Regulating Structures and Properties of Overcrowded-Ethylene Decorated (Diaza)Phosphinines via Tunable Main-Group Element Hyperconjugation

Creating more sophisticated molecular systems that are responsive, dynamic, and controllable through a combination of chemical structure modification and external stimuli represents a pivotal challenge in the development of functional molecular machines. Herein, we report a new series of overcrowded-ethylene (OCE) decorated (diaza)phosphinines. Combining with the main-group element and nonplanar OCE structures, new P-molecules showed the tunable folded(F)/twisted(T)-conformations and physical properties via the distinct P-hyperconjugation of the P─C and P─N bonds. Such hyperconjugation-induced tunability is different from the classical OCEs where p-π/π-π conjugation effects are the dominating factors controlling the structures and properties. Furthermore, bromination of NP-oxide derivative induced an unexpected chemochromic T→F isomerization, highlighting the dynamic conformation character. Leveraging on the different structures, CP and NP derivatives further enabled the formations of radical cations and anions having different spin characters on the P-centers. As the new example of P-Thiele's hydrocarbon family, combining the NP structure with the overcrowded anthraquinodimethane structure yielded a light-responsive open-shell NP-anthraquinodimethane diradicaloid with a triplet ground state, which was influenced by the PN hyperconjugation effect in F-conformation and the aromaticity gain in T-conformation. Overall, our new strategy, namely the hyperconjugation-regulated tunability, paves the way toward complex organic materials with tunable the structures and physical properties.