding to the selected states are
shown in Figure 4 (b). As expected, both figures show global
similarity between the three compounds, but also some
quantitative differences. We firstly focus on their similarities.
In the case of FN-PCz, the nature of the LEB has been discussed in
7
details elsewhere. The main conclusions from our previous study
on FN-PCz are reported here: (i) the LEB is of π-π*CT nature. (ii) FN-
PCz exhibits ground state (GS) aggregation in solvents of different
nature and polarity. Compared to isolated compounds, this GS
aggregation translates in LEB and HEB redshift by 50-90 nm
depending on the solvent nature (Figure 3 (e-g)), and in decrease of
the
intrinsic
LEB
intensity.
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absorption LEB for the solutions in hexane, dodecane, CCl4, THF,
and o-DCB are almost identical, whereas strong redshift by 35-100
nm (onsets) is observed for neat films and for the solutions in protic
solvents (THF/water and ethanol) as compared to the
corresponding spectra of the solutions in hexane. Note that
important quantitative differences can also be observed between
the three compounds: (i) the absorption spectrum of FN-TPB in
ethanol shows drastic LEB redshift (from 493 nm to 600 nm) and
intensity enhancement, which is much more important than in the
case of FN-TPA and FN-PCz (Figure 3 (e, g)). In the case of FN-PCz,
this effect in ethanol has been explained by the establishment of
7
C=O…..HO-Et hydrogen bonds (H-bonds) at the keto group. (ii) the
effect of water and solid state (neat film) is larger in the case of FN-
TPA. These differences suggest that while intermolecular
interactions of similar nature as for FN-PCz could be safely
extended to FN-TPA and FN-TPB, the extent of their impact on the
photophysical properties of these compounds strongly depends on
the nature of the spacers.
Despite the above quantitative differences across the series, the
main information to retain here is the important similarity between
the three compounds wrt both their intramolecular properties and
their intermolecular interactions. This allows us to extend to FN-TPA
and FN-TPB the same conclusions drawn in our previous work on
FN-PCz: (i) the three compounds in solution are suspected to
undergo aggregation/association in their ground state
independently from the nature of the solvent; (ii) Similar to FN-PCz,
the aggregation/association by means of intermolecular or solute-
solvent H-bonds and/or π-stacking interactions should strongly
impact the position and intensity of the LEB 7.
2.5.3 Impact of ground state aggregation: old versus fresh
solutions. The above assumptions find direct confirmation when
comparing the old (1 month for FN-TPA and FN-PCz, and 5 months
for FN-TPB) with the fresh THF solutions of the FN derivatives
(Figure 3 (d)). Indeed, it can be observed from the figures that the
LEB is absent in the old (1 month) THF solutions of FN-TPA and FN-
PCz, compared to the spectra of the fresh THF solutions.
Interestingly, the absorption of the 1 month old THF solution of FN-
TPB is completely identical to that of the fresh solution; however,
the LEB of FN-TPB disappears and the bands at 350-370 nm become
less pronounced in the spectrum of the 5-months solution.
These intriguing observations are consistent with the supposed
presence of the ground state aggregation/association in the fresh
solutions: with the disappearance of the aggregates and the H-
bonds, the related LEB redshift- and intensity-decrease also
disappear, resulting in an old-solution LEB being closer to the HEB
and more intense as compared to the fresh-solution LEB, as
predicted by the theoretical spectra (Figure 3 (c) and Figure S3). The
slower dissociation of FN-TPB aggregates in THF solution (5 months
instead of 1) suggests stronger aggregation tendency for this
compound, which is consistent with the larger charge mobility
observed for this compound (Annex I, SI) and the larger TID (Table
1). We hypothesize that this stronger aggregation efficiency for FN-
TPB can be due to additional intermolecular (Ph)C-H…..π-
interactions involving the phenyl rings of the TPB moiety.
Figure 4. (a) Energy diagram corresponding to the evolution of n-π*,
π-π*CT, π-π*, and D–A transitions of compounds FN-TPA, FN-TPB
and FN-PCz (TD-BMK/6-31G level in gas phase). The oscillator
strengths for the corresponding S0→Si transitions are indicated in
parentheses. (b) Representation of the hole (below arrows) and
electron (over arrows) natural transition orbitals (NTO)
corresponding to the π-π*CT, π-π*, n-π*, and D–A excited states of
compounds FN-PCz, FN-TPB, FN-TPA (BMK/6-31G level in gas
phase). In all cases, the hole- and electron distributions shown here
contribute by roughly 99% to the corresponding excited states.
