Synthesis, photophysical, electrochemical, and non-linear optical properties of triaryl pyrazole based B-N coordinated boron compounds

We report here a set of triaryl pyrazole based B-N coordinated boron compounds ( 11 - 17 ) synthesized by electrophilic aromatic borylation strategy. All the pyrazole boron compounds were thoroughly characterized using multinuclear NMR spectroscopy, LCMS, and single crystal X-ray diffraction analysis (for 12 - 17 ). The photoluminescence measurements of 11 - 17 revealed that the emission peak maxima were tuned based on the substitution on Nphenyl. The photophysical and electrochemical properties were further supported by theoretical calculations. Z-scan based investigations at 515 nm pump wavelength showed that B-N coordination led to enhancement of nonlinear absorption (two-photon absorption (TPA)) in these compounds if an electron deficient moiety is attached. It has also been observed that an appropriate choice of moiety allows to optimally maneuver the molecular polarizability of the π-system and consequently, assists in controlling the third-order nonlinear optical response.

Functionalization of boron dipyrrin (BODIPY) dyes through iridium and rhodium catalysis: a complementary approach to alpha- and beta-substituted BODIPYs

Iridium-catalyzed direct borylation has been applied to meso-substituted dipyrromethane and boron dipyrrin (BODIPY) dyes. Borylation is highly regioselective and complementary: it occurs exclusively at the alpha position for meso-mesityldipyrromethane and at the beta positions for meso-mesityl BODIPY dye. This regioselective borylation enables a variety of alpha- and beta-substituted BODIPY dyes to be synthesized. Introduction of alpha,beta-enoate and alpha,beta,gamma,delta-dienoate functions into BODIPY dyes at the alpha or beta positions was achieved by rhodium-catalyzed Heck-type addition of the borylated compounds to acrylate and 2,4-pentadienoate esters. This functionalization has a significant effect on the electronic properties of BODIPY dyes, as seen in substantial redshift of the absorption and emission spectra. Comparative studies showed that the alpha- and beta-substituted series of BODIPY dyes show substantially different photophysical properties, and thus the importance of the position to be functionalized is highlighted.

An Ionically Driven Molecular IMPLICATION Gate Operating in Fluorescence Mode

An asymmetrically core-extended boron-dipyrromethene (BDP) dye was equipped with two electron-donating macrocyclic binding units with different metal ion preferences to operate as an ionically driven molecular IMPLICATION gate. A Na(+)-responsive tetraoxa-aza crown ether (R(2)) was integrated into the extended pi system of the BDP chromophore to trigger strong intramolecular charge transfer (ICT(2)) fluorescence and guarantee cation-induced spectral shifts in absorption. A dithia-oxa-aza crown (R(1)) that responds to Ag(+) was attached to the meso position of BDP in an electronically decoupled fashion to independently control a second ICT(1) process of a quenching nature. The bifunctional molecule is designed in such a way that in the absence of both inputs, ICT(1) does not compete with ICT(2) and a high fluorescence output is obtained (In(A)=In(B)=0-->Out=1). Accordingly, binding of only Ag(+) at R(1) (In(A)=1, In(B)=0) as well as complexation of both receptors (In(A)=In(B)=1) also yields Out=1. Only for the case in which Na(+) is bound at R(2) and R(1) is in its free state does quenching occur, which is the distinguishing characteristic for the In(A)=0 and In(B)=1-->Out=0 state that is required for a logic IMPLICATION gate and Boolean operations such as IF-THEN or NOT.

Proton- and Redox-Controlled Switching of Photo- and Electrochemiluminescence in Thiophenyl-Substituted Boron-Dipyrromethene Dyes

A luminescent molecular switch in which the active thiol/disulfide switching element is attached to a meso-phenyl-substituted boron-dipyrromethene (BDP) chromophore as the signalling unit is presented. The combination of these two functional units offers great versatility for multimodal switching of luminescence: 1) deprotonation/protonation of the thiol/thiolate moiety allows the highly fluorescent meso-p-thiophenol-BDP and its nonfluorescent thiolate analogue to be chemically and reversibly interconverted, 2) electrochemical oxidation of the monomeric dyes yields the fluorescent disulfide-bridged bichromophoric dimer, also in a fully reversible process, and 3) besides conventional photoexcitation, the well separated redox potentials of the BDP also allow the excited BDP state to be generated electrochemically (i.e., processes 1) and 2) can be employed to control both photo- and electrochemiluminescence (ECL) of the BDP). The paper introduces and characterizes the various states of the switch and discusses the underlying mechanisms. Investigation of the ortho analogue of the dimer provided insight into potential chromophore-chromophore interactions in such bichromophoric architectures in both the ground and the excited state. Comparison of the optical and redox properties of the two disulfide dimers further revealed structural requirements both for redox switches and for ECL-active molecular ensembles. By employing thiol/disulfide switching chemistry and BDP luminescence features, it was possible to create a prototype molecular ensemble that shows both fully reversible proton- and redox-gated electrochemiluminescence.