Escalating Control over Excited-State Structural Evolution of N,N′-Diphenyl-dihydrodibenzo[a,c]phenazine through the “Rigid-Flexible Coupled” Macrocyclization

Herein, we demonstrate the progressive excited-state structural evolution of a flexible polycyclic π-skeleton by introducing a "rigid-flexible coupling" macrocyclization strategy to impose an ever-escalating constraint. Here, a series of compounds DPAC-RFn (n = 3, 5, 8, 9, 10, 11, 12, 15, 17) were prepared by cyclizing the molecule N,N′-diphenyl-dihydrodibenzo[a,c]-phenazine (DPAC) with a "rigid-flexible coupled" chain composed of a rigid phenyl ring and flexible alkyl chains of varying lengths. Although the absorption remains unchanged (around 350 nm), their emissions exhibit significant chain-length dependence. Nanosecond time-resolved measurements and theoretical calculation confirm the excited-state structural evolution of DPAC-RFn from bend–planar–twist conformers, correlating with successive emission distributions in the blue-green region (n = 3, 5, 8, 9, 470–500 nm), yellow-green region (n = 10, 11, 520–530 nm), and orange-red region (n = 12, 15, 17, 590–620 nm). This study explicitly reveals the excited-state structural diversity of flexible polycyclic π-skeleton derivatives and achieves a large-scale coverage in the emission colors, thereby implying the potential prospects for fundamental studies and practical applications.