2.5.2 Impact of the solvent polarity and H-bonds. Absorption
spectra of fluorenone derivatives were accessed for the solutions in
solvents of different polarity and nature as well (Figure 3 (e-g)). The
As for the disappearance of the LEB with time, it was shown in our
recent work 7, that the complete solubilization (producing free-of-
H-bonds/ π-stacking FN-based molecules in THF) can be accelerated
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by sonication and slight increase in solvent polarity. Indeed, needed for the disappearance of the LEB from the absorption
sonication along with gradual heating of the THF solutions of the spectra of THF solution of FN-TPB (Figure 3 (d)) also supports the
three compounds was found to greatly accelerate the hypothesis on the stronger intermolecular interactions in the case
disaggregation process (12-48h; Figure S4) comparing to the of this compound (detailed discussion of the possible types of
spontaneous aging effect (1-5 months).
intermolecular interactions is presented in Annex II, SI). We are
consequently led to speculate that the stronger intermolecular
interactions in the case of FN-TPB apparently translate in enhanced
intermolecular PL quenching as compared to FN-TPA and FN-PCz,
which is at odds with the generally observed AIEE phenomena. The
increase of the FN-TPB PLQY in zeonex by two times as compared to
hexane (0.31 and 0.66 respectively, Table 2) also supports the
hypothesis that the PL quenching in the case of this compound
cannot be of intramolecular origin.
2.6 Photoluminescence properties
Photoluminescence spectra of the studied compounds, recorded in
various media i.e. fresh dilute liquid and solid solutions and neat
films are displayed in Figure 5 (a, b} and in Figure S5. Upon
excitation at 350 nm all fresh solutions and solid state media of our
fluorenone derivatives emit light in yellow spectral region (Figure 5
(c)), with PLQY values depending on the solvent polarity.
Finally, the quenching effect in these compounds was quantified by
2.6.1 Non-polar solvents. PL spectra of FN-TPB and FN-PCz
solutions in hexane and zeonex solutions feature clearly resolved
vibronic structure and are less broad as could be expected for a
typical excimeric emission profile. These properties clearly point to
the intramolecular origin for the emission of the solutions of these
compounds in non-polar solvents.
the determination of the fractional weight of the radiative (Γ) and
2,36
non-radiative (kNR) decay rates:
smaller radiative (0.04 cm-1)
versus non-radiative (0.08 cm-1) rate constants were found for FN-
TPB (Table S2), as compared to the opposite trends found for FN-
TPA and FN-PCz. We suggest consequently that the intermolecular
quenching mechanism in the case of FN-TPB constitutes the
dominant deactivation channel comparing to the intramolecular
one.
The conclusion on the intramolecular origin of the yellow color of
our compounds seems to be also supported by the governing
relaxation pathway. To this aim, photoluminescence decay
transients of the three compounds were recorded for the liquid and
solid solutions, as well as for the neat films (Table 2). The emission
decays of the hexane and solid zeonex solutions were found to be
best fitted by a monoexponential mode exhibiting PL lifetimes
ranging 5.71-9.53 ns. While no direct assignment to the
intramolecular origin can be concluded from this last result, a single
origin for the emission spectra of the three compounds can be
deduced. In view of the well resolved vibronic structure of the
emission profiles, single intramolecular origin and absence of
excimeric contribution can be safely deduced for the emission
spectra of these compounds dispersed in non-polar environments.
Despite the above similarities, differences between PLQY of these
compounds can be observed (Table 2). FN-TPA and FN-PCz
exhibited much higher PLQY of 0.76 and 0.82 in dilute hexane
solution as compared to FN-TPB (0.31). In turn, two-fold increase in
PL efficiency is observed for the solid solution of FN-TPB in rigid
Zeonex matrix, while only insignificant enhancement of η was
observed for FN-TPA and FN-PCz.
In order to obtain more insight on the reasons for these differences,
we focus firstly on the intramolecular phenomena by considering
the energy diagram of the excited states shown in Figure 4 (a). This
diagram suggests for the lowest excited state of all compounds a π-
π*CT transition, which is totally localized on the central part of the
bridge (Figure 4). Similar PLQY of the solutions in hexane should
consequently be expected for the three compounds. However,
while this assumption seems to be verified by the similar PLQY of
0.76 and 0.82 in the case of FN-TPA and FN-PCz, respectively (Table
2), much lower PLQY of 0.31 is deduced for FN-TPB, thus suggesting
for these differences intermolecular origin.
