Radical enhanced intersystem crossing (EISC) of organic chromophores is an important approach to generate a long-lived triplet state for various electronic and optoelectronic applications. However, structural factors and design rules to promote EISC are not entirely clear. In this work, we report a series of boron dipyrromethene (BODIPY) derivatives covalently linked with a 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical with varying distances and topologies. We show that the incorporation of the TEMPO radical to BODIPY results in strong fluorescence quenching by up to 85% as a result of EISC and enhanced internal conversion. In BDP-2AR [2-(4-methyleneamino-TEMPO) BODIPY], a dyad with the shortest BODIPY–TEMPO through-bond distance, we observe the fastest EISC rate (τisc = 1.4 ns) and the longest triplet excited state lifetime (τT = 32 µs) compared to other distance and geometry variations. Contrary to previous reports and a general presumption, the BODIPY–TEMPO through-bond distance in this system does not play a significant role on the triplet formation rate and yield. Density functional theory suggests a folding of the TEMPO radical to form a sandwich-like structure with a BODIPY ring that leads to a decrease in the through-space distance, providing a new and an interesting insight for the radical enhanced intersystem.
REFERENCES
1.
C. K.
Prier
, D. A.
Rankic
, and D. W. C.
MacMillan
, “Visible light photoredox catalysis with transition metal complexes: Applications in organic synthesis
,” Chem. Rev.
113
(7
), 5322
–5363
(2013
).2.
Y.
Cakmak
, S.
Kolemen
, S.
Duman
, Y.
Dede
, Y.
Dolen
, B.
Kilic
, Z.
Kostereli
, L. T.
Yildirim
, A. L.
Dogan
, D.
Guc
, and E. U.
Akkaya
, “Designing excited states: Theory-guided access to efficient photosensitizers for photodynamic action
,” Angew. Chem., Int. Ed.
50
(50
), 11937
–11941
(2011
).3.
A.
Kamkaew
, S. H.
Lim
, H. B.
Lee
, L. V.
Kiew
, L. Y.
Chung
, and K.
Burgess
, “BODIPY dyes in photodynamic therapy
,” Chem. Soc. Rev.
42
(1
), 77
–88
(2013
).4.
S. H.
Lim
, C.
Thivierge
, P.
Nowak-Sliwinska
, J.
Han
, H.
van den Bergh
, G.
Wagnières
, K.
Burgess
, and H. B.
Lee
, “In vitro and in vivo photocytotoxicity of boron dipyrromethene derivatives for photodynamic therapy
,” J. Med. Chem.
53
(7
), 2865
–2874
(2010
).5.
J.
Zhao
, K.
Xu
, W.
Yang
, Z.
Wang
, and F.
Zhong
, “The triplet excited state of Bodipy: Formation, modulation and application
,” Chem. Soc. Rev.
44
(24
), 8904
–8939
(2015
).6.
A.
Rao
, P. C. Y.
Chow
, S.
Gélinas
, C. W.
Schlenker
, C.-Z.
Li
, H.-L.
Yip
, A. K.-Y.
Jen
, D. S.
Ginger
, and R. H.
Friend
, “The role of spin in the kinetic control of recombination in organic photovoltaics
,” Nature
500
(7463
), 435
–439
(2013
).7.
W.
Wu
, H.
Guo
, W.
Wu
, S.
Ji
, and J.
Zhao
, “Organic triplet sensitizer library derived from a single chromophore (BODIPY) with long-lived triplet excited state for triplet–triplet annihilation based upconversion
,” J. Org. Chem.
76
(17
), 7056
–7064
(2011
).8.
J.
Zhao
, S.
Ji
, and H.
Guo
, “Triplet–triplet annihilation based upconversion: From triplet sensitizers and triplet acceptors to upconversion quantum yields
,” RSC Adv.
1
(6
), 937
–950
(2011
).9.
Z.
Wang
, J.
Zhao
, A.
