Unveiling the Electronic and Optoelectronic Behavior of Phenothiazine Derivatives through Theoretical Insights

High Resolution Image Download MS PowerPoint Slide A series of phenothiazine-based donor–π–acceptor derivatives (PTZ1–PTZ10) were systematically designed and investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) to elucidate structure–property relationships governing their optoelectronic performance. Strategic incorporation of aryl substituents with varying electronic character enables fine-tuning of molecular planarity, Frontier orbital energies and intramolecular charge transfer (ICT). Frontier molecular orbital analysis reveals efficient donor–acceptor separation across the series, with reduced band gaps and enhanced delocalization observed for PTZ6–PTZ10, promoting stronger ICT and improved light-harvesting capability. TD-DFT results indicate pronounced bathochromic shifts and high oscillator strengths for these derivatives, with absorption extending toward the visible region. Solvent-dependent studies further confirm strong solvatochromic behavior, highlighting the stabilization of charge-transfer excited states in polar environments. Excited-state analysis shows small singlet–triplet energy gaps (Δ E ST = 0.155–0.417 eV), suggesting efficient intersystem crossing and exciton utilization. Charge-transport analysis demonstrates that PTZ7 and PTZ10 are favorable for hole transport, while PTZ2 and PTZ5 exhibit superior electron-transport properties, with several derivatives displaying balanced ambipolar characteristics. Notably, PTZ10 exhibits the highest light-harvesting efficiency, favorable injection driving force and strong charge separation, identifying it as the most promising candidate for photovoltaic applications. Complementary NCI-RDG and QTAIM analyses reveal that hydrogen bonding and dispersion interactions play key roles in stabilizing molecular conformations and facilitating electronic communication. Overall, this study provides a comprehensive framework for the rational design of phenothiazine-based chromophores, offering valuable insights for the development of efficient materials for dye-sensitized solar cells and related optoelectronic devices.