The above hypothesis on the particular behavior of FN-TPB seems
to corroborate with the stronger intermolecular interactions in the
films of this compound as compared to FN-TPA and FN-PCz, which
was deduced from the thermal and charge transport properties
(section 2.2 and Annex I, SI). The much longer disaggregation time
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old THF solutions of these compounds: the intensity increases by up
to 2.3*106 times, whereas the PLQY increases from 0.01 in fresh
THF till 0.22 and 0.35 for FN-TPA and FN-PCz, respectively.
Importantly, the emission-color turns from (almost totally
quenched) yellow to bright blue (Figure 5 (c)), which is unexpected
for this type of fluorenone-based compounds.
Differences in PLQY are again observed for the solutions of FN-TPA
and FN-PCz, on the one hand, and FN-TPB solution, on the other
hand: while PLQY of FN-TPA and FN-PCz drastically drop to 0.01 in
THF, PLQY of FN-TPB increases from 0.31 for the solution in hexane
to 0.56 for THF solution.
Intriguingly, no emission blue-shift was observed for 1 month old
FN-TPB solution (Figure 5 (a, b)). Instead, the intesity of the yellow
band increased twice, and only a small-intensity blue band was
detected. However, the five month old FN-TPB solution in THF
revealed clear- and intense blue emission with PLQY of 0.30.
Disaggregation mechanism and interpretation of PL spectra. These
intriguing results cannot be explained in the frame of
intramolecular interaction, as this was discussed in details in the
7
case of FN-PCz . In order to explain these results, we focus on the
intermolecular interactions through GS aggregation and H-bonds.
At this respect, we remember that C=O…..H-C(Ph) H-bonds are
present in the aggregates of these materials 37–39 which were found
to be responsible for the appearance of the weak, broad, and
shapeless LEB and of the yellow color of FN-PCz in nonpolar media.
7
The total PL quenching of FN-PCz in fresh THF solution was
explained by the occurrence of the hydrogen-bonding dynamic
40,41
quenching (HBDQ) mechanism
. We also remember that the
HBDQ mechanism supposes efficient PL quenching by means of the
H-bond vibrational modes provided that geometrical reorganization
in the excited state is possible. The later condition seems to be
absent in the strongly bound aggregates (hexane solutions, neat
films, or zeonex solid solutions), given the high PLQYs measured for
the solutions of FN-TPA and FN-PCz in hexane (0.76 and 0.82,
respectively). In this frame, the strong PL quenching in fresh THF
solutions suggests the presence of an intermediate state between
the strongly bound aggregates (initial state), and the free FN-TPA
(FN-PCz) molecules (final state). This intermediate state should
consequently correspond to species satisfying three experimental
observations: (i) being obtained very fast (upon THF solution
preparation), (ii) corresponding to species bonded loosely enough
to allow facile intermolecular geometry reorganizations and
switching-on of the HBDQ mechanism (total quenching in THF), and
(iii) corresponding to species bonded strongly enough to resist to
dissociation for long time (1-5 months).
Figure
5.
(a)
Normalized
and
(b)
non-normalized
photoluminescence spectra (λex = 350 nm) of old (1 month) and
fresh THF 10-5M solutions of FN-TPA, FN-TPB and FN-PCz. View (c)
of neat films, hexane, fresh and old (5 months) THF solutions of FN-
TPA, FN-TPB and FN-PCz with UV lamp irradiation.
Based on the above requirements, we suggest a two-step-three-
states disaggregation mechanism for these compounds in THF
solvent: (i) fast relaxation-only of the π-π stacked aggregates,
meaning presence of loosely bound aggregates (step 1), followed by
(ii) slow demolition of the loosely bound aggregates and of the H-
bonds (step 2), according to the following scheme:
2.6.2 Polar solvents. Here we discuss the effect of the polarity in
the PL properties of the compounds and suggest a mechanism for
their disaggregation in THF.
