Herein, a full investigation of the optical properties and first-principles calculations of a large series of original 2-(2'-hydroxybenzofuran)benzazole (HBBX) dyes is described. The electronic substitution on the π-conjugated core of the fluorophores and the nature of the heteroatom (O, S, N) was varied extensively to assess the necessary parameters to trigger a partial frustration of the excited-state intramolecular proton transfer (ESIPT) process, which results in the emission of both tautomers, that is, enol and keto (E* and K*). The optical properties, studied in solution and in the solid state, revealed the appearance of either an intense single K* or a dual E*/K* emission; a feature that is highly dependent on the electronic substitution (donating or accepting), the heteroelement, and the close environment. Subtle modifications of these parameters allowed the establishment of structure-property relationships that were successfully rationalized by first-principles calculations. In particular, the E*/K* emission intensity ratio was shown to be directly related to the free energies of the two emissive tautomers in the excited state.

Both symmetrical and unsymmetrical α-fused dithienyl-BODIPY dyes have been prepared by oxidative ring closure induced by anhydrous FeCl3. Extension of the π-system in the fused BODIPY leads to a progressive shift to 579 and 665 nm respectively for the absorption wavelength maxima of the mono- and difused dyes relative to the unfused species (λ(abs) = 502 nm). Linking such dyes to an NIR emitting module provides a panchromatic chromophore with a large absorption cross section in the visible range associated with efficient intramolecular cascade energy transfer.

The preparation of highly water-soluble and strongly fluorescent diketopyrrolopyrrole (DPP) dyes using an unusual taurine-like sulfonated linker has been achieved. Exchanging a phenyl for a thienyl substituent shifts the emission wavelength to near λ=600 nm. The free carboxylic acid group present in these new derivatives was readily activated and the dyes were subsequently covalently linked to a model protein (bovine serum albumin; BSA). The bioconjugates were characterized by electronic absorption, fluorescence spectroscopy and MALDI-TOF mass spectrometry, thus enabling precise determination of the labeling density (ratio DPP/BSA about 3 to 8). Outstanding values of fluorescence quantum yield (30% to 59%) for these bioconjugates are obtained. The photostability of these DPP dyes is considerably greater than that of fluorescein under the same irradiation conditions. Remarkably low detection limits between 80 and 300 molecules/μm(2) were found for the BSA bioconjugates by fluorescence imaging with a epifluorescence microscope.

Formation of radical–radical cocrystals is an important step towards the design of organic ferrimagnets. We describe a simple approach to generate radical–radical cocrystals through the identification and implementation of well‐defined supramolecular synthons which favor cocrystallization over phase separation. In the current paper we implement the structure‐directing interactions of the E−E bond (E=S, Se) of dithiadiazolyl (DTDA) and diselenadiazolyl (DSDA) radicals to form close contacts to electronegative groups. This is exemplified through the preparation and structural characterization of three sets of radical cocrystals; the 2:2 cocrystal [PhCNSSN]2[MBDTA]2 (4) [MBDTA=methyl benzodithiazolyl] and the 2:1 cocrystals [C6F5CNEEN]2[TEMPO] (E=S, 5; E=Se, 6). In 4 the two types of radical are linked via bifurcated inter‐dimer δ+S⋅⋅⋅Nδ− interactions whereas 5 and 6 exhibit a set of five‐centre δ+E⋅⋅⋅Oδ− contacts (E=S, Se).

The ability of an unconstrained boron dipyrromethene dye to report on changes in local viscosity is improved by appending a single aryl ring at the lower rim of the dipyrrin core. Recovering the symmetry by attaching an identical aryl ring on the opposite side of the lower rim greatly diminishes the sensory activity, as does blocking rotation of the meso-aryl group. On the basis of viscosity- and temperature-dependence studies, together with quantum chemical calculations, it is proposed that a single aryl ring at the 3-position extends the molecular surface area that undergoes structural distortion during internal rotation. The substitution pattern at the lower rim also affects the harmonic frequencies at the bottom of the potential well and at the top of the barrier. These effects can be correlated with the separation of the H1,H7 hydrogen atoms.

The preparation and characterization of the halo-functionalized dithiadiazolyl radicals p-XC 6 F 4 CNSSN (X = Br (1) or I (2)) are described. Compound 1 is trimorphic. The previously reported phase 1α (Z′ = 1) comprises monomeric radicals, whereas 1β comprises a mixture of one cis-oid π*−π* dimer and one monomer (Z′ = 3), and 1γ exhibits a single cis-oid dimer (Z′ = 2) in the asymmetric unit. We have only been able to isolate a single polymorph of 2, isomorphous with 1α. Both the bromo and iodo groups in 1 and 2 promote sigma-hole type interactions of the type C−X•••N (X = Br, I), reflecting the increasing strength of this interaction for the heavier halo-derivatives. An analysis of the intermolecular forces is made using dispersion corrected density functional theory (DFT) (UM06-2X-D3/LACV3P*) and compared to a unified pair potential model (UNI) embodied in the crystallographic software Mercury. While there is a correlation between DFT and UNI force-field models, there are some discrepancies, although both reveal that a number of intermolecular contacts beyond the sum of the van der Waals radii are significant (>5 kJ mol −1 ). A natural bond order analysis of the intermolecular interactions reveals lone pair donation from the heterocyclic N atom to C−X or S−S σ* orbitals contributes to these intermolecular interactions with relative energies in the order C−I > SN-II > C−Br > SN-III. The magnetism of 2 reveals a broad maximum in χ around 20 K indicative of short-range antiferromagnetic interactions. These are supported by DFT calculations that reveal a set of three significant exchange interactions which propagate in two dimensions.

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Characterization data of selected compounds 2) Complementary steady-state spectra DPP 3) Spectra of differential ε 's 4) Singular Value Decomposition 5) 290fs DADS 6) References 1) Characterization data of selected compounds TPA-DPP-TPA λ max abs (THF) = 623 nm (ε = 83 500 M-1 cm-1); λ max emis (THF) = 660 nm, Φ = 0.32 in THF (the reference used was a reported BODIPY dye (Φ = 0.49 in CH 2 Cl 2 , excitation @650 nm). 1