Ultrafast charge-transfer dynamics of donor-substituted truxenones

Abstract

The photophysics of two donor-substituted truxenone derivatives has been studied by femtosecond time-resolved transient absorption spectroscopy. The systems consist of a central truxenone acceptor with three triarylamine (TARA) branches which act as electron donors. Upon excitation in the visible regime an electron is transferred from the donor to the acceptor, generating a charge-separated state. This state can be probed via the characteristic absorption of the TARA radical cation around 700 nm. A second absorption band around 420 nm exhibits the same kinetics and is assigned to an absorption of the radical anion of the truxenone moiety. The back electron transfer and the recovery of the ground state can be interpreted within the framework of Marcus theory. To study the dependence of the back electron transfer on the electronic coupling, the distance between the donor and the acceptor was adjusted. Two solvents were employed, dimethylsulfoxide and dichloroethane. A biexponential decay of the bands assigned to the charge-separated state was observed, with time constants in the picosecond range. Surprisingly, the rates for electron back transfer do not follow the simple picture of the donor-acceptor distance being the determining factor. The observations are explained within a model that additionally takes steric interactions between the donor and the acceptor into account.

Time-Domain Study of the S3 State of 9-Fluorenone

“…Second, its photochemistry is of relevance for optoelectronics: Polyfluorenes have been investigated as possible materials for polymer light emitting diodes (PLEDS). − However, oxidative damage of fluorene units generating 9-fluorenone changes the emission properties of the polymer. , This limits its color stability and as a consequence polyfluorenes become less attractive for applications. , Recently, 9-fluorenone itself showed to be relevant for material science and was incorporated in dye-sensitized solar cells. , A further motivation for us is the fact that fluorenone is a building block of the truxenone electron acceptor . Donor–acceptor systems with truxenone have been studied because they might also be of interest for applications in nonlinear optics. − …”

Optically induced charge-transfer in donor-acceptor-substituted p- and m- C2B10H12 carboranes

“…In THF, the ESA signals are very similar to those in hexane, suggesting an ICT character of DA- p Carb in both solvents. Vibrational cooling with τ = 2.2 ps in THF is accompanied by a small hypsochromic shift of the ESA band of the first EADS at 680 nm, confirming the strong solvation effect of the CT state in polar solvents 57 . The cold S 1 state has a lifetime of 20.5 ns, which agrees with the fluorescence lifetime of DA- p Carb in THF.…”

“…The empty p z orbital at boron makes the BMes 2 group a strong π-acceptor and the mesityl groups provide good stability by steric shielding 47 – 56 . Triarylamine is used as the electron donor due to its strong π-electron-donating ability and the low reorganization energy of the amine group supports rapid charge transfer processes 51 , 57 , 58 . The synthesis of all compounds are summarized in the SI (Supplementary Fig.…”

Ultrafast photophysics of an orange–red thermally activated delayed fluorescence emitter: the role of external structural restraint

“…64,65 For the subsequent delay times of 1 ps to 1 ns, fs-TA evolution visualizes wavepacket motion that highly depends on the topology of S 1 PES. 41,[66][67][68] For instance, the role of the excited-state structural relaxation (ES-SR) in the S 1 state decay of DA-and DAD/ADA-type TADF emitters has been intensively reported. [69][70][71][72][73] Suffering from the poor structural sensitivity of UV/Vis fs-TA, S 1 /S 0 ES-SR usually leads to minimized alternation of the ESA shape, which is consistent with the observed fs-TA of TDBA-Ac and PzTDBA for 1 ps to 1 ns delay times.…”