Electronic coupling and spin–orbit charge transfer intersystem crossing (SOCT-ISC) in compact BDP–carbazole dyads with different mutual orientations of the electron donor and acceptor

Abstract

In order to study the spin–orbit charge transfer induced intersystem crossing (SOCT-ISC), Bodipy (BDP)–carbazole (Cz) compact electron donor/acceptor dyads were prepared. Charge transfer (CT) emission bands were observed for dyads showing strong electronic coupling between the donor and the acceptor (coupling matrix elements VDA, 0.06 eV–0.18 eV). Depending on the coupling magnitude, the CT state of the dyads can be either dark or emissive. Equilibrium between the 1LE (locally excited) state and the 1CT state was confirmed by temperature-dependent fluorescence studies. Efficient ISC was observed for the dyads with Cz connected at the meso-position of the BDP. Interestingly, the dyad with non-orthogonal geometry shows the highest ISC efficiency (ΦΔ = 58%), which is different from the previous conclusion. The photo-induced charge separation (CS, time constant: 0.7 ps) and charge recombination (CR, ∼3.9 ns) were studied by femtosecond transient absorption spectroscopy. Nanosecond transient absorption spectroscopy indicated that the BDP-localized triplet state was exceptionally long-lived (602 µs). Using pulsed laser excited time-resolved electron paramagnetic resonance spectroscopy, the SOCT-ISC mechanism was confirmed, and we show that the electron spin polarization of the triplet state is highly dependent on the mutual orientation of the donor and acceptor. The dyads were used as triplet photosensitizers for triplet–triplet-annihilation (TTA) upconversion, and the quantum yield is up to 6.7%. TTA-based delayed fluorescence was observed for the dyads (τDF = 41.5 µs). The dyads were also used as potent photodynamic therapy reagents (light toxicity of IC50 = 0.1 µM and dark toxicity of IC50 = 70.8 µM).

Twisted BODIPY derivative: intersystem crossing, electron spin polarization and application as a novel photodynamic therapy reagent

“…−82 mT), which are without extended πconjugation framework. 65,66 Most reasonably, this that the unpaired electrons of the triplet state in BDP-1 are with larger separation, i.e. more delocalized on the π-conjugated framework.…”

Intersystem Crossing and Electron Spin Selectivity in Anthracene‐Naphthalimide Compact Electron Donor‐Acceptor Dyads Showing Different Geometry and Electronic Coupling Magnitudes

“…Note that the observed D, E values are drastically different from those of naphthalimide (NI) spectrum; therefore, the localization of triplet on anthracene moiety is confirmed. At the same time, anthracene itself shows (e, e, e, a, a, a) ESP pattern, [26,80,81] whereas both 2-An-NI and 9- An-NI have different ESP of (e, a, e, a, e, a) in case of 2-An-NI and (a, a, e, a, e, e) in case of 9-An-NI, respectively. Therefore, the mechanism of triplet formation in these two dyads is most reasonably SOCT-ISC (Table 4).…”

Dual emission in purely organic materials for optoelectronic applications

“…4(a)), which was retained at various temperatures in solvents of different polarity. 46 In turn, peculiar DE from two singlet states in 2 was observed in violation of Kasha's rule. 18 DE in 2 was accompanied by a negligible structural rearrangement upon electronic excitation and subsequent relaxation, and optimal energy gaps of the two optical bands (S 02 and S 01 ) with fast (200 fs) internal conversion (S 2 -S 1 ) lead to decoupled relaxation and simultaneous radiative decay from both S 2 and S 1 .…”