Barbon
, A.
Toffoletti
, Y.
Liu
, Y.
An
, L.
Xu
, A.
Karatay
, H. G.
Yaglioglu
, E. A.
Yildiz
, and M.
Hayvali
, “Radical-enhanced intersystem crossing in new Bodipy derivatives and application for efficient triplet–triplet annihilation upconversion
,” J. Am. Chem. Soc.
139
(23
), 7831
–7842
(2017
).10.
K.
Xu
, A. A.
Sukhanov
, Y.
Zhao
, J.
Zhao
, W.
Ji
, X.
Peng
, D.
Escudero
, D.
Jacquemin
, and V. K.
Voronkova
, “Unexpected nucleophilic substitution reaction of BODIPY: Preparation of the BODIPY–TEMPO triad showing radical-enhanced intersystem crossing
,” Eur. J. Org. Chem.
2018
(7
), 885
–895
.11.
T. N.
Singh-Rachford
and F. N.
Castellano
, “Photon upconversion based on sensitized triplet–triplet annihilation
,” Coord. Chem. Rev.
254
(21-22
), 2560
–2573
(2010
).12.
J.
Zhou
, Q.
Liu
, W.
Feng
, Y.
Sun
, and F.
Li
, “Upconversion luminescent materials: Advances and applications
,” Chem. Rev.
115
(1
), 395
–465
(2015
).13.
H.
Yersin
, A. F.
Rausch
, R.
Czerwieniec
, T.
Hofbeck
, and T.
Fischer
, “The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs
,” Coord. Chem. Rev.
255
(21-22
), 2622
–2652
(2011
).14.
N. A.
Romero
and D. A.
Nicewicz
, “Organic photoredox catalysis
,” Chem. Rev.
116
(17
), 10075
–10166
(2016
).15.
C. J.
Bardeen
, “The structure and dynamics of molecular excitons
,” Annu. Rev. Phys. Chem.
65
(1
), 127
–148
(2014
).16.
T. W.
Schmidt
and F. N.
Castellano
, “Photochemical upconversion: The primacy of kinetics
,” J. Phys. Chem. Lett.
5
(22
), 4062
–4072
(2014
).17.
W.
Shockley
and H. J.
Queisser
, “Detailed balance limit of efficiency of p-n junction solar cells
,” J. Appl. Phys.
32
(3
), 510
–519
(1961
).18.
J.
de Wild
, A.
Meijerink
, J. K.
Rath
, W. G. J. H. M.
van Sark
, R. E. I.
Schropp
, G.
Nelles
, A.
Yasuda
, S.
Chernov
, S.
Aleshchenkov
, A.
Cheprakov
, A.
Manthiram
, A.
Nozik
, D. R.
Rolison
, T.
Sands
, L.
Shi
, D.
Sholl
, and Y.
Wu
, “Upconverter solar cells: Materials and applications
,” Energy Environ. Sci.
4
(12
), 4835
–4848
(2011
).19.
T. N.
Singh-Rachford
, A.
Haefele
, R.
Ziessel
, and F. N.
Castellano
, “Boron dipyrromethene chromophores: Next generation triplet acceptors/annihilators for low power upconversion schemes
,” J. Am. Chem. Soc.
130
(48
), 16164
–16165
(2008
).20.
J.
Zhao
, W.
Wu
, J.
Sun
, and S.
Guo
, “Triplet photosensitizers: From molecular design to applications
,” Chem. Soc. Rev.
42
(12
), 5323
–5351
(2013
).21.
T.
Jin
, N.
Uhlikova
, Z.
Xu
, Y.
Zhu
, Y.
Huang
, E.
Egap
, and T.
Lian
, “Enhanced triplet state generation through radical pair intermediates in BODIPY-quantum dot complexes
,” J. Chem. Phys.
151
(24
), 241101
(2019
).22.
S.
Garakyaraghi
, C.
Mongin
, D. B.
Granger
, J. E.
