1:1 molar mixtures of electron rich dialkoxynapthalene (Dan) and electron deficient 1,4,5,8-napthalenetetracarboxylic diimide (Ndi) derivatives form highly tunable, columnar mesophases with a dark red color due to a charge transfer absorbance derived from alternating face-centered stacking. Certain Dan-Ndi mixtures undergo a dramatic color change from dark red to an almost colorless material upon crystallizing from the mesophase. Macroscopic morphology of the solid is not changed during this process. In order to investigate the origins of this interesting thermochromic behavior, Dan and Ndi side chains were systematically altered and their 1:1 mixtures studied. We have previously speculated that the presence or absence of steric interactions due to side chain branching on the aromatic units controlled the level of color change associated with crystallization. Results from the present study further refine this conclusion including a key crystal structure that provides a structural rationale for the observed results.

Conjugated donor−acceptor copolymers comprised of electron-deficient 1,4,5,8-naphthalenetetracarboxylic diimide (NDI) linked to a series of relatively electron-rich aromatics via ethynyl spacers were synthesized and characterized. While LUMO levels remained constant at −3.75 eV, HOMO levels were sensitive to the relatively electron-rich aromatic donors and systematically tuned from −5.68 to −5.17 eV. Regardless of the electron-rich comonomer, fluorescence and X-ray diffraction data were consistent with the polymer chains being assembled through the stacking of NDI moieties in an offset face-to-face fashion rather than alternating donor−acceptor stacks.

In order to exploit the use of favorable electrostatic interactions between aromatic units in directing the assembly of donor-acceptor (D-A) dyads, the present work examines the ability of conjugated aromatic D-A dyads with symmetric side chains to exhibit solid-state polymorphism as a function of time during the solid formation process. Four such dyads were synthesized and their packing in the solid-state from either slower (10-20 days) or faster (1-2 days) evaporation from solvent was investigated using single crystal X-ray analysis and powder X-ray diffraction. Two of the dyads exhibited tail-to-tail (A-A) packing upon slower evaporation from solvent and head-to-tail (D-A) packing upon faster evaporation from solvent. A combination of single crystal analysis and XRD patterns were used to create models wherein a packing model for the other two dyads is proposed. Our findings suggest that while side chain interactions in asymmetric aromatic dyads can play an important role in enforcing segregated D-A dyad assembly, slowly evaporating symmetrically substituted aromatic dyads allows for favorable electrostatic interactions between the aromatic moieties to facilitate the organization of the dyads in the solid-state.

The unique feature of a two-step ex situ hydropyrolysis vapor upgrading process for producing infrastructure-compatible cellulosic biofuels has been demonstrated for the first time using a double fluidized-bed reactor system.