Modulation of 9,12‐Substituted o ‐Carboranes Toward Anti‐Kasha Triple‐Fluorescence

ABSTRACT Achieving triple‐fluorescence from a pure organic compound in solution is nearly impossible, as Kasha's rule only allows single fluorescence from the lowest excited state. In this paper, pyrene‐substituted o ‐carboranes, 1a ‐ c , and 2a , were synthesized within 3–5 steps from commercially available chemicals, and their chemical structures have been confirmed by 1 H NMR, 13 C NMR, and HRMS. The photophysical properties of these compounds have been studied in detail by UV–vis, steady and transient state fluorescence, temperature‐dependent fluorescence, and femtosecond transient absorption spectroscopy, as well as TD‐DFT calculations. The results show that while 2a exhibits only local emission, the B,B‐dipyrenyl‐ o ‐carborane, 1a , shows dual‐emission from locally excited and intramolecular excimer states. Triple‐fluorescence is achieved for 1b and 1c by introducing a small π‐substituent at the carborane carbon vertices, which allows the formation of a charge‐transfer state that is fluorescent in the near‐infrared (NIR) region tailing to 1200 nm. This work provides a new strategy to activate triple‐fluorescence from a single‐component organic compound, opening a new avenue toward multichannel photonic materials and NIR‑II bioimaging.