Crystallochromy and Reversible-Phase Transition in 2,6-Diamino-benzo[1,2-b:4,5-b′]difuran-3,7-diethyl Ester Single Crystals: Experimental and Theoretical Insights

The benzo[1,2-b:4,5-b′]difuran core has emerged as a building block for the development of electronic and optoelectronic compounds, pharmacologically active molecules, and even antiproliferative tools for different cancer cell lines. In our past research articles, we analyzed the properties of a series of diaminobenzo[1,2-b:4,5-b′]difuran derivatives with different substituents, both from the functional and crystallographic points of view. We herein have investigated the effect of different crystallization conditions on 2,6-diamino-benzo[1,2-b:4,5-b′]difuran-3,7-diethyl ester. We both obtained the known colorless crystalline structure 1a(RT) and another violet colored crystal form containing DMF as guest molecules, named 1b. On the other hand, we recorded the ability of 1a(RT) to change into another colorless crystal form named 1a(LT) at 100 K, undergoing a reversible-phase transformation accompanied by a reversible twinning/detwinning process. The solid-state assembly of the three crystal forms was deeply examined; specific absorption curves and colorimetric coordinates were studied, and the energetic characteristics were derived by computational methods.