The synthesis of boron difluoride complexes of as eries of curcuminoidd erivatives containing various donor end groups is described. Time-dependent (TD)-DFT calculations confirm the charge-transfer character of the second lowest-energy transition band and ascribe the lowest energy band to a" cyanine-like" transition. Photophysical studies reveal that tuning the donors trengtho ft he end groups allows coveringab road spectral range, from the visible to the NIR region, of the UV-visible absorptiona nd fluorescence spectra.T wo-photon-excited fluorescence and Z-scan techniques prove that an increase in the donor strengtho r in the rigidity of the backboner esultsi naconsiderable increase in the two-photon cross section, reaching 5000 GM, with predominant two-photona bsorption from the S 0 -S 2 charge-transfer transition. Direct comparisons with the hemicurcuminoid derivatives show that the two-photon active band for the curcuminoid derivatives has the same intramolecular charge-transfer character and therefore arises from ad ipolar structure. Overall,t his structure-relationship study allowst he optimization of the two-photon brightness (i.e., 400-900GM) with one dye that emits in the NIR region of the spectrum.I na ddition, these dyes demonstrate high intracellularu ptakee fficiencyi nC os7 cells with emission in the visible region, which is further improved by using porous silican anoparticles as dye vehicles for the imaging of two mammalian carcinomac ells type based on NIR fluorescence emission.

The design of novel stimuli-responsive supramolecular systems based on host− guest chemistry implies a thorough understanding of the noncovalent interactions involved. In this regard, some computational tools enabling the extraction of the noncovalent signatures from local descriptors based on the electron density have been previously proposed. Although very useful to detect the existence of such interactions, these analyses provide only a semi-quantitative description, which represents a limitation. In this work, we present a novel computational tool based on the local atomic descriptor IGM-δg inter/At , which is able to decompose the fragment interaction into atomic contributions. Then, the role played by each atom in the formation of the host−guest assembly is quantified by an integrated Δg inter/At score. Herein, we apply the IGM-Δg inter/At approach to some challenging systems, including multimetallic arrays, buckycatchers, and organic assemblies. These systems exhibit unique structural features that make it difficult to determine the host/guest atoms that contribute the most to the guest encapsulation. Here, the Δg inter/At score proves to be an appealing tool to shed light on the guest accommodation on a per-atom basis and could be useful in the rational design of more selective target agents. We strongly believe that this novel approach will be useful for experimental teams devoted to the synthesis of supramolecular systems based on host−guest chemistry.