Anthony
, and F. N.
Castellano
, “Delayed molecular triplet generation from energized lead sulfide quantum dots
,” J. Phys. Chem. Lett.
8
(7
), 1458
–1463
(2017
).23.
J. A.
Bender
, E. K.
Raulerson
, X.
Li
, T.
Goldzak
, P.
Xia
, T.
Van Voorhis
, M. L.
Tang
, and S. T.
Roberts
, “Surface states mediate triplet energy transfer in nanocrystal–acene composite systems
,” J. Am. Chem. Soc.
140
(24
), 7543
–7553
(2018
).24.
N. J.
Turro
, G. J.
Kavarnos
, T.
Cole
, P.
Scribe
, and J. C.
Dalton
, “Molecular photochemistry. XXXIX. External heavy-atom-induced spin-obital coupling. Spectroscopic study of naphthonorbornanes
,” J. Am. Chem. Soc.
93
(4
), 1032
–1034
(1971
).25.
J. C.
Koziar
and D. O.
Cowan
, “Photochemical heavy-atom effects
,” Acc. Chem. Res.
11
(9
), 334
–341
(1978
).26.
E. I.
Carrera
and D. S.
Seferos
, “Semiconducting polymers containing tellurium: Perspectives toward obtaining high-performance materials
,” Macromolecules
48
(2
), 297
–308
(2015
).27.
G. D.
Gutierrez
, G. T.
Sazama
, T.
Wu
, M. A.
Baldo
, and T. M.
Swager
, “Red phosphorescence from benzo[2,1,3]thiadiazoles at room temperature
,” J. Org. Chem.
81
(11
), 4789
–4796
(2016
).28.
Y. P.
Rey
, D. G.
Abradelo
, N.
Santschi
, C. A.
Strassert
, and R.
Gilmour
, “Quantitative profiling of the heavy-atom effect in BODIPY dyes: Correlating initial rates, atomic numbers, and 1O2 quantum yields
,” Eur. J. Org. Chem.
2017
(15
), 2170
–2178
.29.
M. B.
Smith
and J.
Michl
, “Singlet fission
,” Chem. Rev.
110
(11
), 6891
–6936
(2010
).30.
L.
Franco
, M.
Mazzoni
, C.
Corvaja
, V. P.
Gubskaya
, L. S.
Berezhnaya
, and I. A.
Nuretdinov
, “First observation of the hyperfine structure of an excited quintet state in liquid solution
,” Chem. Commun.
33
(16
), 2128
–2130
(2005
).31.
K.
Ishii
, Y.
Hirose
, and N.
Kobayashi
, “Selective population from the excited multiplet states to the triplet ground state in a phthalocyanine: A new concept for controlling magnetic properties by photoexcitation
,” J. Am. Chem. Soc.
120
(40
), 10551
–10552
(1998
).32.
K.
Ishii
, J.-i.
Fujisawa
, A.
Adachi
, S.
Yamauchi
, and N.
Kobayashi
, “General simulations of excited quartet spectra with electron-spin polarizations: The excited multiplet states of (tetraphenylporphinato)zinc(II) coordinated by p- or m-pyridyl nitronyl nitroxides
,” J. Am. Chem. Soc.
120
(13
), 3152
–3158
(1998
).33.
S.
Takeuchi
, K.
Ishii
, and N.
Kobayashi
, “Time-resolved EPR and transient absorption studies on phthalocyaninatosilicon covalently linked to two PROXYL radicals
,” J. Phys. Chem. A
108
(16
), 3276
–3280
(2004
).34.
E. M.
Giacobbe
, Q.
Mi
, M. T.
Colvin
, B.
Cohen
, C.
Ramanan
, A. M.
Scott
, S.
Yeganeh
, T. J.
Marks
, M. A.
Ratner
, and M. R.
