Molecular Engineering of Asymmetric-Donors(D2D2′)-Acceptor(A) Conjugates Enables Blue-RTP with Persistent Green-RTP Characteristics, and Blue-TADF

Developing 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 (TPPN) due to phenoxy-phthalonitrile (PPN) part, and blue-TADF via reverse intersystem crossing from the low-lying triplet state (TCzPN) of the carbazolyl-phthalonitrile (CzPN) part to the singlet (S1) state of the same CzPN part, utilizing the TPPN state that acts as an intermediate for spin-vibronic coupling. Such PL characteristics are observed due to energetic proximity of 3LEPPN, 1CTCzPN and 3CTCzPN. In hydrogen-bonded matrix and crystals, we found faint persistent green-RTP characteristic of the PPNF due to supramolecular interactions and aggregation of the molecule. This study could pave the way to understand the involvement of different excited states associated in TADF and RTP processes of asymmetric-donors-acceptor systems.