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. In this work we have systematically designed two multiple donors and single acceptor based molecular systems which can simultaneously harness the triplet state via two different channels. We designed the molecules by taking cue from the idea that the free lone pair of electron containing phenoxy donors when linked to the phthalonitrile (PN) acceptor gives rise to RTP emission. When carbazole connects angularly with PN acceptor, it give rise to TADF emission. In this work we have connected both the donors to the single acceptor PN. Here we discuss the photophysical studies of two carbazolyl-phenoxy-phthalonitrile conjugates (CPPN, CPPNF). The detailed spectroscopic studies of CPPN and CPPNF along with two daughter compounds of phenoxy-phthalonitrile (PPN, PPNF) in polar and non-polar hosts confirmed efficient blue-RTP from the higher-energy locally excited (LE) triplet state (TPPN) due to the phenoxy-phthalonitrile (PPN) part. While the blue-TADF was observed via the reverse intersystem crossing from the low-lying charge transfer triplet state (TCzPN) of the carbazolyl-phthalonitrile (CzPN) part to the singlet (S1) charge transfer state of the same CzPN part. Moreover, it was observed that the higher lying LE triplet state (TPPN) acts as an intermediate for spin–vibronic coupling to cause the reverse intersystem crossing. Such PL characteristics are observed due to the energetic proximity of 3LEPPN, 1CTCzPN and 3CTCzPN. 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 paves the way to understand the involvement of different excited states associated with TADF and RTP processes of asymmetric-donor–acceptor systems.

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

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