Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

Article abstract of DOI:10.3762/BJOC.16.139

Herein, we present a facile synthesis of three azide-functionalized fluorophores and their covalent attachment as triazoles in Huisgen-type cycloadditions with model alkynes. Besides two ortho- and para-bromo-substituted benzaldehydes, the azide functionalization of a fluorene-based structure will be presented. The copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) of the so-synthesized azide-functionalized bromocarbaldehydes with terminal alkynes, exhibiting different degrees of steric demand, was performed in high efficiency. Finally, we investigated the photophysical properties of the azide-functionalized arenes and their covalently linked triazole derivatives to gain deeper insight towards the effect of these covalent linkers on the emission behavior.

Full text of DOI:10.3762/BJOC.16.139

Clickable azide-functionalized bromoarylaldehydes –
synthesis and photophysical characterization
Dominik Göbel1, Marius Friedrich1,2, Enno Lork3 and Boris J. Nachtsheim*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2020, 16, 1683–1692.
1Institute for Organic and Analytical Chemistry, University of Bremen,
Leobener Straße 7, 28359 Bremen, Germany, 2Department of
Organic Chemistry, Technical University Kaiserslautern,
Erwin-Schrödinger-Straße Geb.54, 67663 Kaiserslautern, Germany
and 3Institute for Inorganic and Crystallographic Chemistry, University
of Bremen, Leobener Straße NW2, 28359 Bremen, Germany
doi:10.3762/bjoc.16.139
Received: 11 May 2020
Accepted: 30 June 2020
Published: 14 July 2020
This article is part of the thematic issue "C–H functionalization for
materials science".
Email:
Boris J. Nachtsheim* - nachtsheim@uni-bremen.de
Guest Editor: K. Itami
* Corresponding author
© 2020 Göbel et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
bromoarylaldehydes; click-chemistry; fluorenes; fluorescence;
phosphorescence
Abstract
Herein, we present a facile synthesis of three azide-functionalized fluorophores and their covalent attachment as triazoles in
Huisgen-type cycloadditions with model alkynes. Besides two ortho- and para-bromo-substituted benzaldehydes, the azide functio-
nalization of a fluorene-based structure will be presented. The copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) of the
so-synthesized azide-functionalized bromocarbaldehydes with terminal alkynes, exhibiting different degrees of steric demand, was
performed in high efficiency. Finally, we investigated the photophysical properties of the azide-functionalized arenes and
their covalently linked triazole derivatives to gain deeper insight towards the effect of these covalent linkers on the emission behav-
ior.
Introduction
Small organic luminophores exhibiting room-temperature phos- cence) takes place without a change in the electron spin, phos-
phorescence (RTP) have attracted great attention due to promis- phorescence is defined as the radiative transition from the
ing applications in optoelectronic devices [1-8], biological lowest excited triplet state (T1) to the singlet ground state (S0)
imaging [9-12] and chemical sensing [13-15]. Referring to the [18-21]. Triplet state excitons are generated by the spin-
Jablonski diagram (see Scheme 1a) [16,17], upon excitation forbidden intersystem crossing (ISC) process from the first
from the singlet ground state (S0) to higher singlet states (Sn), excited singlet state (S1). Pursuant to the El-Sayed rule (see
followed by internal conversion (IC), either non-radiative or Scheme 1b) [22,23], ISC is spin allowed from 1(n,π*) to 3(π,π*)
radiative decay to S0 can occur. While the latter decay (fluores- and from 1(π,π*) to 3(n,π*) excited states, while ISC is spin-
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charge-transfer (ICT) interactions is an approved method
[48,49]. (2) Significant reduction of non-radiative transitions
can be achieved by the host–guest method [50-52] or by crystal-
lization [53-57]. In difference to the liquid phase, the highly
ordered packing and the restriction of molecular motions in the
crystalline state favor a persistent luminescence.
The promotion of ISC processes through intermolecular
halogen bonding to generate efficient RTP was initially investi-
gated by Kim et al. [58]. They developed the minimalistic 2,5-
dihexyloxy-4-bromobenzaldehyde (1) [59-63] which showed a
weak fluorescence in solution, but exhibited a green phospho-
rescence with a quantum yield of ΦP = 2.9% in the crystalline
state: this behavior was caused by intermolecular halogen bonds
from the carbonyl-oxygen atom to an adjacent bromine atom
(Figure 1a).
Despite multifarious examples of RTP in the crystalline state,
purely organic compounds showing RTP in solution are rare
[64-69]. Takeuchi et al. [28] reported a bromofluorenecarbalde-
hyde 2 which shows blue fluorescence in chloroform at 298 K
under air and green phosphorescence under argon with a phos-
phorescence quantum yield of ΦP = 5.9% (Figure 1b). This ob-
servation is reasoned by a strong (π,π*) character of the T2
state.
Although phosphorescent organic compounds are well investi-
gated with respect to their photophysical properties in the crys-
talline state, in solution or physically embedded in polymer
matrices, there is a significant lack of possibilities [61] for their
Scheme 1: a) Schematic depiction of the Jablonski diagram.
b) Schematic representation of El-Sayed’s rule.
forbidden from 1(n,π*) to 3(n,π*) and from 1(π,π*) to 3(π,π*) targeted covalent attachment to higher structures. This is due to
excited states, owing to the poor orbital overlap, resulting in a missing synthetic strategies to incorporate suitable linkable
decreased spin-orbit coupling.
functionalities into those luminophores.
