Transient Absorption Spectroscopy Probes Ultrafast Excited-State Dynamics in D-π-D Chalcone Derivatives

Chalcone-based π-conjugated systems have attracted significant attention due to their tunable electronic properties and well-defined structure-property relationships. In this work, we have designed, synthesized, and characterized three D-π-D chalcone derivatives, IITR-9, IITR-10, and IITR-11, by incorporating different electron-donating groups, such as triphenylamine and carbazole, at the periphery of the chalcone backbone. The excited state dynamics of these molecules were investigated using femtosecond transient absorption spectroscopy (TAS). It was found that IITR-9, IITR-10, and IITR-11 exhibit an intramolecular charge-transfer (ICT) state, consistent with the solvatochromic behavior and theoretical calculations. TAS results demonstrate that the symmetric derivatives, IITR-9 and IITR-10, which have the same donor group on both sides of the chalcone framework, exhibit a long-lived excited-state absorption band that persists beyond the experimental time window of ~8 ns, suggesting triplet-state formation. However, the asymmetric derivative IITR-11, which consists of electron-donating groups of different strengths, exhibits radiative relaxation from the ICT state with a timescale of 3.0  ±  0.2 ns. These findings demonstrate that the nature of the electron-donating group critically governs the excited-state pathways in chalcone derivatives, including CT and triplet state formation, highlighting its potential for designing optoelectronic applications.