Wasielewski
, “Ultrafast intersystem crossing and spin dynamics of photoexcited perylene-3,4:9,10-bis(dicarboximide) covalently linked to a nitroxide radical at fixed distances
,” J. Am. Chem. Soc.
131
(10
), 3700
–3712
(2009
).35.
M. T.
Colvin
, E. M.
Giacobbe
, B.
Cohen
, T.
Miura
, A. M.
Scott
, and M. R.
Wasielewski
, “Competitive electron transfer and enhanced intersystem crossing in photoexcited covalent TEMPO–perylene-3,4:9,10-bis(dicarboximide) dyads: Unusual spin polarization resulting from the radical–triplet interaction
,” J. Phys. Chem. A
114
(4
), 1741
–1748
(2010
).36.
A.
Ito
, A.
Shimizu
, N.
Kishida
, Y.
Kawanaka
, D.
Kosumi
, H.
Hashimoto
, and Y.
Teki
, “Excited-state dynamics of pentacene derivatives with stable radical substituents
,” Angew. Chem., Int. Ed.
53
(26
), 6715
–6719
(2014
).37.
G. I.
Likhtenstein
, K.
Ishii
, and S. i.
Nakatsuji
, “Dual chromophore-nitroxides: Novel molecular probes, photochemical and photophysical models and magnetic materials
,” Photochem. Photobiol.
83
(4
), 871
–881
(2007
).38.
Y.
Huang
and E.
Egap
, “Open-shell organic semiconductors: An emerging class of materials with novel properties
,” Polym. J.
50
, 603
–614
(2018
).39.
A.
Loudet
and K.
Burgess
, “BODIPY dyes and their derivatives: Syntheses and spectroscopic properties
,” Chem. Rev.
107
(11
), 4891
–4932
(2007
).40.
G.
Ulrich
, R.
Ziessel
, and A.
Harriman
, “The chemistry of fluorescent Bodipy dyes: Versatility unsurpassed
,” Angew. Chem., Int. Ed.
47
(7
), 1184
–1201
(2008
).41.
H.
Lu
, J.
Mack
, Y.
Yang
, and Z.
Shen
, “Structural modification strategies for the rational design of red/NIR region BODIPYs
,” Chem. Soc. Rev.
43
(13
), 4778
–4823
(2014
).42.
E.
Ahmed
, S. W.
Morton
, P. T.
Hammond
, and T. M.
Swager
, “Fluorescent multiblock π–conjugated polymer nanoparticles for in vivo tumor targeting
,” Adv. Mater.
25
(32
), 4504
–4510
(2013
).43.
J.
Zhang
, Y.
Huang
, D.
Wang
, A. C.
Pollard
, Z.
Chen
, and E.
Egap
, “Triblock near-infrared fluorescent polymer semiconductor nanoparticles for targeted imaging
,” J. Mater. Chem. C
5
(23
), 5685
–5692
(2017
).44.
Y.
Gabe
, Y.
Urano
, K.
Kikuchi
, H.
Kojima
, and T.
Nagano
, “Highly sensitive fluorescence probes for nitric oxide based on boron dipyrromethene chromophore-rational design of potentially useful bioimaging fluorescence probe
,” J. Am. Chem. Soc.
126
(10
), 3357
–3367
(2004
).45.
T.
Cheng
, J.
Zhao
, Z.
Wang
, J.
An
, Y.
Xu
, X.
Qian
, and G.
Liu
, “A highly sensitive and selective hypochlorite fluorescent probe based on oxidation of hydrazine via free radical mechanism
,” Dyes Pigm.
126
, 218
–223
(2016
).46.
J. P.
Allen
, M. C.
Pfrunder
, J. C.
McMurtrie
, S. E.
Bottle
, J. P.
Blinco
, and K. E.
Fairfull-Smith
, “BODIPY-based profluorescent probes containing meso- and β-substituted isoindoline nitroxides
,” Eur. J. Org. Chem.
2017
(3
), 476
–483
.47.
N. B.
Yapici
, S.