Quenching processes of triplet states, induced by molecular Our group is highly interested in the de novo synthesis of small
motions, oxygen, or humidity, restrict the versatile application organic luminophores and in this regard, we recently developed
of such organic materials [24]. Thus, low temperatures [25-27] efficient methods for the synthesis of ESIPT-based
or inert conditions [28] are necessary to facilitate an afterglow luminophores [70-72]. Herein, we present the efficient functio-
emission.
nalization of derivatives of the potent luminophores 1 and 2
with “clickable” azide functionalities to target the structures 3–5
Most phosphorescence studies are focused on metal complexes and further investigated the influence of this functionalization,
due to a strong heavy atom-induced spin-orbit coupling [29-33]. both in the unlinked azide state and the linked triazole state, on
Considering the high price and the toxicity of many metal com- the emission properties of these compounds (Figure 1).
plexes, pure organic phosphors are highly desirable [16,17,34-
37]. Two approaches are applied to achieve organic phosphors:
Results and Discussion
Syntheses para- and ortho-bromobenzalde-
(1) introduction of nonmetal heavy atoms, such as halogens (Br
or I) or functionalities containing lone pairs, in particular car-
bonyl groups, nitrogen, sulfur, and phosphorus derivatives hyde 3 and 4
which facilitate the ISC process from S1 to Tn and thus increase We initiated our synthetic investigations towards azide-functio-
the spin-orbital coupling [38-47]. Also, decreasing the nalized para-bromobenzaldehyde 3 with a two-step sequence.
singlet–triplet splitting energy (ΔEST) caused by intramolecular Condensation with 2-amino-2-methylpropan-1-ol and oxidation
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Figure 1: Top: literature examples of organic compounds showing RTP in the crystalline state (a) and in solution (b). Bottom: azide-linked derivatives
presented in this work.
with NBS yielded oxazoline 6 in a good yield. Directed ortho- using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and reaction
metalation utilizing TMPMgCl·LiCl under mild conditions and with diphenylphosphoryl azide (DPPA) in excellent yield.
subsequent smooth formylation with DMF afforded benzalde- Finally, the oxazoline group, which acted as directing and
hyde 7 (see Scheme 2). Due to rapid decomposition of 7 under protecting group, was removed in a three-step sequence of
ambient and acidic conditions, rapid aqueous work-up was con- N-methylation, reduction of the in situ formed iminium ion and
ducted, followed by reduction with NaBH4, yielding the corre- acidic hydrolysis. This afforded the azide-functionalized para-
sponding primary alcohol 8 in 81% yield over two steps. The bromobenzaldehyde 3 in 78% yield and an overall yield of 56%
transformation to azide 9 was accomplished by deprotonation (starting from 4-bromobenzaldehyde).
Scheme 2: Reaction conditions for para-bromobenzaldehyde 3: a) 1) 2-amino-2-methylpropan-1-ol, 4 Å MS, CH2Cl2, 25 °C, 18 h; 2) NBS, CH2Cl2,
25 °C, 5 h, 91%; b) 1) TMPMgCl·LiCl, THF, 25 °C, 4 h; 2) DMF, THF, 0 °C to 25 °C, 1.5 h; c) NaBH4, THF/MeOH 1:1 v/v, 0 °C, 1 h, 81% (2 steps);
d) DPPA, DBU, PhMe, 25 °C, 18 h, 98%; e) 1) MeOTf, CH2Cl2, 25 °C, 2.5 h; 2) NaBH4, THF/MeOH 4:1 v/v, 0 °C, 2.5 h; 3) oxalic acid, THF/H2O
4:1 v/v, 25 °C, 20 h, 78%. Overall yield from 4-bromobenzaldehyde to 3: 56% (5 steps). Reaction conditions for ortho-bromobenzaldehyde 4:
f) 1) 2-amino-2-methylpropan-1-ol, 4 Å MS, CH2Cl2, 25 °C, 18 h; 2) NBS, CH2Cl2, 25 °C, 4 h, 98%; g) 1) TMPMgCl·LiCl, THF, 25 °C, 4 h;
2) (CBrCl2)2, THF, 0 °C to 25 °C, 10 h, 76%; h) NBS, AIBN, CCl4, 100 °C, 7 h, 66%; i) NaN3, DMF, 25 °C, 4 h, 99%; j) 1) MeOTf, CH2Cl2, 25 °C,
2.5 h; 2) NaBH4, THF/MeOH 4:1 v/v, 0 °C, 2.5 h; 3) oxalic acid, THF/H2O 4:1 v/v, 25 °C, 20 h, 85%. Overall yield from 4-methylbenzaldehyde to 4:
41% (5 steps).
