Cross-Conjugated Cruciform Fluorophores

摘要

Inn optoelectronic devices, chromophores can be designednat the molecular level to create materials with proper-nties desired for advanced applications. Organic fluoro-nphores in particular can be constructed with macroscopicnproperties that arise from two distinct contributions: (i) thencollective impact of the molecular backbone and substit-nuents and (ii) the connectivity within the molecule (that is,nthe spatial molecular architecture). Accordingly, the explo-nration of novel conjugated architectures is a productivenarea of current research.nDifferent two-dimensional, “X-shaped” conjugatednmaterials have been synthesized for a variety of applica-ntions. They include spiro compounds, paracyclophanes,nswivel-type dimers, bisoxazole-derived cruciforms, tetra-nethynylethenes, and tetrasubstituted tolanes. A subset ofnthese compounds are constructed from two “perpendicu-nlar” π-conjugated linear arms connected through a cen-ntral aromatic core; examples of these include tetrakis(arylethynyl)benzenes, tetrakis(styryl)benzenes, and tetrasubstitutednthiophenes.nIn this Account, we evaluate 1,4-distyryl-2,5-bis(arylethynyl)benzenes or cruciforms (XFs). Electronic substitution ofnthis “X-shaped” cross-conjugated scaffold tunes both the energy levels of the frontier molecular orbitals (FMOs) andntheir spatial distribution in XFs. The resulting fluorophores exhibit FMO separation, imbuing XFs with unusual yet desir-nable properties for sensory applications.nUsing model analytes, we examine how the underlying FMO arrangement and the nature of analyte interaction elicitnobservable responses. These studies provide a foundation for accessing functional responsive ratiometric cores, demon-nstrating the importance and unique potential of FMO-separated fluorophores.nWe also highlight the essential contribution of serendipity in materials development. Moving beyond one-dimensional molec-nular wire-type fluorophores to two-dimensional “X-shaped” materials provides access to materials with unexpected and excitingnproperties. XFs represent such novel conjugated architectures, and their successful development has frequently has hinged on inspi-nration from structural components and principles developed in diverse research areas.