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Conjugated π-extended Tryptanthrins with potential optoelectronic applications: Synthesis, electrochemical and Photophysical studies
Authors: Cláudia Alves; Vitor A.S. Almodovar; João P. Prates Ramalho; Ana C. Amorim; Paulo D. Nunes Barradas; J. António Paixão; J. Sérgio Seixas de Melo; Anthony J. Burke
Ref.: J. Photochem. Photobiol. A: Chem. 484, 117742 (2026)
Abstract: Tryptanthrins are a class of golden-yellow pi-conjugated compounds consisting of a quinazoline ring fused to an indole moiety, with carbonyl groups at the 6- and 12-positions that confer electron-acceptor properties. The possibility of introducing electron-donating (ED) groups into their core (at the 2- and 8-positions) makes these compounds suitable for a wide range of optoelectronic applications. In this work, we use Pd-catalyzed couplings to introduce key conjugated ED units (carbazole (ca), dibenzothiophene (dbz) and naphthalene (np)) to achieve pi-expansion of the tryptanthrin core. (Donor)D-A(Acceptor) and D-A-D type systems were developed. A comprehensive photophysical characterization, including absorption and emission spectroscopy and fluorescence life-time studies, was performed for all compounds to identify the derivative with the most suitable properties for optoelectronic applications. The results show that stronger ED groups produce a marked decrease in fluorescence lifetime, whereas less ED substituents, such as dbz andnp, lead to increased fluorescence lifetimes with increasing solvent polarity. The HOMO-LUMO gaps, determined by high level DFT, were in agreement with those measured using cyclic voltammetry, indicating their suitability for optoelectronic applications (the carbazole substituted analogues are the most appropriate). In addition, DFT calculations were carried out to understand the chargetransfer characteristics and photochemical behaviour of these compounds.