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Azide-functionalized ortho-bromobenzaldehyde 4 was pre- Bromofluorenecarbaldehyde 5
pared by a similar route as aldehyde 3. Initially, oxazoline for- The synthetic route to azide-functionalized 7-bromofluorene-2-
mation from 4-methylbenzaldehyde yielded 2-aryloxazoline 10 carbaldehyde 5 started from unfunctionalized fluorene. Double
in almost quantitative yield. The introduction of the ortho- bromination to 14, followed by double methylation of the meth-
bromine substituent was again accomplished by metalation ylene bridge to 15 and a lithiation/formylation sequence
using TMPMgCl·LiCl and subsequent reaction with 1,2-di- afforded 7-bromofluorene-2-carbaldehyde 16 in excellent yield
bromotetrachloroethane to afford 11 in 76% yield. A second over three steps. Conversion to the 2-aryloxazoline 17 was
bromination at the benzylic position provided the dibrominated accomplished in 92% yield using the same method as described
derivative 12 in 66% yield. The substitution reaction of benzyl for the synthesis of 6 and 10. ortho-Metalation with
bromide with sodium azide delivered the primary azide 13 in TMPMgCl·LiCl [70] and conversion of the magnesiated species
quantitative yield. Again, the final back-conversion of the oxa- with DMF to carbaldehyde 18 was followed by reduction with
zoline group to the corresponding aldehyde afforded azide- NaBH4 to give the primary alcohol 19. In contrast to benzalde-
functionalized ortho-bromobenzaldehyde 4 in 85% yield and an hyde 7, carbaldehyde 18 showed no decomposition at ambient
overall yield of 41% (starting from 4-methylbenzaldehyde).
temperature. While acidic hydrolysis of 19 provided exocyclic
Scheme 3: Reaction conditions: a) Br2, Fe powder, CHCl3, 0 °C, 4 h, 99%; b) KOH, KI, MeI, DMSO, 25 °C, 18 h, 92%; c) 1) n-BuLi, THF, ‒78 °C,
1 h; 2) DMF, THF, −78 °C to 25 °C, 10 h, 90%; d) 1) 2-amino-2-methylpropan-1-ol, 4 Å MS, CH2Cl2, 25 °C, 18 h; 2) NBS, CH2Cl2, 25 °C, 3 h, 92%;
e) 1) TMPMgCl·LiCl, THF, 25 °C, 4 h; 2) DMF, THF, ‒15 °C to 25 °C, 2 h; f) NaBH4, THF/MeOH 1:1 v/v, 0 °C, 1.5 h, 79% (2 steps); g) HCl (4 N),
120 °C, 6 h, 91%; h) 1) DPPA, DBU, PhMe, 25 °C, 15 h; 2) NaN3, PhMe, 60 °C, 4 h, 87%; i) 1) MeOTf, CH2Cl2, 25 °C, 2.5 h; 2) NaBH4, THF/MeOH
4:1 v/v, 0 °C, 2.5 h; 3) oxalic acid, THF/H2O 4:1 v/v, 25 °C, 20 h, 86%. Overall yield to 5: 45% (8 steps). The molecular structure of 5 shows 50%
probability ellipsoids.
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γ-lactone 20, the substitution reaction with DPPA/NaN3 yielded Derivatization of fluorenyl methanol 19
the primary azide in 87% yield. In accordance to previous To gain deeper insights into the emission behavior of fluorenes
deprotection reactions, fluorene 21 was converted by means of a bearing different functional groups in the side chains, fluorenyl-
three-step sequence to the desired azide-functionalized methanol 19 was subjected to derivatization reactions (see
7-bromofluorene-2-carbaldehyde 5 in 86% yield and an overall Scheme 4). Deprotonation and subsequent methylation afforded
yield of 45% (starting from fluorene). The molecular structure methoxy derivative 22, which was then converted into the me-
of 5 could be verified by X-ray diffraction (XRD, see thoxy-functionalized 7-bromofluorene-2-carbaldehyde 23 in
Scheme 3).
75% yield. Implementation of potent leaving groups in the side
Scheme 4: Reaction conditions: a) 1) NaH, THF, 0 °C, 30 min; 2) MeI, THF, 0 °C to 25 °C, 2 h, 99%; b) 1) MeOTf, CH2Cl2, 25 °C, 3 h; 2) NaBH4,
THF/MeOH 4:1 v/v, 0 °C, 3 h; 3) oxalic acid, THF/H2O 4:1 v/v, 25 °C, 24 h, 75%. Overall yield from fluorene to 23: 44% (8 steps). c) CBr4, PPh3,
CH2Cl2, 0 °C to 25 °C, 2 h, 95%; or NBS, PPh3, CH2Cl2, 0 °C to 25 °C, 2 h, 91%; or PBr3, CH2Cl2, 0 °C to 25 °C, 2 h, 92%; d) MeOTf, CH2Cl2,
25 °C, 3 h; e) NaBH4, THF/MeOH 4:1 v/v, 0 °C, 3 h. Overall yield from 24 to 28: 56% (2 steps).