Jockusch
, A.
Moscatelli
, S. R.
Mandalapu
, Y.
Itagaki
, D. K.
Bates
, S.
Wiseman
, K. M.
Gibson
, N. J.
Turro
, and L.
Bi
, “New rhodamine nitroxide based fluorescent probes for intracellular hydroxyl radical identification in living cells
,” Org. Lett.
14
(1
), 50
–53
(2012
).48.
P.
Li
, T.
Xie
, X.
Duan
, F.
Yu
, X.
Wang
, and B.
Tang
, “A new highly selective and sensitive assay for fluorescence imaging of OH in living cells: Effectively avoiding the interference of peroxynitrite
,” Chem. - Eur. J.
16
(6
), 1834
–1840
(2010
).49.
J. C.
Morris
, J. C.
McMurtrie
, S. E.
Bottle
, and K. E.
Fairfull-Smith
, “Generation of profluorescent isoindoline nitroxides using click chemistry
,” J. Org. Chem.
76
(12
), 4964
–4972
(2011
).50.
S. A.
Green
, D. J.
Simpson
, G.
Zhou
, P. S.
Ho
, and N. V.
Blough
, “Intramolecular quenching of excited singlet states by stable nitroxyl radicals
,” J. Am. Chem. Soc.
112
(20
), 7337
–7346
(1990
).51.
S. E.
Herbelin
and N. V.
Blough
, “Intramolecular quenching of excited singlet states in a series of fluorescamine-derivatized nitroxides
,” J. Phys. Chem. B
102
(42
), 8170
–8176
(1998
).52.
Y.
Teki
, S.
Miyamoto
, M.
Nakatsuji
, and Y.
Miura
, “π-topology and spin alignment utilizing the excited molecular field: Observation of the excited high-spin quartet (S = 3/2) and quintet (S = 2) states on purely organic π-conjugated spin systems
,” J. Am. Chem. Soc.
123
(2
), 294
–305
(2001
).53.
C.
Corvaja
, M.
Maggini
, M.
Prato
, G.
Scorrano
, and M.
Venzin
, “C60 derivative covalently linked to a nitroxide radical: Time-resolved EPR evidence of electron spin polarization by intramolecular radical-triplet pair interaction
,” J. Am. Chem. Soc.
117
(34
), 8857
–8858
(1995
).54.
Y.
Miura
, Y.
Ushitani
, K.
Inui
, Y.
Teki
, T.
Takui
, and K.
Itoh
, “Syntheses and magnetic characterization of poly(1,3-phenyleneethynylene) with pendant nitronyl nitroxide radicals
,” Macromolecules
26
(14
), 3698
–3701
(1993
).55.
H.
Nishide
, T.
Kaneko
, T.
Nii
, K.
Katoh
, E.
Tsuchida
, and K.
Yamaguchi
, “Through-bond and long-range ferromagnetic spin alignment in a π-conjugated polyradical with a poly(phenylenevinylene) skeleton
,” J. Am. Chem. Soc.
117
(1
), 548
–549
(1995
).56.
E. T.
Chernick
, R.
Casillas
, J.
Zirzlmeier
, D. M.
Gardner
, M.
Gruber
, H.
Kropp
, K.
Meyer
, M. R.
Wasielewski
, D. M.
Guldi
, and R. R.
Tykwinski
, “Pentacene appended to a TEMPO stable free radical: The effect of magnetic exchange coupling on photoexcited pentacene
,” J. Am. Chem. Soc.
137
(2
), 857
–863
(2015
).57.
J.
Kang
, F.
Huo
, Y.
Yue
, Y.
Wen
, J.
Chao
, Y.
Zhang
, and C.
Yin
, “A solvent depend on ratiometric fluorescent probe for hypochlorous acid and its application in living cells
,” Dyes Pigm.
136
, 852
–858
(2017
).58.
J. H.
Boyer
, A. M.
Haag
, G.
