The amorphous and crystalline f orms of molecular materials, their reversible interconversion and switching of their associated f unctional attributes are of great conceptual and practical interest. Fundamental structure-f unction correlations that provide an understanding of such materials and the associated phase transf ormations are extremely usef ul in developing novel molecular materials-based devices. In the present work, we have synthesized two series of alkoxyalkyl DADQ (ROR′-DADQs) molecules and characterized them in detail including their molecular and crystal structure. Thermal analysis, optical spectroscopic investigations and crystallographic studies of these materials reveal well-def ined trends in the molecular structural f eatures that impact upon the solid -state f orm in terms of amorphous and crystalline structures, and the closely correlated f luorescence emission characteristics. The RO2-DADQs with the shorter R groups and the RO3-DADQs with the longer R groups show a clear tendency towards the amorphous and crystalline states respectively. Signif icantly, the intermediate systems appear to be suited f or the realization of bistable states and hence phase change material applications; a subtle balance in the length of the R and R′ units and the associated chain f lexibility is the key structural f actor. A molecular structurephase correlation diagram that emerges f rom these considerations is schematically represented in Figure . These observations are not only consistent with our earlier discovery of the DADQ based f unctional molecular phase change materials, but allowed us to Please do not adjust margins Please do not adjust margins test and conf irm the predictive capability of the present analysis. The detailed crystallographic structural investigations of these molecules provided signif icant insights into the intramolecular f eatures and intermolecular interactions in the solid state that have a direct bearing on the tendencies towards the amorphous, crystalline or bistable f orms.