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

Hussain, Mushraf; Taddei, Maria Letizia; Bussotti, Laura; Foggi, Paolo; Zhao, Jianzhang; Liu, Qingyun; Donato, Mariangela Di

doi:10.1002/chem.201903814

Cited by 13 publications

(21 citation statements)

References 59 publications

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“…However, both D 1 and Q states are with the PBI moiety in the triplet state, therefore, the D 1 and the Q states are indistinguishable in optical transient absorption spectra [47] . We didn't observe biexponential decay of the triplet state, which is different from the recently reported NDI‐verdazyl radical dyads [82] …”

Section: Resultscontrasting

confidence: 98%

“…Interestingly, PBI−NH shows a triplet state lifetime of 15.0 μ s (intermolecular photosensitizing method, see Figures S21 in Supporting Information). These results infer that there is an electron spin‐spin exchange interaction between the radical and the PBI moiety in PBI−TEMPO , by which the triplet state of the PBI may be shortened [56,82] …”

Section: Resultsmentioning

confidence: 87%

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Radical‐Enhanced Intersystem Crossing in a Bay‐Substituted Perylene Bisimide−TEMPO Dyad and the Electron Spin Polarization Dynamics upon Photoexcitation**

et al. 2020

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A 4‐amino‐2,2,6,6‐tetramethyl‐1‐piperidinyloxyl (TEMPO) radical was attached to the bay position of perylene‐3,4 : 9,10‐bis(dicarboximide) (perylenebisimide, PBI) to study the radical‐enhanced intersystem crossing (REISC) and electron spin dynamics of the photo‐induced high‐spin states. The dyads give strong visible light absorption (ϵ=27000 M−1 cm−1at 607 nm). Attaching a TEMPO radical to the PBI unit transforms the otherwise non‐radiative decay of S1 state (fluorescence quantum yield: ΦF=2.9 %) of PBI unit to ISC (singlet oxygen quantum yield: ΦΔ=31.8 %, ΦF=1.6 %). Moreover, the REISC is more efficient as compared to the heavy atom effect‐induced ISC (ΦΔ=17.8 % for 1,8‐dibromoPBI). For the dyad, ISC takes 245 ps and triplet state lifetime is 1.5 μs, much shorter than the native PBI (τT=126.6 μs). X‐ and Q‐band time‐resolved electron paramagnetic resonance spectroscopy shows that the exchange interaction in the photoexcited radical‐chromophore dyad is larger than the triplet zero‐field splitting (ZFS) and the difference of Zeeman energies of the radical and chromophore. The inversion of electron spin polarization from emissive to absorptive was observed and attributed to the initial completion of the quartet state population and the subsequent depopulation processes induced by the zero‐field splitting.

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Section: Resultscontrasting

confidence: 98%

Section: Resultsmentioning

confidence: 87%

Radical‐Enhanced Intersystem Crossing in a Bay‐Substituted Perylene Bisimide−TEMPO Dyad and the Electron Spin Polarization Dynamics upon Photoexcitation**

et al. 2020

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“…The data were analyzed with single value decomposition (SVD) and global fitting, employing a linear unidirectional decay scheme, obtaining the time constants and the Evolution Associated Difference Spectra (EADS). In previously reported radical‐containing molecules, for instance, NDI labeled with TEMPO, the ISC occurs within 338 ps, [7] whereas for the NDI‐veradazyl dyad a charge recombination‐induced ISC was observed (time constant: 1.40 ps), instead of the expected electron spin‐spin exchange interaction‐induced ISC [41] . Furthermore, in the compact perylene‐NO⋅ dyad, the REISC takes place within 1 ps [26] .…”

Section: Resultsmentioning

confidence: 84%

“…The fluorescence spectra of the dyads were also measured in solvents of different polarities, the results indicated that the emission is quenched in all solvents compared with the pristine perylene (Figure S24 and S25 in the Supporting Information). The strong quenching of the perylene fluorescence in the dyads can be ascribed to different reasons, including Förster Resonance Energy Transfer (FRET) towards the verdazyl moiety, photoinduced electron transfer (PET), spin‐spin exchange interactions to form high spin states or radical enhanced ISC [7,41,44–46] …”

