Browsing by Author "Debnath, S."

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    A Twist in biphthalimide-based chromophores enables thermally activated delayed fluorescence
    (American Chemical Society, 2024-04-18) Debnath, S.; Ramkissoon, P.; Vonder Haar, A.L.; Salzner, Ulrike; Smith, T.A.; Musser, A.J.; Patil, S.
    Thermally activated delayed fluorescence (TADF) emitters, which convert nonemissive triplets into emissive singlets, have garnered tremendous impetus as next-generation organic electroluminescent materials. Employing donor−acceptor (D−A) designs to produce intramolecular charge transfer (ICT) states is considered an attractive strategy to effectively reduce the singlet− triplet (ΔEST) gap, thereby enhancing reverse intersystem crossing (rISC) in TADF emitters. Herein, we report two ICT chromophores (BP-1TPA and BP-2TPA) utilizing a rational design strategy based on a twisted biphthalimide acceptor core integrated with varying triphenylamine donors. We accomplish efficient TADF emission with a high photoluminescence quantum yield (PLQY) of ∼80% at ambient conditions from poly(methyl methacrylate)-doped films of these chromophores. Twisting the acceptor core ensures the separation of natural transition orbitals, leading to small ΔEST and generates an intermediate triplet excited state to facilitate rISC. The present study, therefore, sheds light on how delayed fluorescence can be realized from a simple twisted phthalimide core by rational molecular engineering and enables new insights toward exploring the aromatic imide class of molecules as potential organic light-emitting materials.
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    Deciphering intramolecular charge transfer in fluoranthene derivatives
    (Royal Society of Chemistry, 2024-05-24) Debnath, S.; Mohanty, A.; Naik, P.; Salzner, Ulrike; Dasgupta, J.; Patil, S.
    An intramolecular charge transfer (ICT) state evolves via excited state structural change and solvent reorganization, where the charge distribution in the excited state is markedly different from that in the ground state. Due to its ubiquitous nature, this intriguing photophysical phenomenon offers promising applications in the realm of optoelectronics. Judicious choice of donor-acceptor-based (D-A) push-pull chromophores is the most fundamental strategy to achieve ICT state formation. In the present work, we introduce a unique class of fluoranthene-based chromophores that do not belong to the conventional D-A design principle, as the fluoranthene core is seldom used as an acceptor. Nevertheless, we observe ICT state formation upon attaching strong donor triphenylamine to the fluoranthene backbone (TPF-2TPA). Theoretical studies demonstrate that the hole and electron densities are localized over the triphenylamine and fluoranthene core, respectively, which induces ICT character in the lowest energy transition of TPF-2TPA. Solvent polarity-dependent steady-state and time-resolved spectroscopic studies confirm the formation of the ICT state. Furthermore, viscosity-dependent study of TPF-2TPA reveals the involvement of a structural relaxation during ICT state formation. The present study sheds light on the rational design of unconventional ICT chromophores based on fluoranthene, thereby widening the applications of fluoranthene-based molecular systems in optoelectronic devices.