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chain as complement linkable functionalities via SN-reaction reduced to oxazolidine 27. Again, similar to 25, cyclization took
was initiated by mesylation. Unfortunately, the mesylated fluo- place and ammonium triflate 28 was isolated in 56% yield
rene showed such a high reactivity that rapid decomposition (starting from 24). In contrast to the cyclization of oxazoline 24,
occurred. However, bromination was conducted by various sub- oxazolidine 27 cyclized already during the reaction, caused by
stitution methods delivering benzyl bromide 24, which upon the increased basicity of the ring nitrogen.
isolation cyclized to iminium bromide 25 in high yield. To
suppress this unexpected cyclization, careful fine-adjustment of CuAAC reactions of bromocarbaldehydes
the work-up conditions were made. Here, upon complete forma- We further investigated the reactivity of azide-functionalized
tion of 24, rapid filtration of the reaction mixture through a plug bromocarbaldehydes 3, 4, and 5 in copper(I)-catalyzed
of neutral alumina, solvent evaporation and quick conversion in azide–alkyne cycloaddition reactions (CuAAC). For this, we
the next step was successfully applied. Deprotection to the treated the azide-functionalized luminophores with alkynes ex-
carbaldehyde was performed using the well applied three-step hibiting different degrees of steric demand, including 1-decyne
methylation/reduction/hydrolysis sequence. Methylation of the (29), phenylacetylene (30), 1-ethynyladamantane (31) and 1,3-
oxazoline nitrogen afforded iminium salt 26, which was di-tert-butyl-5-ethynylbenzene (32, see Scheme 5). All tri-
Scheme 5: a) CuAAC reactions of azide-functionalized bromocarbaldehydes 3, 4 and 5 with terminal alkynes to triazoles 33–44. General reaction
conditions for CuAAC reactions: Azide (1.00 equiv), terminal alkyne (1.05 equiv), CuSO4·5H2O (0.1 equiv), sodium ascorbate (0.50 equiv), CHCl3,
(0.1 M) and water (12.5 mM) at 25 °C for 48 h. b) Methylation reaction of adamantly-substituted triazole 42 with Meerwein′s salt (trimethyloxonium
tetrafluoroborate).
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azoles 33–44, based on the bromocarbaldehydes 3, 4, and 5 These observations for the para- and ortho-bromobenzalde-
were successfully isolated in excellent yields of >90%. As a hydes indicate that the phosphorescence is quenched in these
further model functionalization, the sterically demanding systems, yielding only a weak fluorescence. This may be owing
adamantyl substituted triazole 42 was subjected to a methyla- to the azide moiety, either as a functional group or as part of the
tion reaction with Meerwein′s salt (trimethyloxonium tetra- triazole heterocycle. Similar observations were already made
fluoroborate) to deliver the N-methylated triazole 45 in 83% for luminescent materials [74,75].
yield.
Fluorene derivatives were subjected to photophysical measure-
Photophysical properties
ments as well. UV–vis absorption spectra of bromofluorenecar-
Finally, we examined the photophysical properties of both the baldehydes 5 and 16 show intense absorption bands at 331 and
azides and the triazoles. UV–vis absorption measurements of 330 nm. Furthermore, adamantyltriazole 42 and the correspond-
para-bromobenzaldehyde 3 and ortho-bromobenzaldehyde 4 as ing tetrafluoroborate salt 45 exhibit similar absorption proper-
well as the corresponding triazoles 33–40 were conducted in ties, while the methylated species 45 shows a comparable
chloroform. Intense absorption bands below 270 nm were ob- slightly red-shifted absorption band (see Figure 3a and Figures
served, which could be attributed to typical π–π* transitions S12–S14 in Supporting Information File 1). Emission measure-
derived from the single-benzene core. In addition, unstructured ments of carbaldehydes 5 and 16 revealed that the solid-state
absorption bands above 290 nm were observed, while ortho-de- emission bands are more blue-shifted than the emission bands
rivatives exhibited more broadened bands than the para-deriva- in solution (see Figure 3b). Similar observations were made for
tives (see Figure 2a and Figures S1–S11 in Supporting Informa- adamantyltriazole 42 and tetrafluoroborate salt 45 with maxima
tion File 1). The emission spectra for para-bromocarbaldehyde at 510 nm and 540 nm (see Figure 3c). However, TCSPC
3 and adamantyltriazole 34 in the solid-state show maxima at demonstrated that solely fluorescence was observed in all physi-
440 nm (for compound 3) and 416 nm (for compound 34) (see cal states for all investigated compounds with a maximum life-
Figure 2b). Additionally, fluorescence lifetimes (τ) of 3 and 34 time τ of 11.6 ns for methylated triazole 45 in chloroform (see
were determined by time correlated single photon counting Figure 3d). Quantum yields Φ were determined to be <1% for
(TCSPC), indicating low lifetimes of 2.21 ns (for compound 3) all structures. Further fluorene derivatives – methoxymethyl
and 3.23 ns (for compound 34) for lower populated species (see carbaldehyde 23, iminium bromide 25 and ammonium triflate
Figure S6, Supporting Information File 1). Quantum yields (Φ) 28 – exhibit intense absorption maxima around 320 nm (see
of both derivatives are below 1% in the solid-state. In chloro- Figure S13, Supporting Information File 1). For compounds 25
form, no luminescence was detected for the para derivatives. and 28, the emission maxima in the solid-state were red-shifted
All ortho derivatives exhibited luminescence neither in solution compared to the emission bands in chloroform solution (see
nor in the solid-state [73].
Figures S31 and S33, Supporting Information File 1). Alde-
Figure 2: a) Normalized UV–vis absorption spectra of 3 (blue line), 34 (olive line), 4 (green line) and 38 (red line) in CHCl3 (c = 10−5 mol·L−1).
b) Normalized emission spectra of 3 (navy line), 34 (green line) in the solid-state.
