D−A−D based pyrido-pyrazino[2,3-b]indole amines as blue-red fluorescent dyes: Photophysical, aggregation-induced emission, electrochemical and theoretical studies

Herein donor−acceptor−donor (D−A−D) structured, pyridopyrazino[2,3-b]indole amines 2–6 were designed and synthesized via C–N coupled Buchwald-Hartwig amination reaction and characterized by spectroscopic methods. C–N coupling in molecules offers intramolecular charge transfer (ICT) transitions at longer wavelengths (λmax = 400–459 nm) in absorption spectra reminiscent D−A assembly. Dyes covers broad range of emission and emit in blue to red region with emission maxima 433–600 nm in solvent and solid film. Dyes 2, 5 and 6 explore the aggregation-induced emission (AIE) characteristics. Further C–N blending of various donor with pyridopyrazino[2,3-b]indole acceptor results in suppressed band gap (1.99–2.43 eV) and comparable HOMO (−5.17 to −5.71 eV) and LUMO (−3.18 to −3.28 eV) energies with reported small organic ambipolar materials. DFT and TDDFT calculations agree with the experimental opto-electrochemical data. Moreover, computed small singlet and triplet excitation energy difference (ΔEST (0.01–0.14 eV)) suggest thermally activated delayed fluorescent (TADF) emitting properties of dyes. Thus pyridopyrazino[2,3−b]indole amine dyes propose their potential application in optoelectronic devices.