Old versus fresh solutions. PL spectra of old THF solutions of FN
derivatives exhibit only one PL band at ca. 450-470 nm, as
compared to two emission bands in the normalized PL spectra of
fresh solutions. In direct correlation with the disappearance of LEB
in the spectra of old THF solutions, time-dependent position and
intensity alteration was observed in the PL spectra of our FN
derivatives as well (Figure 5 (a, b)). While totally quenched emission
in yellow region was detected for the fresh THF solutions of FN-TPA
and FN-PCz, drastic PL enhancement was revealed for the 1 month
(Strongly bound aggregates) ꢀ (Loosely bound aggregates) ꢀ (Free
molecules)
The presence of the initial and final states is demonstrated
experimentally by the presence- and absence of the LEB in the
spectra of hexane and old THF solutions respectively (Figure 3 (d)
and our previous study on FN-PCz 7). The fast observation of the
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intermediate species (loosely bound aggregates) can be explained immediate charge (dipole) stabilization, in reduction of the
by the electrostatic effects in the polar solvent, resulting in intermolecular electrostatic interactions, and in increase of
Table 2. Photoluminescence quantum yields, decay lifetimes and triplet energies of FN-TPA, FN-TPB and FN-PCz.
10-5
solution
η a
Hexane 10-5 THF
10-5 THF
Zeonex film
Neat film
solution (fresh)
solution (old)
Compound
FN-TPA
τ b [ns]
η a
τ b [ns]
η a
τ b [ns]
η a
τ b[ns]
ETc [eV]
η a
τ b [ns]
0.83 [24.5%]
2.19 [56.2%]
5.68 [19.3%]
0.70 [54.6%]
1.66 [35.5%]
6.56 [9.90%]
0.81 [34.3%]
2.58 [47.7%]
7.41 [18.0%]
2.55 [66.56%]
7.75 [33.44%]
0.76
0.31
0.82
5.71
0.01
2.78
0.22
0.85
7.13
9.53
2.62
0.14
2.65 [37.58%]
6.26 [62.42%]
FN-TPB
8.31
0.56
7.79
0.30
0.66
2.62
0.22
1.47 [17.31%]
7.27 [41.82%]
26.18 [40.87%]
FN-PCz
8.24
0.01
1.68
0.35
0.90
9.20
2.68
0.16
a
b
Photoluminescence quantum yields estimated with the usage of the integrating sphere. Photoluminescence decay lifetimes (χ2 in the
range 1.00-1.13). c Determined from the half blue-edge onset of the phosphorescence spectra recorded for the solid solutions in polymer
(Zeonex) matrix at 77K.
intermolecular distances. Accordingly, easier intermolecular PCz and FN-TPA, respectively, as compared to 7.79 ns for FN-TPB.
geometry reorganization can be expected in this intermediate state, Additionally, clear presence of vibronic structure can be observed in
which we speculate to result in total PL quenching by means of the emission spectra of fresh and 1 month old solutions of FN-TPB.
HBDQ mechanism. In the case of FN-TPB corresponding to stronger While the PL lifetime and vibrational progression profile of the fresh
intermolecular interactions as compared to FN-TPA and FN-PCz, this solution of FN-TPB in THF is similar to that of the solution in hexane
electrostatic effect is obviously relatively small as compared to (7.79 ns and 8.31 ns respectively), thus suggesting similar
other sources of intermolecular interactions. Accordingly, intramolecular nature of the emissive species from aggregates, the
insufficient intermolecular geometry relaxations can be deduced for PL lifetimes of THF solutions of FN-PCz and FN-TPA are by 2-4 times
FN-TPB dispersed in THF, preventing from facile reorganization of shorter as compared to the hexane ones (Table 2). The total
the C=O…..H-C(Ph) H-bonds in the excited state and from switching- quenching and the very short PL lifetime for FN-PCz and FN-TPA
on the HBDQ mechanism.
indicate a very fast deactivation channel, faster than the
Finally, the very slow demolition of the loosely bound aggregates intramolecular radiative one. Both PLQY and PL lifetime changes
(step 2) can be explained by the strong intermolecular interactions from hexane to fresh THF solution consequently suggest that the PL
of several tenths of kcal/mol (our calculations for dimers of FN-PCz), lifetimes of 2.78 ns and 1.68 ns for FN-TPA and FN-PCz respectively
in turn stemming from π-π stacking and different types of H-bonds correspond to non-radiative deactivation channels, which we
(see Annex III, SI). This explanation seems consistent with previous suppose to correspond to H-bond dynamical quenching mechanism
studies reported on the very strong tendency for aggregation in (HBDQ), operating in the loosely bound aggregates in THF.
42
naphthalene and perylene diimide based compounds.
