Room Temperature NIR Phosphorescence from C64 Nanographene Tetraimide by π-Stacking Complexation with Pt(II)Porphyrin

Additional data to report https://doi.org/10.1002/anie.202406353:

Near Infrared (NIR) phosphorescence at room temperature is challenging to achieve for organic molecules due to a 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 C₆₄ nanographene tetraimide 1. ¹H 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 S₁ and T₃ 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.