Hybridization of short-range and long-range charge transfer boosts room-temperature phosphorescence performance

Abstract

At present, mainstream room-temperature phosphorescence (RTP) emission relies on organic materials with long-range charge-transfer effects; therefore, exploring new forms of charge transfer to generate RTP is worth studying. In this work, indole-carbazole was used as the core to ensure the narrowband fluorescence emission of the material based on its characteristic short-range charge-transfer effect. In addition, halogenated carbazoles were introduced into the periphery to construct long-range charge transfer, resulting in VTCzNL-Cl and VTCzNL-Br. By encapsulating these phosphors into a robust host (TPP), two host-guest crystalline systems were further developed, achieving efficient RTP performance with phosphorescence quantum yields of 26% and phosphorescence lifetimes of 3.2 and 39.2 ms, respectively.

Fig. 1. Molecular design strategies and electron cloud distribution of the HOMO and LUMO for the case study of VTCzNL-Cl.

Fig. 2. (a) Crystal packing of VTCzNL-Cl. (b) Crystal packing of VTCzNL-Br showing H-aggregation.

Fig. 3. UV-vis absorption and fluorescence emissions of VTCzNL-Cl (a) and VTCzNL-Br (b).

Fig. 4. HOMO and LUMO electron cloud distribution patterns.

Fig. 5. (a) Room-temperature fluorescence and phosphorescence spectra of the VTCzNL-Cl-based complex. (b) Transient lifetime of the VTCzNL-Cl-based complex. (c) Cocrystal obtained by dissolving VTCzNL-Cl in the TPP host and photos taken of this before and after 365 nm UV lamp irradiation. (d) Room-temperature fluorescence and phosphorescence spectra of the VTCzNL-Br-based complex. (e) Transient lifetime of the VTCzNL-Br-based complex. (f) Cocrystal obtained by dissolving VTCzNL-Br in the TPP host and its photos taken before and after 365 nm UV lamp irradiation.