Platinum Complexes of <i>N</i>,<i>N</i>′,<i>N</i>″,<i>N</i>‴‑Diboronazophenines

Azophenine, (α-C<sub>6</sub>H<sub>5</sub>NH)<sub>2</sub>(C<sub>6</sub>H<sub>5</sub>–NC<sub>6</sub>H<sub>2</sub>N–C<sub>6</sub>H<sub>5</sub>), well known to be non-emissive, was rigidified by replacing two amine protons by two difluoroboranes (BF<sub>2</sub><sup>+</sup>) and further functionalized at the <i>para</i>-positions of the phenyl groups by luminescent <i>trans</i>-ArCC–Pt­(PR<sub>3</sub>)<sub>2</sub>-CC (<b>[Pt]</b>) arms [Ar = C<sub>6</sub>H<sub>4</sub> (R = Et), hexa­(<i>n</i>-hexyl)­truxene) (<b>Tru</b>; R = Bu)]. Two effects are reported. First, the linking of these <b>[Pt]</b> arms with the central azophenine (C<sub>6</sub>H<sub>4</sub>–NC<sub>6</sub>H<sub>2</sub>(NH)<sub>2</sub>N–C<sub>6</sub>H<sub>4</sub>; <b>Q</b>) generates very low energy charge-transfer (CT) singlet and triplet excited states (<sup>3,1</sup>(<b>[Pt]</b>-to-<b>Q</b>)*) with absorption bands extending all the way to 800 nm. Second, the rigidification of azophenine by the incorporation of BF<sub>2</sub><sup>+</sup> units renders the low-lying CT singlet state clearly emissive at 298 and 77 K in the near-IR region. DFT computations place the triplet emission in the 1200–1400 nm range, but no phosphorescence was detected. The photophysical properties are investigated, and circumstantial evidence for slow triplet energy transfers, <sup>3</sup><b>Tru</b>* → <b>Q</b>, is provided.