Radical-Enhanced Intersystem Crossing in New Bodipy Derivatives and Application for Efficient Triplet–Triplet Annihilation Upconversion

Recently,t he potentialu se of organic p-radicals and relateds pin systems has been expanded to modern technological applications. The unique excited-state dynamics of organic p-radicals can be useful to improvet he stability of photochemically unstable organic compounds, make the polarization transfer applicable to information technology,a nd achieve effective up-conversion of interest for luminescence bioimaging, amongo thers. Furthermore, highly luminescent stable p-radicalsh ave been recently reported, which are especially interesting fora pplication in organic light-emitting devices owing to their potentialt op rovide an internal quantum efficiency of 100 %. Thus,t he excited-state nature of stable p-radicalsa sw ell as the control of their excited-state spin dynamics are emerging topics both in terms of fundamental science and related technological applications. In this minireview,w ef ocus on the excited-state dynamics of both photostable non(weakly)-luminescent and luminescent p-radicals, which are opposites of each other.I n particular, we cover the following topics:1 )effective generation of high-spin photoexcited states and control of the excited-state dynamics by using non-luminescent p-radicals, 2) unique excited-state dynamics of luminescent p-radicals and radical excimers, and 3) applicationsu tilizing excitedstate dynamics of p-radicals.[a] Prof.

“…The radical‐induced EISC was utilized to produce an efficient triplet–triplet annihilation (TTA) photon up‐conversion . Yaglioglu et al.…”

Section: Applications Using Excited‐state Dynamics Of π‐Radicalsmentioning

confidence: 99%

Excited‐State Dynamics of Non‐Luminescent and Luminescent π‐Radicals

Teki

2019

“…As an alternative strategy, singlet fission is attractive as one excited singlet can produce two triplet states, with a maximal triplet quantum yield of 200 %, but the triplet state energy level obtained with this method, especially with visible light‐harvesting chromophores, is low and it is unfavourable for further application based on intermolecular triplet energy transfer or electron transfer. Radical enhanced intersystem crossing (REISC) was also used to prepare heavy atom‐free triplet PSs, but the relationship between the molecular structure (electron spin–spin exchange interaction) and the ISC efficiency is not clear, hence it is difficult to predict the ISC efficiency of systems relying on this mechanism …”

Section: Introductionmentioning

confidence: 99%

Spin–Orbit Charge‐Transfer Intersystem Crossing (ISC) in Compact Electron Donor–Acceptor Dyads: ISC Mechanism and Application as Novel and Potent Photodynamic Therapy Reagents

Wang

Ivanov

Gao

et al. 2020

Self Cite

104

Spin-orbit charge-transfer intersystem crossing (SOCT-ISC) is useful for the preparation of heavy atom-free triplet photosensitisers( PSs). Herein, as eries of perylene-Bodipy compact electrond onor/acceptor dyads showing efficient SOCT-ISC is prepared. The photophysical properties of the dyads were studiedw ith steady-state and time-resolved spectroscopies. Efficient triplet state formation (quantum yield F T = 60 %) waso bserved, with at riplets tate lifetime (t T = 436 ms) much longert han that accessed with the conventional heavy atom effect (t T = 62 ms). The SOCT-ISC mechanism wasu nambiguously confirmed by direct excitation of the charget ransfer (CT) absorption band by using nanosecond transienta bsorption spectroscopy and time-resolved electronp aramagnetic resonance (TREPR) spectroscopy.T he factors affecting the SOCT-ISC efficiency include the geometry,t he potential energy surfaceo ft he torsion, the spin density for the atoms of the linker,s olvent polarity,a nd the energym atchingo ft he 1 CT/ 3 LE states. Remarkably,t hese heavya tom-free triplet PSs were demonstrated as an ew type of efficient photodynamic therapy (PDT) reagents (phototoxicity,E C 50 = 75 nm), with an egligibled ark toxicity (EC 50 = 78.1 mm)c ompared with the conventionalh eavy atom PSs (dark toxicity,E C 50 = 6.0 mm, light toxicity, EC 50 = 4.0 nm). This study provides in-depthu nderstanding of the SOCT-ISC, unveils the design principles of triplet PSs based on SOCT-ISC, andu nderlines their applicationa sanew generationo fp otent PDT reagents.[a] Dr.[h] Prof. M. Di Donato INO, Istituto Nazionale di Ottica Largo Enrico Fermi 6, 50125F lorence (Italy)[ + + ] These authorscontributed equally to this work.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

“…The use of radicals to enhance ISC is of particular interest, and is often referred to as radical‐enhanced ISC (REISC) . The REISC mechanism is based on the spin–spin exchange of the electrons localized on the radical and on the electronically excited chromophore.…”

Section: Introductionmentioning

confidence: 99%

“…With spin–spin interactions between the radical and the electronically excited chromophore, the three‐spin system may form a doublet state (D, total spin quantum number S =1/2) or a quartet state (Q, total spin quantum number S =3/2). The formation of the doublet spin state is beneficial for ISC: the ISC of the chromophore is within the overall D n →D 1 transition of the dyad, which is a spin‐allowed process (herein for the D n state, the chromophore is in the singlet state; for the D 1 state, the chromophore is in the triplet state) . Previously, radical‐labeled fluorophores have mainly been used as fluorescent molecular probes for the selective detection of reactive radicals, based on the quenching of fluorescence by the attached radical on the fluorophore, and fluorescence recovery of the fluorophore upon reaction of the radical with the analytes.…”

Section: Introductionmentioning

confidence: 99%

“…The electron spin dynamics of these molecular systems were characterized with time‐resolved electron paramagnetic resonance (TREPR) spectroscopy . However, little attention has been devoted to characterizing the chromophore localized triplet formation in these systems in terms of triplet photosensitizers . Moreover, only a limited number of chromophores have been used in REISC, for instance, naphthalene, anthracene, perylene, pyrene, perylenebisimide, and bodipy .…”

Section: Introductionmentioning

confidence: 99%

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Intersystem Crossing in Naphthalenediimide–Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

Hussain

Taddei²,

Bussotti³

et al. 2019

Self Cite

Oxoverdazyl( Vz) radicalu nits were covalently linked to the naphthalenediimide (NDI) chromophore to study the effect of the radicalo nt he photophysical properties, especially the radicale nhanced intersystem crossing (REISC), which is ap romisinga pproach to develop heavyatom-free triplet photosensitizers. Rigid phenylo re thynylphenyll inkers betweent he two moieties were used, thus REISC andf ormation of doublet (D 1 ,t otal spin quantum number S = 1/2) and quartet states (Q 1 , S = 3/2) are anticipated. The photophysical properties of the dyadsw ere studied with steady-statea nd femtosecond/nanosecond transient absorption (TA) spectroscopiesa nd DFT computations. Femtosecond transienta bsorption spectras how af ast electron transfer (< 150 fs), and ISC (ca. 1.4-1.85ps) is induced by charger ecombination (CR, in toluene). Nanosecond transient absorption spectra demonstrated ab iexponential decay of the triplet state of the NDI moiety.T he fast component (lifetime:5 0ns; population ratio:8 0%)i sa ssigned to the D 1 ! D 0 decay,a nd the slow decay component (2.0 ms; 20 %) to the Q 1 !D 0 ISC. DFT computations indicated ferromagnetic interactions between the radicala nd chromophore( J = 0.07-0.13 eV). Reversible formation of the radical aniono ft he NDI moiety by photoreduction of the radical-NDI dyadsi nt he presence of sacrificial electron donor triethanolamine (TEOA) is achieved. This work is useful for design of new triplet photosensitizers based on the REISC effect.