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

Abstract 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.