The dynamically adaptive RVDA materials originate from the delocalized electron distribution across multiple canonical forms, which enables reversible, stimulus-responsive transitions between distinct electronic states. By overcoming a relatively low energy barrier, RVDA molecules undergo reversible interconversion between the neutral state (e.g., N-P=O, N-P=S, N-C=O) and the charged state (e.g., N⁺=P-O^-, N⁺=P-S^-, and N⁺=C-O^-) [Figure 1B]^[23]. This phenomenon has been directly confirmed in single-crystal structures, where the dynamic equilibrium induces significant structural redistributions, characterized by the structural shortening of N-P (or N-C) bonds and the lengthening of P=O (or P=S, C=O) bonds, which imparts partial double- and single-bond characters, respectively^[24]. Furthermore, the insulating nature of the resonance linkage suppresses electronic communication between conjugated moieties, thereby preserving the inherent optical properties of the functional groups while selectively modulating their electrical properties^[25].

RVDA materials at the molecular level lead to remarkably enhanced macroscopic device performance, typically manifesting as stimulus-responsive self-adaptivity^[26]. In practical application scenarios, RVDA molecules enable a reversible transition from the neutral state to the charged state by crossing the energy barrier after being activated by energy sources such as electrical, optical, or thermal energy, thereby unlocking the self-adaptive regulation of multiple optoelectronic properties.

To quantitatively describe resonance interconversion, the resonance variation energy (E_RV) is introduced. E_RV is defined as the energy difference between the most stable neutral state and the charge redistributed state, as shown in Equations (1)-(3):

(1) $$ E_{\mathrm{RV}} =E_{1}-E \\ $$

(2) $$ E_{\mathrm{RV}}^{\prime} =E_{2}-E \\ $$

(3) $$ \Delta E_{\mathrm{RV}} =E_{1}-E_{2} \\ $$

In the above equations, E is the molecular energy of the neutral state, E₁ and E₂ are the energies of two different canonical forms, and ΔE_RV is the energy difference between them.

E_RV plays a decisive role in regulating the molecular resonance interconversion capability^[27], thereby determining the response rate and magnitude of the adaptive variation in macroscopic material properties. A lower E_RV implies a lower energy barrier for resonance variation, facilitating rapid interconversion between neutral and charged resonance states. The resonance variation energy can be effectively tuned by modifying the composition of the resonance linkage. For example, the N-P=S resonance linkage typically exhibits a lower E_RV than N-P=O, due to the weaker back-bonding from sulfur to phosphorus resulting from the longer 3p-2p bond length [Figure 2A]. Notably, extending the number of resonance units enables the development of systems from mono- to di- and even tri-substituted architectures, which exhibit progressively enhanced dynamic self-adaptivity and improved optoelectronic properties [Figure 2B]. More importantly, integrating resonance units with other functional groups enables more complex multifunctional synergistic modulation.

Introducing the RVDA molecule as the host material for OLEDs can achieve balanced bipolar transport. Crucially, the dynamic transition from the neutral to the charged canonical form redistributes the electron density across the molecular framework; while the neutral state governs traditional hole transport, the emergence of the polarized, charged state facilitates efficient electron injection, thereby achieving continuous and balanced migration of both carriers.

For instance, compared to the monosubstituted RVDA derivatives (NDPhPO and NCzPO), the enantiotropic N-P=O resonances in DNCzPO and DNDPhPO significantly enhance electron transport from the polarized carbazole or diphenylamine groups, leading to superior device performance [Figure 3A]^[28]. For the N-P=S system, DNCzPS exhibits a significantly reduced E_RV of 0.72 eV, which leads to a lower barrier for self-adaptive interconversion, thereby achieving more balanced and efficient carrier transport performance [Figure 3B]^[27]. The N-C=O-based DCzCO exhibits an even lower resonance variation energy of 0.40 eV, rendering the resonance variation nearly barrier-free. The carbazole units thereby efficiently transport both holes and electrons, realizing bipolar transport and boosting the EQE of blue PhOLEDs to 31.2% [Figure 3C and D]^[21]. These findings demonstrate that resonance variation promotes efficient and balanced carrier transport, thereby significantly enhancing the macroscopic electroluminescence performance of OLEDs.

RVDA hole-transport materials (HTMs) dynamically reduce interfacial defects and enhance charge transport via resonance interconversion. ^[29]. In response to undercoordinated Pb²⁺ ions, RVDA molecules undergo resonance interconversion to form strong coordination bonds, thereby enabling in situ passivation of interfacial defects and promoting perovskite crystallization. Moreover, owing to the D-R-D or D-R-A architectures essential for constructing RVDA molecules, the strong donor-acceptor (D-A) interactions combined with extensive conjugation facilitate efficient electron delocalization, facilitating efficient hole extraction and rapid charge transport [Figure 4A and B].

Initially, the N-P=O based RVDA molecule CzPFO was employed as HTM, achieving a power conversion efficiency (PCE) of 21.9%^[29]. Subsequently, the N-C=O based CzCOPXZ and NPP, featuring a lower resonance energy, enabled faster resonance interconversion and stronger Pb-O interactions^[30,31]. Large-area devices (1.02 cm²) based on CzCOPXZ reached a PCE of 21.0% and retained 97.4% of their initial efficiency after 1,300 h of continuous 1-sun illumination at 65 °C [Figure 4C and D]. These advances demonstrate that resonance interconversion is highly effective for passivating interfacial defects and enhancing carrier extraction efficiency, which is crucial for improving film quality and enabling the fabrication of large-area inverted PSCs, thereby ensuring both high PCE and long-term stability.