Sathyamoorthi
, M.-L.
Soong
, K.
Thangaraj
, and T. G.
Pavlopoulos
, “Pyrromethene–BF2 complexes as laser dyes: 2
,” Heteroat. Chem.
4
(1
), 39
–49
(1993
).59.
J. A.
Green
, L. A.
Singer
, and J. H.
Parks
, “Fluorescence quenching by the stable free radical di-t-butylnitroxide
,” J. Chem. Phys.
58
(7
), 2690
–2695
(1973
).60.
S. K.
Chattopadhyay
, P. K.
Das
, and G. L.
Hug
, “Photoprocesses in diphenylpolyenes. 2. Excited-state interactions with stable free radicals
,” J. Am. Chem. Soc.
105
(20
), 6205
–6210
(1983
).61.
A.
Weller
, “Photoinduced electron transfer in solution: Exciplex and radical ion pair formation free enthalpies and their solvent dependence
,” Z. Phys. Chem.
133
(1
), 93
–98
(1982
).62.
Z.
Wang
and J.
Zhao
, “Bodipy–anthracene dyads as triplet photosensitizers: Effect of chromophore orientation on triplet-state formation efficiency and application in triplet–triplet annihilation upconversion
,” Org. Lett.
19
(17
), 4492
–4495
(2017
).63.
J.
Al Anshori
, T.
Slanina
, E.
Palao
, and P.
Klán
, “The internal heavy-atom effect on 3-phenylselanyl and 3-phenyltellanyl BODIPY derivatives studied by transient absorption spectroscopy
,” Photochem. Photobiol. Sci.
15
(2
), 250
–259
(2016
).64.
S.
Ji
, J.
Ge
, D.
Escudero
, Z.
Wang
, J.
Zhao
, and D.
Jacquemin
, “Molecular structure–intersystem crossing relationship of heavy-atom-free BODIPY triplet photosensitizers
,” J. Org. Chem.
80
(11
), 5958
–5963
(2015
).65.
Z.
Xu
, T.
Jin
, Y.
Huang
, K.
Mulla
, F. A.
Evangelista
, E.
Egap
, and T.
Lian
, “Direct triplet sensitization of oligothiophene by quantum dots
,” Chem. Sci.
10
(24
), 6120
–6124
(2019
).66.
N.
Adarsh
, R. R.
Avirah
, and D.
Ramaiah
, “Tuning photosensitized singlet oxygen generation efficiency of novel aza–BODIPY dyes
,” Org. Lett.
12
(24
), 5720
–5723
(2010
).67.
M. A.
Filatov
, S.
Karuthedath
, P. M.
Polestshuk
, H.
Savoie
, K. J.
Flanagan
, C.
Sy
, E.
Sitte
, M.
Telitchko
, F.
Laquai
, R. W.
Boyle
, and M. O.
Senge
, “Generation of triplet excited states via photoinduced electron transfer in meso-anthra-BODIPY: Fluorogenic response toward singlet oxygen in solution and in vitro
,” J. Am. Chem. Soc.
139
(18
), 6282
–6285
(2017
).68.
J.-D.
Chai
and M.
Head-Gordon
, “Long-range corrected hybrid density functionals with damped atom–atom dispersion corrections
,” Phys. Chem. Chem. Phys.
10
(44
), 6615
–6620
(2008
).69.
M. M.
Francl
, W. J.
Pietro
, W. J.
Hehre
, J. S.
Binkley
, M. S.
Gordon
, D. J.
DeFrees
, and J. A.
Pople
, “Self-consistent molecular orbital methods. XXIII. A polarization-type basis set for second-row elements
,” J. Chem. Phys.
77
(7
), 3654
–3665
(1982
).70.
F.
Furche
and R.
Ahlrichs
, “Adiabatic time-dependent density functional methods for excited state properties
,” J. Chem. Phys.
117
(16
), 7433
–7447
(2002
).© 2020 Author(s).
2020
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