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Figure 3: a) Normalized UV–vis absorption spectra of 5 (blue line), 16 (green line), 42 (olive line) and 45 (red line) in CHCl3. b) Normalized emission
spectra of 5 (in solution, blue line and in the solid-state, green line) and 16 (in solution, olive line and in the solid-state, red line). c) Normalized emis-
sion spectra of 42 (in solution, blue line and in the solid-state, green line) and 45 (in solution, olive line and in the solid-state, red line). d) Time
resolved emission decay curves of 5 (in solution, blue dots and in the solid-state, green dots), 42 (in solution, olive dots) and 45 (in solution, red dots)
at 25 °C. In all diluted measurements (c = 10−5 mol·L−1) CHCl3 was used as solvent and solutions were sparged with argon for 30 minutes.
hyde 23 exhibits a deep violet emission maximum at 360 nm in tions. Efforts of installing other functional groups suitable for
chloroform solution and no emission in the solid-state (see covalent connections or modifications of the alkyl bridge be-
Figure S30, Supporting Information File 1). Lifetimes τ were tween the arene and the azide are underway in our laboratories.
defined up to 8.66 ns for iminium bromide 25, with quantum
yields Φ below 1% (see Figure S32, Supporting Information
File 1). The absence of any long living triplet species in all fluo-
rene derivatives in solution as well as in the solid-state again in-
dicates undesirable quenching events, induced by the azide
functionalities, similar to para- and ortho-bromobenzaldehydes.
Supporting Information
Supporting Information File 1
Detailed experimental procedures, characterization data,
photophysical properties, and copies of NMR spectra.
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-16-139-S1.pdf]
Conclusion
In summary, azide-functionalized ortho- and para-bromobenz-
aldehydes and fluorene derivatives were successfully synthe-
sized. The azide bearing arenes were efficiently linked with
even sterically highly demanding alkynes in CuAAC. Initial Acknowledgements
photophysical investigations of azide-functionalized bromocar- We thank Prof. Dr. Nadja-C. Bigall, Dr. Dirk Dorfs and Pascal
baldehydes and fluorenes revealed that the azide moiety and the Rusch (all from Leibniz University Hannover) for supporting
triazole heterocycle efficiently quench phosphorescent transi- the photophysical measurements.
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22.Lower, S. K.; El-Sayed, M. A. Chem. Rev. 1966, 66, 199–241.
doi:10.1021/cr60240a004
ORCID® iDs
Marius Friedrich - https://orcid.org/0000-0002-7309-5288
23.El‐Sayed, M. A. J. Chem. Phys. 1963, 38, 2834–2838.
doi:10.1063/1.1733610
Enno Lork - https://orcid.org/0000-0002-0582-9913
Boris J. Nachtsheim - https://orcid.org/0000-0002-3759-2770
24.Hirata, S. Adv. Opt. Mater. 2017, 5, 1700116.
doi:10.1002/adom.201700116
25.Menning, S.; Krämer, M.; Coombs, B. A.; Rominger, F.; Beeby, A.;
Dreuw, A.; Bunz, U. H. F. J. Am. Chem. Soc. 2013, 135, 2160–2163.
doi:10.1021/ja400416r
Preprint
A non-peer-reviewed version of this article has been previously published
as a preprint https://doi.org/10.26434/chemrxiv.12238967.v1
26.Yuan, W. Z.; Shen, X. Y.; Zhao, H.; Lam, J. W. Y.; Tang, L.; Lu, P.;
Wang, C.; Liu, Y.; Wang, Z.; Zheng, Q.; Sun, J. Z.; Ma, Y.; Tang, B. Z.
J. Phys. Chem. C 2010, 114, 6090–6099. doi:10.1021/jp909388y
27.Zhang, G.; Chen, J.; Payne, S. J.; Kooi, S. E.; Demas, J. N.;
Fraser, C. L. J. Am. Chem. Soc. 2007, 129, 8942–8943.
doi:10.1021/ja0720255
References
1. Kabe, R.; Notsuka, N.; Yoshida, K.; Adachi, C.
Adv. Mater. (Weinheim, Ger.) 2016, 28, 655–660.
doi:10.1002/adma.201504321
28.Xu, J.; Takai, A.; Kobayashi, Y.; Takeuchi, M. Chem. Commun. 2013,
49, 8447–8449. doi:10.1039/c3cc44809f
2. Tao, Y.; Yang, C.; Qin, J. Chem. Soc. Rev. 2011, 40, 2943–2970.
doi:10.1039/c0cs00160k
29.Schulze, M.; Steffen, A.; Würthner, F. Angew. Chem., Int. Ed. 2015, 54,
1570–1573. doi:10.1002/anie.201410437
3. Goushi, K.; Yoshida, K.; Sato, K.; Adachi, C. Nat. Photonics 2012, 6,
253–258. doi:10.1038/nphoton.2012.31
30.Hirata, S.; Totani, K.; Yamashita, T.; Adachi, C.; Vacha, M. Nat. Mater.
