Asymmetric-donor (D2D2′)–acceptor (A) conjugates for simultaneously accessing intrinsic blue-RTP and blue-TADF

Abstract

The development of new photoluminescent (PL) materials with simultaneous room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) features is highly desirable for bio-imaging, security applications and sensors due to the involvement of both singlet and longer-lived triplet states. Here, we report two carbazolyl-phenoxy-phthalonitrile conjugates (CPPN, CPPNF). Spectroscopic studies combining two daughter compounds (PPN, PPNF) in polar and nonpolar hosts confirmed efficient blue-RTP from the higher-energy triplet state (T_PPN) due to the phenoxy-phthalonitrile (PPN) part, and blue-TADF via reverse intersystem crossing from the low-lying triplet state (T_CzPN) of the carbazolyl-phthalonitrile (CzPN) part to the singlet (S₁) state of the same CzPN part, utilizing the T_PPN state that acts as an intermediate for spin–vibronic coupling. Such PL characteristics are observed due to the energetic proximity of ³LE_PPN, ¹CT_CzPN and ³CT_CzPN. In the hydrogen-bonded matrix and crystals, we found faint persistent green-RTP characteristics of the PPNF due to supramolecular interactions and aggregation of the molecule. This study could pave the way to understanding the involvement of different excited states associated with TADF and RTP processes of asymmetric-donor–acceptor systems.