Near-Infrared Emissive B-N Lewis Pair-Functionalized Anthracenes via Selective LUMO Delocalization in Extended Conjugated Dimer and Polymer: Synthesis, Photophysical Properties, and Effects on Endoperoxide Formation

Acenes are attractive as building blocks for low band gap organic materials with applications, for example, in organic light emitting diodes (OLEDs), solar cells, bioimaging and diagnostics. Previously, we have shown that modification of dipyridylanthracene via B-N Lewis pair fusion (BDPA) strongly redshifts the emission, while facilitating self-sensitized reactivity toward O2 to reversibly generate the corresponding endoperoxides. Here, we report on the further enlargement of the pi-conjugation system of BDPA to a vinyl-substituted monomer, vinylene-bridged dimer, and a high molecular weight polymer with an average of 20 chromophores. We demonstrate that the extension of -conjugation results in further reduced band gaps of 1.8 eV for the dimer and 1.7 eV for the polymer, the latter giving rise to near-infrared (NIR) emission with a maximum at 731 nm and an appreciable quantum yield of 7%. Electrochemical and computational studies reveal efficient delocalization of the lowest unoccupied molecular orbital (LUMO) along the pyridyl-anthracene-pyridyl axis, which results in effective electronic communication between BDPA units, selectively lowers the LUMO energy levels, and ultimately narrows the band gap. Time-resolved emission and transient absorption (TA) measurements offer insights into the pertinent photophysical processes. Extension of -conjugation also slows down the self-sensitized formation of endoperoxides, while significantly accelerating the thermal release of singlet oxygen to regenerate the parent acenes.