2014, 13, 938–946. doi:10.1038/nmat4081
4. Zhang, Q.; Li, B.; Huang, S.; Nomura, H.; Tanaka, H.; Adachi, C.
Nat. Photonics 2014, 8, 326–332. doi:10.1038/nphoton.2014.12
5. Chaudhuri, D.; Wettach, H.; van Schooten, K. J.; Liu, S.; Sigmund, E.;
Höger, S.; Lupton, J. M. Angew. Chem., Int. Ed. 2010, 49, 7714–7717.
doi:10.1002/anie.201003291
31.Pan, Z.; Lu, Y.-Y.; Liu, F. Nat. Mater. 2012, 11, 58–63.
doi:10.1038/nmat3173
32.Tong, B.; Mei, Q.; Wang, S.; Fang, Y.; Meng, Y.; Wang, B.
J. Mater. Chem. 2008, 18, 1636–1639. doi:10.1039/b800977e
33.Liu, Z. W.; Guan, M.; Bian, Z. Q.; Nie, D. B.; Gong, Z. L.; Li, Z. B.;
Huang, C. H. Adv. Funct. Mater. 2006, 16, 1441–1448.
doi:10.1002/adfm.200600099
6. Chaudhuri, D.; Sigmund, E.; Meyer, A.; Röck, L.; Klemm, P.;
Lautenschlager, S.; Schmid, A.; Yost, S. R.; Van Voorhis, T.;
Bange, S.; Höger, S.; Lupton, J. M. Angew. Chem., Int. Ed. 2013, 52,
13449–13452. doi:10.1002/anie.201307601
34.Zhao, J.; Chen, K.; Hou, Y.; Che, Y.; Liu, L.; Jia, D. Org. Biomol. Chem.
2018, 16, 3692–3701. doi:10.1039/c8ob00421h
7. Murawski, C.; Leo, K.; Gather, M. C. Adv. Mater. (Weinheim, Ger.)
2013, 25, 6801–6827. doi:10.1002/adma.201301603
8. Baldo, M. A.; O'Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.;
Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151–154.
doi:10.1038/25954
35.Forni, A.; Lucenti, E.; Botta, C.; Cariati, E. J. Mater. Chem. C 2018, 6,
4603–4626. doi:10.1039/c8tc01007b
36.Baroncini, M.; Bergamini, G.; Ceroni, P. Chem. Commun. 2017, 53,
2081–2093. doi:10.1039/c6cc09288h
9. Gao, R.; Mei, X.; Yan, D.; Liang, R.; Wei, M. Nat. Commun. 2018, 9,
2798. doi:10.1038/s41467-018-05223-3
37.Mukherjee, S.; Thilagar, P. Chem. Commun. 2015, 51, 10988–11003.
doi:10.1039/c5cc03114a
10.Miao, Q.; Xie, C.; Zhen, X.; Lyu, Y.; Duan, H.; Liu, X.; Jokerst, J. V.;
Pu, K. Nat. Biotechnol. 2017, 35, 1102–1110. doi:10.1038/nbt.3987
11.Zhen, X.; Tao, Y.; An, Z.; Chen, P.; Xu, C.; Chen, R.; Huang, W.; Pu, K.
Adv. Mater. (Weinheim, Ger.) 2017, 29, 1606665.
38.Shi, H.; Song, L.; Ma, H.; Sun, C.; Huang, K.; Lv, A.; Ye, W.; Wang, H.;
Cai, S.; Yao, W.; Zhang, Y.; Zheng, R.; An, Z.; Huang, W.
J. Phys. Chem. Lett. 2019, 10, 595–600.
doi:10.1021/acs.jpclett.8b03712
doi:10.1002/adma.201606665
39.Li, J.-A.; Zhou, J.; Mao, Z.; Xie, Z.; Yang, Z.; Xu, B.; Liu, C.; Chen, X.;
Ren, D.; Pan, H.; Shi, G.; Zhang, Y.; Chi, Z. Angew. Chem., Int. Ed.
2018, 57, 6449–6453. doi:10.1002/anie.201800762
40.Xiong, Y.; Zhao, Z.; Zhao, W.; Ma, H.; Peng, Q.; He, Z.; Zhang, X.;
Chen, Y.; He, X.; Lam, J. W. Y.; Tang, B. Z. Angew. Chem., Int. Ed.
2018, 57, 7997–8001. doi:10.1002/anie.201800834
41.Gu, L.; Shi, H.; Miao, C.; Wu, Q.; Cheng, Z.; Cai, S.; Gu, M.; Ma, C.;
Yao, W.; Gao, Y.; An, Z.; Huang, W. J. Mater. Chem. C 2018, 6,
226–233. doi:10.1039/c7tc04452f
12.Zhang, G.; Palmer, G. M.; Dewhirst, M. W.; Fraser, C. L. Nat. Mater.
2009, 8, 747–751. doi:10.1038/nmat2509
13.DeRosa, C. A.; Seaman, S. A.; Mathew, A. S.; Gorick, C. M.; Fan, Z.;
Demas, J. N.; Peirce, S. M.; Fraser, C. L. ACS Sens. 2016, 1,
1366–1373. doi:10.1021/acssensors.6b00533
14.Lehner, P.; Staudinger, C.; Borisov, S. M.; Klimant, I. Nat. Commun.
2014, 5, 4460. doi:10.1038/ncomms5460
15.Kwon, M. S.; Lee, D.; Seo, S.; Jung, J.; Kim, J. Angew. Chem., Int. Ed.
