Substituent-Position-Controlled Electropolymerization Pathways of Indolocarbazole Derivatives for Dissolution-Resistant Organic Cathodes

Abstract Controlling in situ electropolymerization (EP) represents an effective strategy for suppressing dissolution and thereby improving the cycling stability of organic cathodes for secondary batteries. Here, we demonstrate that the substitution position of vinyl groups critically governs EP pathways, thereby determining polymer growth behavior, solubility, and electrochemical stability. Three indolocarbazole derivatives featuring different N-substituents—ICP (phenyl), ICPVM (meta-vinylphenyl), and ICPVP (para-vinylphenyl)—were systematically investigated. ICPVP undergoes efficient EP to form insoluble interconnected polymeric structures, whereas ICP exhibits no detectable EP behavior and ICPVM shows limited and condition-dependent EP, producing short oligomeric species that remain partially soluble. Mechanistic investigations combining spin-density calculations and structural analyses of electropolymerized products reveal that electrochemical oxidation generates N-centered radicals and that radical delocalization toward the vinyl group strongly depends on substituent position. In particular, para-vinyl substitution promotes effective radical localization on the vinyl moiety upon oxidation, enabling efficient intermolecular coupling and network formation, whereas the meta-substituted analogue exhibits less selective radical distribution and limited polymer growth. These distinct EP pathways result in markedly different solubility and morphological evolution during electrochemical cycling. Consequently, ICPVP exhibits stable cycling behavior without capacity decay over 200 cycles, whereas ICP and ICPVM undergo progressive capacity fading due to active-material dissolution. These findings establish substituent-position engineering as an effective molecular strategy that controls EP pathways to enable dissolution-resistant organic electrodes.