Spiro Rhodamine-Perylene Compact Electron Donor–Acceptor Dyads: Conformation Restriction, Charge Separation, and Spin–Orbit Charge Transfer Intersystem Crossing

Abstract

Spiro rhodamine (Rho)-perylene (Pery) electron donor−acceptor dyads were prepared to study the spin−orbit charge transfer intersystem crossing (SOCT-ISC) in these rigid and sterically congested molecular systems. The electron-donor Rho (lactam form) moiety is attached via the N−C bond to the electron acceptor at either 1-or 3-position of the Pery moiety (Rho-Pery-1 and Rho-Pery-3). Severe torsion of the Pery moiety in Rho-Pery-1 was observed. The fluorescence of the two dyads is significantly quenched in polar solvents, and the singlet oxygen quantum yields (Φ Δ ) are strongly dependent on solvent polarity (4−36%). Femtosecond transient absorption spectra demonstrate that charge separation (CS) takes 0.51 ps in Rho-Pery-1 and 5.75 ps in Rho-Pery-3, and the charge recombination (CR)-induced ISC is slow (>3 ns). Nanosecond transient absorption spectra indicate that the formation of triplet states via SOCT-ISC takes 24−75 ns for Rho-Pery-1 and 6−15 ns for Rho-Pery-3, and the distorted π-framework of the Pery moiety results in a shorter triplet lifetime of 19.9 vs 291 μs for the planar analogue. Time-resolved electron paramagnetic resonance spectroscopy confirms the SOCT-ISC mechanism.

Merging of a Perylene Moiety Enables a RuII Photosensitizer with Long‐Lived Excited States and the Efficient Production of Singlet Oxygen

“…The ipPer ligand exhibits an absorption maximum at around 457 nm without a characteristic vibronic fine structure, which is otherwise typical of a perylene chromophore. [62] Furthermore, its absorption profile is red-shifted of about 15 nm compared to bare perylene. [62] With a molar extinction coefficient of ɛ = 50.3 • 10 3 M À 1 cm À 1 at 467 nm the absorptivity of RuipPer corresponds well to the sum of perylene π-π* (37.0 • 10 3 M À 1 cm À 1 ) [62] and Ru II metal-toligand charge transfer (MLCT) transitions (17.5 10 3 M À 1 cm À 1 ) [60] indicating the multichromophoric behavior of this novel complex.…”

“…[62] Furthermore, its absorption profile is red-shifted of about 15 nm compared to bare perylene. [62] With a molar extinction coefficient of ɛ = 50.3 • 10 3 M À 1 cm À 1 at 467 nm the absorptivity of RuipPer corresponds well to the sum of perylene π-π* (37.0 • 10 3 M À 1 cm À 1 ) [62] and Ru II metal-toligand charge transfer (MLCT) transitions (17.5 10 3 M À 1 cm À 1 ) [60] indicating the multichromophoric behavior of this novel complex. The intense absorption between 400 and 500 nm is again slightly red-shifted by 10 nm compared to both bare perylene and [(tbbpy) 2 Ru(ip)] 2 + .…”

Electron Spin Dynamics of the Intersystem Crossing of Triplet Photosensitizers That Show Strong Absorption of Visible Light and Long-Lived Triplet States

“…We prepared the dyads based on the spiro structure with NI or perylene as the electron acceptor (Figure 6). 47,48 For RB-NI, with nanosecond transient absorption spectroscopy, we observed a CT state with a lifetime of 0.93 μs in fluid hexane solution at room temperature. 47 However, with TREPR spectra (in frozen solution of toluene/2-methyltetrahydrofuran at 80 K, or in E7 liquid crystal), only a 3 LE state localized on the NI moiety was observed, the difference between the two spectral results can be attributed to the different experimental conditions.…”

“…We prepared the dyads based on the spiro structure with NI or perylene as the electron acceptor (Figure ). , …”

“…B 0 ⊥ L and B 0 L indicate that the polarization directions of the laser ( L ) were perpendicular and parallel to the magnetic field ( B 0 ), respectively. Reproduced with permission from ref . Copyright 2021, American Chemical Society.…”