2014, 53, 11177–11181. doi:10.1002/anie.201404490
16.Xiao, L.; Fu, H. Chem. – Eur. J. 2019, 25, 714–723.
doi:10.1002/chem.201802819
42.Cai, S.; Shi, H.; Zhang, Z.; Wang, X.; Ma, H.; Gan, N.; Wu, Q.;
Cheng, Z.; Ling, K.; Gu, M.; Ma, C.; Gu, L.; An, Z.; Huang, W.
Angew. Chem., Int. Ed. 2018, 57, 4005–4009.
17.Jia, W.; Wang, Q.; Shi, H.; An, Z.; Huang, W. Chem. – Eur. J. 2020, 26,
4437–4448. doi:10.1002/chem.201904500
doi:10.1002/anie.201800697
43.Cai, S.; Shi, H.; Tian, D.; Ma, H.; Cheng, Z.; Wu, Q.; Gu, M.; Huang, L.;
An, Z.; Peng, Q.; Huang, W. Adv. Funct. Mater. 2018, 28, 1705045.
doi:10.1002/adfm.201705045
18.Kasha, M. Chem. Rev. 1947, 41, 401–419. doi:10.1021/cr60129a015
19.Lewis, G. N.; Calvin, M. J. Am. Chem. Soc. 1945, 67, 1232–1233.
doi:10.1021/ja01223a513
44.Cai, S.; Shi, H.; Li, J.; Gu, L.; Ni, Y.; Cheng, Z.; Wang, S.; Xiong, W.-w.;
Li, L.; An, Z.; Huang, W. Adv. Mater. (Weinheim, Ger.) 2017, 29,
1701244. doi:10.1002/adma.201701244
20.Lewis, G. N.; Kasha, M. J. Am. Chem. Soc. 1944, 66, 2100–2116.
doi:10.1021/ja01240a030
21.Lewis, G. N.; Lipkin, D.; Magel, T. T. J. Am. Chem. Soc. 1941, 63,
3005–3018. doi:10.1021/ja01856a043
1691

Beilstein J. Org. Chem. 2020, 16, 1683–1692.
45.Yang, Z.; Mao, Z.; Zhang, X.; Ou, D.; Mu, Y.; Zhang, Y.; Zhao, C.;
Liu, S.; Chi, Z.; Xu, J.; Wu, Y.-C.; Lu, P.-Y.; Lien, A.; Bryce, M. R.
Angew. Chem., Int. Ed. 2016, 55, 2181–2185.
65.Kuila, S.; Rao, K. V.; Garain, S.; Samanta, P. K.; Das, S.; Pati, S. K.;
Eswaramoorthy, M.; George, S. J. Angew. Chem., Int. Ed. 2018, 57,
17115–17119. doi:10.1002/anie.201810823
doi:10.1002/anie.201509224
66.Yu, Z.; Wu, Y.; Xiao, L.; Chen, J.; Liao, Q.; Yao, J.; Fu, H.
J. Am. Chem. Soc. 2017, 139, 6376–6381. doi:10.1021/jacs.7b01574
67.Huang, C.-H.; Wu, P.-J.; Chung, K.-Y.; Chen, Y.-A.; Li, E. Y.;
Chou, P.-T. Phys. Chem. Chem. Phys. 2017, 19, 8896–8901.
doi:10.1039/c7cp00074j
46.Gong, Y.; Chen, G.; Peng, Q.; Yuan, W. Z.; Xie, Y.; Li, S.; Zhang, Y.;
Tang, B. Z. Adv. Mater. (Weinheim, Ger.) 2015, 27, 6195–6201.
doi:10.1002/adma.201502442
47.An, Z.; Zheng, C.; Tao, Y.; Chen, R.; Shi, H.; Chen, T.; Wang, Z.; Li, H.;
Deng, R.; Liu, X.; Huang, W. Nat. Mater. 2015, 14, 685–690.
doi:10.1038/nmat4259
68.Ventura, B.; Bertocco, A.; Braga, D.; Catalano, L.; d’Agostino, S.;
Grepioni, F.; Taddei, P. J. Phys. Chem. C 2014, 118, 18646–18658.
doi:10.1021/jp5049309
48.Yu, Z.; Wu, Y.; Peng, Q.; Sun, C.; Chen, J.; Yao, J.; Fu, H.
Chem. – Eur. J. 2016, 22, 4717–4722. doi:10.1002/chem.201600300
49.Chen, X.; Xu, C.; Wang, T.; Zhou, C.; Du, J.; Wang, Z.; Xu, H.; Xie, T.;
Bi, G.; Jiang, J.; Zhang, X.; Demas, J. N.; Trindle, C. O.; Luo, Y.;
Zhang, G. Angew. Chem., Int. Ed. 2016, 55, 9872–9876.
doi:10.1002/anie.201601252
69.Koch, M.; Perumal, K.; Blacque, O.; Garg, J. A.; Saiganesh, R.;
Kabilan, S.; Balasubramanian, K. K.; Venkatesan, K.
Angew. Chem., Int. Ed. 2014, 53, 6378–6382.
doi:10.1002/anie.201402199
70.Göbel, D.; Clamor, N.; Nachtsheim, B. J. Org. Biomol. Chem. 2018, 16,
4071–4075. doi:10.1039/c8ob01072b
50.Lin, Z.; Kabe, R.; Nishimura, N.; Jinnai, K.; Adachi, C.
