Donor Engineering Meets Main-Group Organometallic Interplay: Carbazole Versus Anthracene in Cyanostilbene-Borane...

We present a comparative investigation of two main-group organoboron donor-acceptor (D-A) luminophores, carbazole-cyanostilbene-duryl-bridged dimesitylborane (CZ-CS-TAB) and anthracene-cyanostilbene-duryl-bridged dimesitylborane (AN-CS-TAB), to elucidate the influence of donor identity and molecular connectivity on their photophysical behavior in solution as well as solid-state. Both compounds were synthesized via stepwise Knoevenagel condensation followed by Suzuki-Miyaura coupling and characterized comprehensively by multi nuclear NMR, and HRMS spectroscopy. In solution state, CZ-CS-TAB exhibits hybridized local charge transfer (HLCT) excited state with moderate solvatochromism (440-475 nm), while AN-CS-wTAB displays only locally excited (LE) emission with minor solvatochromic response. Both systems demonstrate typical aggregation-induced emission (AIE) and solid-state emissive characteristics, accompanied by mechanochromic fluorescence (MFC) behavior. Mechanical grinding induces a reversible blue-to-cyan shift (460→495 nm→480 nm) in CZ-CS-TAB and a small red shift (530→540→535 nm) in AN-CS-TAB, correlating with a crystalline-to-amorphous transformation confirmed by PXRD. DFT and TD-DFT analyses support the donor-dependent HLCT and LE excited states, rationalizing the observed emission features. Both luminophores exhibit excellent thermal stability (T_d ≈ 350 °C). This study highlights how donor engineering coupled with borane acceptor frameworks enables systematic modulation of emissive, AIE, and mechanochromic properties, offering design strategies for multifunctional main-group organometallic luminophores.