Two π‐Electrons Make the Difference: From BODIPY to BODIIM Switchable Fluorescent Dyes

Abstract

aza-)BODIPY dyes (boron dipyrromethene dyes) are well-established fluorophores due to their large quantum yields, stability, and diversity,which led to promising applications including imagingt echniques, sensors, organic (opto)electronic materials, or biomedical applications. Although the control of the optical properties in (aza-)BODIPY dyes by peripheral functional groups is well studied, we herein present an ovel approach to modify the 12 p-electron core of the dipyrromethene scaffold.T he replacemento ft wo carbon atoms in the b-positiono faBODIPYd ye by two nitrogen atoms affordeda14 p-electron system, which was termed BODIIM( boron diimidazolylmethene)i ns ystematic analogyt ot he BODIPYd yes. Remarkably,t he BODIIM dye was obtained with aB H 2 -rigidifying entity,w hich is currently elusive and highly sought after for the BODIPY dye class. DFT-Calculations confirmt he [12+ +2] p-electron relationship between BODIPY and BODIIM and reveal as trong shapec orrelationbetween LUMO in the BODIPY and the HOMO of the BODIIM.The modification of the p-system leads to ad ramatic shifto ft he optical properties, of whicht he fluorescent emissioni smost noteworthy and occurs at much larger Stokess hift, that is, % 500 cm À1 in BODIPY versus > 4170 cm À1 in BODIIM system in all solvents investigated. Nucleophilic reactivity was found at the meso-carbona tom in the formation of stable borane adducts with as ignificant shift of the fluorescent emission, and this behavior contrasts the reactivity of conventional BODIPY systems. In addition, the reversedecomplexation of the borane adducts was demonstrated in reactions with ar epresentative N-heterocyclic carbene to retain the strongly fluorescent BODIIM compound, which suggestsa pplications as fully reversible fluorescent switch.

BODIPY-Pyridylhydrazone Probe for Fluorescence Turn-On Detection of Fe3+ and Its Bioimaging Application

“…The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of BODIPY-PH and BODIPY-PH-Fe 3+ complex with the isovalue of 0.02 and their corresponding energy gaps are illustrated in Figure 12A. The density distributions of HOMO-and LUMO-electrons on the BODIPY-PH are mainly located on the BODIPY backbone as also observed in other BODIPY derivatives according to the literature [62][63][64]. In addition, there are no π-electrons covered on the pyridylhydrazone moiety which indicates the separation of the π-conjugated system on the BODIPY core from the one on pyridylhydrazone unit.…”

Validation of Local Hybrid Functionals for Excited States: Structures, Fluorescence, Phosphorescence, and Vibronic Spectra

“…Due to its favorable cost-performance ratio, linear-response time-dependent density functional theory (TDDFT) is currently the most popular quantum-chemical approach to study photochemical and photophysical processes of mediumsized to large molecular systems. 1 Typical applications are the prediction of absorption and emission spectra, 2 simulation of photoinduced reactions, 3 prediction of photophysical properties, 4,5 or large-scale screenings of chromophores. 6 The reliability of such calculations depends strongly on the choice of the exchange-correlation (XC) functional and the associated potential and kernel.…”

Boron bis-(4-methylbenzoxazol-2-yl)-methanide complexes

“…The B–N bond lengths ( d (B1–N1) = 1.5770(18) Å, d (B1–N2) = 1.5824(18) Å) are slightly longer than those in BODIIM (boron diimidazolylmethene) (1.546(1) and 1.550(1)) that were published before. 15 The C 3 N 2 unit in [ 4-Me Box–BH 2 ] ( 1 ) shows bond lengths of 1.3883(2) Å (C7–C8) and 1.3901(19) Å (C8–C9) and of 1.3373(2) Å (N1–C7) and 1.3381(2) Å (N2–C9). Interestingly, the planar molecule reveals crystallographic m symmetry and thus, neither a dislocation of the boron atom from the C 3 N 2 moiety nor a butterfly folding between both benzoxazyl moieties is observed as in many other bis-(benzoxazol-2-yl)-methanide complexes.…”