N -Heteroaromatic Fused BODIPY Dimers: Ring-Size Effects from Five- to Six-Membered Rings

Three BODIPY dimers fused with five- and six-membered N-heterocycles were synthesized via an S_NAr and C-H activation strategy. N-Heterocycle size enables precise modulation of electronic delocalization and excited-state character. The six-membered fused PP-di exhibits panchromatic absorption, a narrowed HOMO-LUMO gap, and enhanced intramolecular charge-transfer behavior, whereas the five-membered analogues Cl-PL-di and PL-di display predominantly localized-excited states.