These As a means to provide additional support to the above analysis, we
strong intermolecular interactions in the aggregates, along with the have performed PL lifetime measurements for the old blue-emitting
slow diffusion necessary for the dissociated molecules to escape solutions. Interestingly, three exponential modes were necessary to
from the aggregate surface, could explain the slow process of total fit the decay profiles (Table 2), corresponding to very short (0.70-
solubilization of these compounds in THF. The important 0.83 ns), intermediate (1.66-2.58 ns), and somewhat longer
acceleration of the total solubilization obtained by means of lifetimes (5.68-7.41 ns). These last results provide a nice support to
sonication (Figure S4) seems to support the proposed mechanism, the mechanisms proposed in the above analysis. Indeed: (i) the
assumedly by helping mechanically to the destabilization of the π-π longer lifetimes decays of old THF solutions (5.68-7.41 ns) are
stacking interactions of the surficial molecules and/or by similar to the intramolecular emission lifetimes in hexane (5.71-8.31
accelerating their diffusion.
ns), thus corresponding to the intramolecular non-quenched PL of
As for the increase of PLQY of FN-TPB from 0.31 (hexane) to 0.56 the aggregated state. (ii) the intermediate lifetimes of 1.66-2.58 ns
(THF), we suggest this to stem from the decreased intermolecular are similar to those obtained for the fresh solutions of FN-TPA and
PL quenching due to the slightly increased intermolecular FN-PCz in THF (1.68-2.78 ns), and can be attributed to the non-
separation in THF (less important as compared to FN-TPA and FN- radiative decay channels in the aggregates. (iii) The sub-nanosecond
PCz).
component (0.70-0.83 ns) found for the old THF solutions, which is
PL decay modes in THF solutions. The above two-step-three-states absent in the PL decays of fresh solutions, corresponds to the new
mechanism is supported by the differences observed in the PL non-aggregated free from H-bonds blue-emitting species. The faster
decay modes and the emission band profiles of the solutions of intramolecular radiative deactivation of free-of-H-bond species in
three compounds in THF. Indeed, monoexponential decay modes the old solutions as compared to the fresh THF or hexane solutions
were found for the fresh THF solutions of the three compounds, yet is consistent with the larger oscillator strengths deduced from the
much shorter PL lifetimes of 1.68 ns and 2.78 ns were found for FN- theoretical calculations (Figure 4 (a)). An equilibrium between three
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types of species in THF solutions, corresponding to aggregated-, are necessary to fit the PL decay profiles in the case of FN-TPA and
loosely bound aggregates, and free-of-H-bond species can FN-TPB, with one fast component (2.55 ns and 2.65 ns,
consequently be safely concluded.
respectively), and one slower component (7.75 ns and 6.26 ns,
There is however an intriguing observation: the longer lifetime respectively). While the slower component (ca. 6-8 ns) correlates
species characteristic of hexane solutions (5.71-8.31 ns, initial state) with the decay data observed for non-polar media, pointing at the
and old THF solutions (5.68-7.41 ns, final state,), were not observed emissive intramolecular π-πCT origin, the fast component (ca. 2.5 ns)
in the fresh THF solutions (intermediate state). We speculate that can be attributed to the non-radiative decay by means of HBDQ.
these species in the old THF solutions (“final” state) correspond to Finally, a third exponential mode is necessary to fit the FN-PCz PL
small mono-columnar aggregates (absence of inter-column H- decay profile with fairly long lifetime of 27.18 ns, very probably
bonds), stemming from the demolition of poly-columnar aggregates corresponding to excimer formation or to energy transfer via
(presence of inter-column H-bonds). This scenario is also consistent exciton migration through the localized states in disordered media
with the easier breaking of H-bonds due to their less important such as neat amorphous films 43,44. However, this third component
interaction energy as compared to π-π stacking ones (see Annex IV, constitutes roughly 41% of the total radiation (Table 2), the
SI), and with the dominant red-shifting impact of the H-bonds on dominant radiation channel being again the intramolecular one.
the LEB as compared to the π-stacked aggregates7.
To further support the ability of the derivatives for aggregation, we We finally discuss the impact of temperature on the PL properties
conducted solvent/non-solvent photoluminescence test, the of FN-compounds. Dodecane was chosen as a non-polar solvent
results of which are discussed in detail in Annex V, SI. instead of hexane due to low dielectric constant (ε = 2.00) and high
All these data collectively support our two-step-three-state model boiling point (216.2 oC). Figure 6a indicates that the emission
for the emissive behavior of these compounds: intensity of the yellow band increases upon temperature increase.
