Electronic structure and superalkali character of Li-functionalized polycyclic carbon systems

The interplay between π-electron delocalisation and superalkali behaviour in Li-decorated π-conjugated species offers a unique platform for tuning electronic properties. To explore this synergy, a systematic investigation of C6 + 4kLi6 + 2k (k = 0-7) was performed, encompassing species from C6Li6 to C34Li20. The optimised geometries exhibit planar-to-quasi-planar frameworks with consistent Li–C coordination (∼1.9 Å), indicating uniform binding across the series. A steady decrease in vertical ionisation energy (VIE) from 4.48 eV (C6Li6) to 3.12 eV (C34Li20) confirms their pronounced superalkali nature. Electronic-structure analysis shows that Li-induced charge-transfer enhances delocalisation throughout the carbon framework. Aromaticity descriptors (HOMA, NICS, NICSzz, PDI, and PLR) further support this behaviour, indicating that Li substitution modulates but does not disrupt the underlying conjugation. The concurrent reduction in VIE and HOMO–LUMO gap reflects a balance between intrinsic electronic delocalisation and Li-induced charge-transfer. These findings establish Li-decorated polycyclic species as tunable superalkali systems, providing insight into the design of extended π-conjugated superalkali systems.