Simple 3,6-disubstituted Carbazoles as Potential Hole Transport Materials: Photophysical, Electrochemical and Theoretical Studies.

Developing effective and low-cost organic hole-transporting materials (HTMs) is crucial for the construction of high-performance perovskite solar cells (PSCs) and to promote their production in commercial ventures. In this context, we herein report the molecular design, synthesis and characterization of two novel D-A-D-A-D architectured 9-(2-ethylhexyl)-9H-carbazoles, connecting the mono/dimethoxyphenyl substituted cyanovinylene sidearms symmetrically at 3rd and 6th positions of the carbazole heterocycle (CZ1-2 ), as potential hole-transporting materials (HTMs). The current work highlights their structural, photophysical, thermal, electrochemical and theoretical investigations, including their structure-property correlation studies. Evidently, the optical studies showcased their excellent fluorescence ability due to their push-pull natured structure with extended π-conjugation. Further, in-depth solvatochromic studies demonstrated their intramolecular charge-transfer (ICT)-dominated optoelectronic behavior, supported by various correlation studies. Also, the optical results revealed that CZ1  and CZ2 display λabs  and λemi  in the order of 410-430 nm and 530-560 nm, respectively, with a bandgap in the range of 2.5-2.6 eV. Finally, their quantum chemical simulations have provided an insight into the predictions of their structural, molecular, electronic and optical parameters. Conclusively, the study furnishes a deeper understanding of the intricacies involved in the structural modification of carbazole-based HTMs for achieving better performance.