(i) non-polar media: presence of aggregated species strongly The PL intensity enhancement decreases in the order FN-TPA (~5
emitting in the yellow region (absence of HBDQ). times) > FN-TPB (~3 times) > FN-PCz (~2 times). Additionally, a slight
2.6.4 Temperature dependence.
a
(ii) fresh THF solutions: relaxation of the aggregates (first-step) due blue-shift can be observed in the position of the 0-1 transitions of
to the electrostatic stabilization induced from the polar solvent. The FN-TPA and FN-TPB, whereas no shift can be observed in the case
emission in these loosely bound aggregates is strongly quenched by of FN-PCz. These observations can be explained by different factors,
means of HBDQ mechanism.
including weakening of the aggregation and/or H-bond efficiencies,
(iii) old THF solutions: demolition of the loosely bound aggregates resulting in increasing of the LEB intensity and/or reducing of
7
and breaking of H-bonds (second step), producing free-of-H-bonds HBDQ, respectively. On the other hand, possible singlet→triplet
molecules. Accordingly, the LEB and the emissive S1 state are and triplet→singlet ISC at different levels cannot be excluded.
shifted to the blue region, and the HBDQ mechanism is absent, However, smaller PL enhancement was observed for the solid
resulting in drastic PL intensity increase.
solutions in zeonex upon temperature increase (by roughly 1.2, 1.4,
2.6.3 Neat films. The emission spectra of the neat films present an and 1.2 times for FN-TPA, FN-TPB, and FN-PCz respectively Figure 6
intermediate situation between hexane and THF solutions. Indeed, (b)), that we correlate with the smaller degree of aggregation in
while intermediate redshift of the emission between hexane and solid solutions, hence with the presence of a larger number of free
THF is obtained, consistent with the intermediate polarity of the molecules. This is similar to the effect observed in the case of FN-
neat films, the vibrational structure of the spectra of neat films is PCz in THF:7 negligible temperature impact was observed on the
lost in the three cases. Importantly, PLQYs ranging from 0.14 to 0.22 blue band (free molecules, left-hand shoulder in Figure 6 (c)),
are much smaller than those of hexane or zeonex solutions. We despite the large intensity enhancement observed for the PL yellow
hypothesize that both aggregated and non-aggregated molecular band. The almost absence of temperature effect on the emission of
species are present in the neat films, thus reducing PLQY and de- free molecules seems consequently to rule out any important
structuring the PL profiles as compared to those of the solutions in contribution from the ISC mechanism, thus giving confidence to the
hexane and zeonex. This hypothesis seems to be supported by the hypothesis on the dominant impact of aggregation/H-bond
PL decay measurements (Table 2). Indeed, two exponential modes efficiency
weakening.
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Figure 6. Photoluminescence spectra of the solutions of FN-TPA, FN-TPB and FN-PCz (a) in dodecane (10-5M), and (b) in Zeonex films.
recorded at various temperatures. Inserts correspond to the dependence of PL maxima intensity on the temperature. (c) Temperature
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effect on the PL spectra of FN-PCz for fresh 10-5 M THF solutions, Reproduced with permission from the editors. Copyright © 2016,
American Chemical Society.
1
2
J. E. Kuder, J. Electrochem. Soc., 1978, 125, 1750.
T. Matulaitis, N. Kostiv, J. V. Grazulevicius, L. Peciulyte, J.
Simokaitiene, V. Jankauskas, B. Luszczynska and J. Ulanski,
Dye. Pigment., 2015.
Conclusions
Multichromophore fluorenone-centered compounds were
designed, synthesized and characterized. The new fluorenone-
based compounds exhibit outstanding thermal stability,
ambipolar charge transport with hole and electron mobilities
exceeding 10-3 cm2/Vs,and photoluminescence quantum yields
reaching 0.9 in non-polar media. The optical properties of THF
solutions were intriguingly found to change drastically after 1-
5 months: the absorption low-energy-band disappears, their
emission color changes from yellow to blue, and their emission
intensity increases by 106 times.
3
4
5
6
7
S. Roquet, A. Cravino, P. Leriche, O. Alévêque, P. Frère and
J. Roncali, J. Am. Chem. Soc., 2006, 128, 3459–66.
Y. Jiang, Y. Wang, J. Hua, J. Tang, B. Li, S. Qian and H. Tian,
Chem. Commun. (Camb)., 2010, 46, 4689–91.
Y. Liu, X. Tao, F. Wang, X. Dang, D. Zou, Y. Ren and M. Jiang,
J. Phys. Chem. C, 2008, 112, 3975–3981.
S.-J. Su, Y. Takahashi, T. Chiba, T. Takeda and J. Kido, Adv.
Funct. Mater., 2009, 19, 1260–1267.
