Stable Iminium Singlet and Triplet Diradical(oid)s with Intense NIR‐II Absorptions

This study presents the successful synthesis of a series of stable iminium diradical(oid)s. CNR1⁺OTf^-, CNR2⁺OTf^-, and CNR3⁺OTf^- can be readily prepared by treating their corresponding methoxy precursors with triflate acid. Remarkably, they all display excellent stability under light and ambient conditions. CNR1⁺ exhibits a closed shell electronic feature, whereas CNR2⁺ features an open shell singlet ground state. CNR3⁺OTf^- possess triplet ground electronic state, as evidenced by ESR and superconducting quantum interference device (SQUID) measurements. Through meticulous fitting of the SQUID data, a singlet-triplet energy gaps (∆E_S-T) of +1.04 kcal mol^-1 along with intermolecular antiferromagnetic interactions (θ) of -28 K were obtained. In comparison to CNR1⁺, both the open shell CNR2⁺ and CNR3⁺ display distinctively red shifted long wavelength absorption bands that extend up to approximately 2400 nm. Such long wavelength absorption characteristics are quite scarce among organic materials. This research offers a novel approach for the design and synthesis of iminium diradical(oid)s, which feature tunable ground states and exhibit intense absorption in the second near infrared (NIR-II) region, opening up new possibilities in the field of organic materials research.