Adv. Mater. (Weinheim, Ger.) 2018, 30, 1803713.
doi:10.1002/adma.201803713
71.Göbel, D.; Clamor, N.; Lork, E.; Nachtsheim, B. J. Org. Lett. 2019, 21,
5373–5377. doi:10.1021/acs.orglett.9b01350
51.Li, D.; Lu, F.; Wang, J.; Hu, W.; Cao, X.-M.; Ma, X.; Tian, H.
J. Am. Chem. Soc. 2018, 140, 1916–1923. doi:10.1021/jacs.7b12800
52.Kabe, R.; Adachi, C. Nature 2017, 550, 384–387.
doi:10.1038/nature24010
72.Göbel, D.; Duvinage, D.; Stauch, T.; Nachtsheim, B. J.
J. Mater. Chem. C 2020. doi:10.1039/d0tc00776e
73.Sarkar, S.; Hendrickson, H. P.; Lee, D.; DeVine, F.; Jung, J.; Geva, E.;
Kim, J.; Dunietz, B. D. J. Phys. Chem. C 2017, 121, 3771–3777.
doi:10.1021/acs.jpcc.6b12027
53.Gan, N.; Wang, X.; Ma, H.; Lv, A.; Wang, H.; Wang, Q.; Gu, M.; Cai, S.;
Zhang, Y.; Fu, L.; Zhang, M.; Dong, C.; Yao, W.; Shi, H.; An, Z.;
Huang, W. Angew. Chem., Int. Ed. 2019, 58, 14140–14145.
doi:10.1002/anie.201907572
74.Xie, S.; Proietti, G.; Ramström, O.; Yan, M. J. Org. Chem. 2019, 84,
14520–14528. doi:10.1021/acs.joc.9b02050
75.Lord, S. J.; Lee, H.-l. D.; Samuel, R.; Weber, R.; Liu, N.; Conley, N. R.;
Thompson, M. A.; Twieg, R. J.; Moerner, W. E. J. Phys. Chem. B 2010,
114, 14157–14167. doi:10.1021/jp907080r
54.Yang, J.; Ren, Z.; Chen, B.; Fang, M.; Zhao, Z.; Tang, B. Z.; Peng, Q.;
Li, Z. J. Mater. Chem. C 2017, 5, 9242–9246. doi:10.1039/c7tc03656f
55.Shimizu, M.; Shigitani, R.; Nakatani, M.; Kuwabara, K.; Miyake, Y.;
Tajima, K.; Sakai, H.; Hasobe, T. J. Phys. Chem. C 2016, 120,
11631–11639. doi:10.1021/acs.jpcc.6b03276
License and Terms
56.Xie, Y.; Ge, Y.; Peng, Q.; Li, C.; Li, Q.; Li, Z.
Adv. Mater. (Weinheim, Ger.) 2017, 29, 1606829.
doi:10.1002/adma.201606829
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57.Bergamini, G.; Fermi, A.; Botta, C.; Giovanella, U.; Di Motta, S.;
Negri, F.; Peresutti, R.; Gingras, M.; Ceroni, P. J. Mater. Chem. C
2013, 1, 2717–2724. doi:10.1039/c3tc00878a
(http://creativecommons.org/licenses/by/4.0). Please note
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58.Bolton, O.; Lee, K.; Kim, H.-J.; Lin, K. Y.; Kim, J. Nat. Chem. 2011, 3,
205–210. doi:10.1038/nchem.984
59.Yu, Y.; Kwon, M. S.; Jung, J.; Zeng, Y.; Kim, M.; Chung, K.;
Gierschner, J.; Youk, J. H.; Borisov, S. M.; Kim, J.
Angew. Chem., Int. Ed. 2017, 56, 16207–16211.
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60.Kwon, M. S.; Jordahl, J. H.; Phillips, A. W.; Chung, K.; Lee, S.;
Gierschner, J.; Lahann, J.; Kim, J. Chem. Sci. 2016, 7, 2359–2363.
doi:10.1039/c5sc03986j
The definitive version of this article is the electronic one
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61.Kwon, M. S.; Yu, Y.; Coburn, C.; Phillips, A. W.; Chung, K.;
Shanker, A.; Jung, J.; Kim, G.; Pipe, K.; Forrest, S. R.; Youk, J. H.;
Gierschner, J.; Kim, J. Nat. Commun. 2015, 6, 8947.
doi:10.1038/ncomms9947
doi:10.3762/bjoc.16.139
62.Lee, D.; Jung, J.; Bilby, D.; Kwon, M. S.; Yun, J.; Kim, J.
ACS Appl. Mater. Interfaces 2015, 7, 2993–2997.
doi:10.1021/am5087165
63.Bolton, O.; Lee, D.; Jung, J.; Kim, J. Chem. Mater. 2014, 26,
6644–6649. doi:10.1021/cm503678r
64.Goudappagouda; Manthanath, A.; Wakchaure, V. C.; Ranjeesh, K. C.;
Das, T.; Vanka, K.; Nakanishi, T.; Babu, S. S. Angew. Chem., Int. Ed.
2019, 58, 2284–2288. doi:10.1002/anie.201811834
1692