Section: Resultsmentioning

confidence: 99%

Radical‐Enhanced Intersystem Crossing in Perylene‐Oxoverdazyl Radical Dyads

et al. 2022

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Attaching stable radicals to organic chromophores is an effective method to enhance the intersystem crossing (ISC) of the chromophores. Herein we prepared perylene-oxoverdazyl dyads either by directly connecting the two units or using an intervening phenyl spacer. We investigated the effect of the radical on the photophysical properties of perylene and observed strong fluorescence quenching due to radical enhanced ISC (REISC). Compared with a previously reported perylene-fused nitroxide radical compound (triplet lifetime, τ T = 0.1 μs), these new adducts show a longer-lived triplet excited state (τ T = 9.5 μs). Based on the singlet oxygen quantum yield (Φ Δ = 7 %) and study of the triplet state, we propose that the radical enhanced internal conversion also plays a role in the relaxation of the excited state. Femtosecond fluorescence up-conversion indicates a fast decay of the excited state (< 1.0 ps), suggesting a strong spin-spin exchange interaction between the two units. Femtosecond transient absorption (fs-TA) spectra confirmed direct triplet state population (within 0.5 ps). Interestingly, by fs-TA spectra, we observed the interconversion of the two states (D 1 $ Q 1 ) at ~80 ps time scale. Time-resolved electron paramagnetic resonance (TREPR) spectral study confirmed the formation of the quartet sate. We observed triplet and quartet states simultaneously with weights of 0.7 and 0.3, respectively. This is attributed to two different conformations of the molecule at excited state. DFT computations showed that the interaction between the radical and the chromophore is ferromagnetic (J > 0, 0.05 ~0.10 eV).

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“…Nowadays, mode-locked Ti:sapphire lasers can routinely provide highly stable pulses, even as short as about 4 fs. The resulting fundamental 800 nm laser mode can be efficiently tuned in the UV and visible spectral region in order to provide suitable pump wavelengths [7,[21][22][23]. The wide tunability is accomplished by means of OPA (Optical Parametric Amplification), OPG (Optical Parametric Generation) or by Second Harmonic (SHG) and Third Harmonic (THG) Generation.…”

Section: Basic Principles Of Transient Absorption Spectroscopy (Tas) mentioning

confidence: 99%

Synergistic Approach of Ultrafast Spectroscopy and Molecular Simulations in the Characterization of Intramolecular Charge Transfer in Push-Pull Molecules

et al. 2020

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The comprehensive characterization of Intramolecular Charge Transfer (ICT) stemming in push-pull molecules with a delocalized π-system of electrons is noteworthy for a bespoke design of organic materials, spanning widespread applications from photovoltaics to nanomedicine imaging devices. Photo-induced ICT is characterized by structural reorganizations, which allows the molecule to adapt to the new electronic density distribution. Herein, we discuss recent photophysical advances combined with recent progresses in the computational chemistry of photoactive molecular ensembles. We focus the discussion on femtosecond Transient Absorption Spectroscopy (TAS) enabling us to follow the transition from a Locally Excited (LE) state to the ICT and to understand how the environment polarity influences radiative and non-radiative decay mechanisms. In many cases, the charge transfer transition is accompanied by structural rearrangements, such as the twisting or molecule planarization. The possibility of an accurate prediction of the charge-transfer occurring in complex molecules and molecular materials represents an enormous advantage in guiding new molecular and materials design. We briefly report on recent advances in ultrafast multidimensional spectroscopy, in particular, Two-Dimensional Electronic Spectroscopy (2DES), in unraveling the ICT nature of push-pull molecular systems. A theoretical description at the atomistic level of photo-induced molecular transitions can predict with reasonable accuracy the properties of photoactive molecules. In this framework, the review includes a discussion on the advances from simulation and modeling, which have provided, over the years, significant information on photoexcitation, emission, charge-transport, and decay pathways. Density Functional Theory (DFT) coupled with the Time-Dependent (TD) framework can describe electronic properties and dynamics for a limited system size. More recently, Machine Learning (ML) or deep learning approaches, as well as free-energy simulations containing excited state potentials, can speed up the calculations with transferable accuracy to more complex molecules with extended system size. A perspective on combining ultrafast spectroscopy with molecular simulations is foreseen for optimizing the design of photoactive compounds with tunable properties.

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

Cited by 13 publications

References 59 publications

Radical‐Enhanced Intersystem Crossing in a Bay‐Substituted Perylene Bisimide−TEMPO Dyad and the Electron Spin Polarization Dynamics upon Photoexcitation**

Radical‐Enhanced Intersystem Crossing in a Bay‐Substituted Perylene Bisimide−TEMPO Dyad and the Electron Spin Polarization Dynamics upon Photoexcitation**

Radical‐Enhanced Intersystem Crossing in Perylene‐Oxoverdazyl Radical Dyads

Synergistic Approach of Ultrafast Spectroscopy and Molecular Simulations in the Characterization of Intramolecular Charge Transfer in Push-Pull Molecules

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