N. A. Kukhta, D. A. da Silva Filho, D. Volyniuk, J. V.
Grazulevicius and G. Sini, Chem. Mater., 2017, 29, 1695–
1707.
These observations are due to the strong tendency of these
compounds to form aggregates in their ground state, which
resist to fast solubilisation in almost all habitual nonpolar and
polar solvents. Demolition of these aggregates in THF is
suggested to operate in two steps: fast relaxation of the
aggregates resulting in loosely bound agregates, followed by
very slow demolition (1-5 months) of the later ones. Sonication
is found to importantly accelerate this demolition.
8
9
X.-H. Zhou, Y. Zhang, Y.-Q. Xie, Y. Cao and J. Pei,
Macromolecules, 2006, 39, 3830–3840.
K. Becker, J. M. Lupton, J. Feldmann, B. S. Nehls, F.
Galbrecht, D. Q. Gao and U. Scherf, Adv. Funct. Mater.,
2006, 16, 364–370.
10
E. Zojer, A. Pogantsch, E. Hennebicq, D. Beljonne, J.-L.
Brédas, P. Scandiucci de Freitas, U. Scherf and E. J. W. List,
J. Chem. Phys., 2002, 117, 6794–6802.
Inherently to these aggregates, CO...HC(Ph) H-bonds are
established, which redshift importantly the absorption low-
energy-band and the emission spectra, and reduce their
11
12
13
H. Weingarten, J. Org. Chem., 1964, 29, 977–978.
S. H. Tucker, J. Chem. Soc., 1926, 129, 546.
D. Rajwar, X. Sun, S. J. Cho, A. C. Grimsdale and D. Fichou,
CrystEngComm, 2012, 14, 5182.
intensity. The slow evolution from these
π-stacked- and H-
bonded aggregates in free molecules results in evolution of the
emission color from yellow to blue, with drastic intensity
increase. The results indicate that the time needed for yellow-
to-blue color swapping depends on the aggregation strength
and can be tuned by structural modifications, whereas the
color swapping and PL efficiency only depend on the presence-
and strength of the intermolecular H-bonds.
14
15
16
S. W. Kim, S. C. Shim, B.-J. Jung and H.-K. Shim, Polymer
(Guildf)., 2002, 43, 4297–4305.
D. H. Cho, J. H. Lee and B. H. Kim, J. Org. Chem., 1999, 64,
8048–8050.
N. A. Kukhta, D. Volyniuk, L. Peciulyte, J. Ostrauskaite, G.
Juska and J. V. Grazulevicius, Dye. Pigment., 2015, 117,
122–132.
The aggregation/association in the ground state of these
compounds is also found to induce a temperature dependence
in the optical properties of these compounds: upon
temperature increase, an unusual photoluminescence
intensity enhancement by up to five times was detected for
these compounds dispersed in non-polar media, dominantly
originating from the weakening of the HBDQ mechanism
inherent to C=O…H-C hydrogen-bonds.
17
18
I. A. Khotina, L. S. Lepnev, N. S. Burenkova, P. M. Valetsky
and A. G. Vitukhnovsky, J. Lumin., 2004, 110, 232–238.
T. L. (Theodore L. Brown, H. E. (Harold E. LeMay, B. E.
Bursten, C. J. (Catherine J. Murphy, P. M. Woodward and
M. Stoltzfus, Chemistryꢀ: the central science, .
K. R. Justin Thomas, J. T. Lin, Y.-T. Tao and C.-W. Ko, J. Am.
Chem. Soc., 2001, 123, 9404–9411.
19
20
N. Metri, X. Sallenave, C. Plesse, L. Beouch, P.-H. Aubert, F.
Goubard, C. Chevrot and G. Sini, J. Phys. Chem. C, 2012,
116, 3765–3772.
21
22
23
B. C. Lin, C. P. Cheng and Z. P. M. Lao, J. Phys. Chem. A,
2003, 107, 5241–5251.
M. Malagoli and J. L. Brédas, Chem. Phys. Lett., 2000, 327,
13–17.
Acknowledgements
GS gratefully thanks the calculation center of Cergy-Pontoise
University for computing time and technical support, and Dr.
V. Coropceanu (Georgia Tech, Atlanta, USA) for the stimulating
discussions.
V. Vergadou, G. Pistolis, A. Michaelides, G. Varvounis, M.
Siskos, N. Boukos and S. Skoulika, Cryst. Growth Des., 2006,
6, 2486–2492.
