Direct Observation of Ultrafast Access to a Solvent-Independent Singlet–Triplet Equilibrium State in Acridone Solutions

Abstract

Acridone and its derivatives have potential application as emitters for highly efficient blue organic light-emitting diodes (OLEDs). In this paper, we demonstrated ultrafast access of a solvent-independent singlet−triplet equilibrium state in acridone solutions by using femtosecond time-resolved spectroscopy. Our spectral data show that due to highly effective forward and reverse intersystem crossing (both k ISC and k rISC over 10 10 s −1 ), a singlet−triplet equilibrium state is always populated in acridone in all solvents studied. However, the lifetimes of the equilibrium state varied a lot in different solvent environments and the final decay pathway of this state can switch between high quantum yield fluorescence emission and further internal conversion to the lowest triplet state. These findings provide direct experimental evidence to understand the distinct photophysical behaviors of acridone and also provide guidance for further design of acridone and its derivatives as blue OLED emitters.

Structure and Electron Configuration of Imidazole-2-carboxaldehyde and Its Excited Triplet: Resonance Raman and Transient Absorption Spectroscopy and DFT Calculation Investigations

“…Their electron configuration was carefully examined and revealed with nπ* and ππ*character, respectively. These results indicate that the intersystem crossing can proceed efficiently via the pathway of S 2 → S 1 → T 1 (ππ*), which is consistent with the results from QM/MM molecular dynamics simulations and high-level ab initio calculations, and ultrafast spectroscopic experiments for analog aromatic carbonyls. − A surface-crossing point T 2 /T 1 with the energy of 77.2/77.3 kcal/mol was located, indicating that the nπ* and ππ* triplets are in equilibrium. Given that the computed energies were obtained in the gas phase and the fact that the polar solvent can stabilize the ππ* state, the nπ* triplet may have a minor population.…”

Photochemical acridone-mediated direct arylation of (hetero)arenes with aryl diazonium salts

“…17 Chen et al demonstrated ultrafast access to a singlet–triplet equilibrium state in all the acridone solutions studied, elucidating the unique photophysical behaviour of acridone. 18 Inspired by these preceding observations, we propose a photo-induced direct arylation of arenes and heteroarenes with aryl diazonium salts, triggered by the relatively inexpensive catalyst acridone.…”

Shifting multi-resonance to dipolar intramolecular charge-transfer fluorescence by Lewis acid–base Interactions

“…[2][3][4] The benefits offered by acridone fluorophores are enormous: in contrast to the synthetically challenging B/N-based molecules, acridone derivatives can be readily synthesized. 5 In addition, the carbonyl group generates the n-p* transition state, [6][7][8] which provides an exciton-harvest channel that is quantum chemically allowed by the El-Sayed rule. 9 Notable successes involve quinolino[3,2,1-de]acridine-5,9dione.…”