Room‐Temperature Near‐Infrared Phosphorescence from C 64 Nanographene Tetraimide by π‐Stacking Complexation with Platinum Porphyrin

Near‐Infrared (NIR) phosphorescence at room temperature is challenging to achieve for organic molecules due to negligible spin–orbit coupling and a low energy gap leading to fast non‐radiative transitions. Here, we show a supramolecular host–guest strategy to harvest the energy from the low‐lying triplet state of C 64 nanographene tetraimide 1 . 1 H NMR and X‐ray analysis confirmed the 1 : 2 stoichiometric binding of a Pt(II) porphyrin on the two π‐surfaces of 1 . While the free 1 does not show emission in the NIR, the host–guest complex solution shows NIR phosphorescence at 77 K. Further, between 860–1100 nm, room temperature NIR phosphorescence ( λ max =900 nm, τ avg =142 μs) was observed for a solid‐state sample drop‐casted from a preformed complex in solution. Theoretical calculations reveal a non‐zero spin–orbit coupling between isoenergetic S 1 and T 3 of π‐stacked [ 1 ⋅ Pt(II) porphyrin] complex. External heavy‐atom‐induced spin–orbit coupling along with rigidification and protection from oxygen in the solid‐state promotes both the intersystem crossing from the first excited singlet state into the triplet manifold and the NIR phosphorescence from the lowest triplet state of 1 .