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

Abstract

Azophenine,\n(α-C₆H₅NH)₂(C₆H₅–NC₆H₂N–C₆H₅), well known to be non-emissive, was rigidified\nby replacing two amine protons by two difluoroboranes (BF₂⁺) and further functionalized at the <i>para</i>-positions of the phenyl groups by luminescent <i>trans</i>-ArCC–Pt­(PR₃)₂-CC (<b>[Pt]</b>) arms [Ar = C₆H₄ (R = Et), hexa­(<i>n</i>-hexyl)­truxene) (<b>Tru</b>; R = Bu)]. Two effects\nare reported. First, the linking of these <b>[Pt]</b> arms with\nthe central azophenine (C₆H₄–NC₆H₂(NH)₂N–C₆H₄; <b>Q</b>) generates very low energy charge-transfer\n(CT) singlet and triplet excited states (^3,1(<b>[Pt]</b>-to-<b>Q</b>)*) with absorption bands extending all the way\nto 800 nm. Second, the rigidification of azophenine by the incorporation\nof BF₂⁺ units renders the low-lying CT singlet\nstate clearly emissive at 298 and 77 K in the near-IR region. DFT\ncomputations place the triplet emission in the 1200–1400 nm\nrange, but no phosphorescence was detected. The photophysical properties\nare investigated, and circumstantial evidence for slow triplet energy\ntransfers, ³<b>Tru</b>* → <b>Q</b>,\nis provided.