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 (∆ES-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.