Insights Into Intramolecular Charge Transfer in a Benzoxazole‐Substituted TAPP Derivative: Solvent Effects and DFT Analysis

ABSTRACT In this study, synthesis, characterization, photophysical properties, and DFT calculations of a new tetraaryl‐1,4‐dihydropyrrolo[3,2‐b]pyrrole (TAPP) derivative molecule of A‐π‐D‐π‐A type containing benzoxazole as an acceptor group at 1,4‐positions have been carried out. The target A‐D‐A type molecule was synthesized using 4‐(benzo[d]oxazol‐2‐yl)aniline by the method known in the literature, and it was aimed to obtain the classical TAPP structure in an iron‐catalyzed environment. No product was obtained with the first method; therefore, the reaction conditions were optimized. The reaction time and temperature were varied in a controlled manner; the optimum conditions were determined with a reaction time of 7 h at 60°C. The photophysical behavior of the synthesized benzoxazole‐substituted TAPP derivative was investigated by UV–vis and fluorescence spectroscopy depending on different solvent polarities. In the absorption spectra, the maximum absorption band observed around 330 nm in low polarity solvents shifted to 340 nm in polar solvents. Similarly, fluorescence emissions systematically red‐shifted from hexane to DCM (470–550 nm), and quantum yields decreased significantly (0.41 in hexane and 0.03 in DCM). This bathochromic shift and decrease in intensity indicate that the molecule has high polarity in the excited state whereas the intrinsic charge transfer (ICT) and twisted ICT (TICT) states stabilize with increasing solvent polarity. At the same time, nonluminescent transition channels such as loss of planarity, oxygen‐induced quenching, and internal conversion in the solvent‐excited state also decrease the fluorescence intensity. The findings reveal that this TAPP derivative forms a strong donor‐acceptor system and exhibits high sensitivity to solvent environment.