24
O. Kwon, S. Barlow, S. A. Odom, L. Beverina, N. J.
This journal is © The Royal Society of Chemistry 20xx
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Page 16 of 17
View Article Online
DOI: 10.1039/C7TC05798A
ARTICLE
Journal Name
Thompson, E. Zojer, J.-L. Brédas and S. R. Marder, J. Phys.
Chem. A, 2005, 109, 9346–52.
25
26
27
L. A. Estrada, J. E. Yarnell and D. C. Neckers, J. Phys. Chem.
A, 2011, 115, 6366–75.
I. Reche, I. Gallardo and G. Guirado, New J. Chem., 2014,
38, 5030–5036.
B. R. Kaafarani, A. O. El-Ballouli, R. Trattnig, A. Fonari, S.
Sax, B. Wex, C. Risko, R. S. Khnayzer, S. Barlow, D. Patra, T.
V. Timofeeva, E. J. W. List, J.-L. Brédas and S. R. Marder, J.
Mater. Chem. C, 2013, 1, 1638.
28
29
30
A. Tigreros, V. Dhas, A. Ortiz, B. Insuasty, N. Martín and L.
Echegoyen, Sol. Energy Mater. Sol. Cells, 2014, 121, 61–68.
G. L. Eakins, J. S. Alford, B. J. Tiegs, B. E. Breyfogle and C. J.
Stearman, J. Phys. Org. Chem., 2011, 24, 1119–1128.
R. R. Reghu, J. V. Grazulevicius, J. Simokaitiene, T.
Matulaitis, A. Miasojedovas, K. Kazlauskas, S. Jursenas, P.
Data, M. Lapkowski and P. Zassowski, Dye. Pigment., 2013,
97, 412–422.
31
32
N. A. Kukhta, D. Volyniuk, J. V. Grazulevicius and G. Juska, J.
Phys. Chem. C, 2016, 120, 1208–1217.
V. Mimaite, J. V. Grazulevicius, R. Laurinaviciute, D.
Volyniuk, V. Jankauskas and G. Sini, J. Mater. Chem. C,
2015, 3, 11660–11674.
33
P. Baronas, K. Kazlauskas, A. Gruodis, V. Jankauskas, A.
Tomkeviciene, J. Simokaitiene, J. Vidas Grazulevicius and S.
Jursenas, J. Lumin., 2016, 169, 256–265.
34
35
K. Yoshihara, J. Chem. Phys., 1966, 45, 1991.
L. Giribabu and K. Sudhakar, J. Photochem. Photobiol. A
Chem., 2015, 296, 11–18.
36
37
C. Albrecht, Anal. Bioanal. Chem., 2008, 390, 1223–1224.
M.-S. Yuan, D.-E. Wang, P. Xue, W. Wang, J.-C. Wang, Q.
Tu, Z. Liu, Y. Liu, Y. Zhang and J. Wang, Chem. Mater., 2014,
26, 2467–2477.
38
39
F. Würthner, Chem. Commun., 2004, 122, 1564–1579.
J. Xu, S. Semin, D. Niedzialek, P. H. J. Kouwer, E. Fron, E.
Coutino, M. Savoini, Y. Li, J. Hofkens, H. Uji-I, D. Beljonne,
T. Rasing and A. E. Rowan, Adv. Mater., 2013, 25, 2084–9.
V. Samant, A. K. Singh, G. Ramakrishna, H. N. Ghosh, T. K.
Ghanty and D. K. Palit, J. Phys. Chem. A, 2005, 109, 8693–
8704.
40
41
42
G.-J. Zhao and K.-L. Han, J. Phys. Chem. A, 2007, 111, 2469–
2474.
R. Steyrleuthner, M. Schubert, I. Howard, B. Klaumünzer, K.
Schilling, Z. Chen, P. Saalfrank, F. Laquai, A. Facchetti and
D. Neher, J. Am. Chem. Soc., 2012, 134, 18303–18317.
R. Karpicz, S. Puzinas, S. Krotkus, K. Kazlauskas, S. Jursenas,
J. V Grazulevicius, S. Grigalevicius and V. Gulbinas, J. Chem.
Phys., 2011, 134, 204508.
43
44
T. Serevičius, P. Adomėnas, O. Adomėnienė, R. Rimkus, V.
Jankauskas, A. Gruodis, K. Kazlauskas and S. Juršėnas, Dye.
Pigment., 2013, 98, 304–315.
16 | J. Name., 2012, 00, 1-3
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Fluorenone derivatives demonstrate bright blue emission instead of yellow due to the
disruption of the intermolecular CO…HC (aromatic) hydrogen bonds.