Circularly Polarized Luminescence from Axially Chiral BODIPY DYEmers: An Experimental and Computational Study

Three helicenes based on a borylated arylisoquinoline skeleton have been prepared in their enantiopure forms and characterized with respect to their photophysical properties, including the use of chiroptical spectroscopies. The dyes show varying charge-transfer characteristics and efficient emission (quantum yields between 0.13 and 0.30, in toluene), which is governed by the electron-donor substitution (p-MeO-phenyl, p-Me N-phenyl) at the helicene. Marked differences in the emission wavelength and Stokes shift are observed, with the dimethylamino-substituted derivative emitting most red-shifted (maximum at ca. 590 nm) and displaying the highest Stokes shift (ca. 6000 cm ) in toluene. The helicenes show electronic circular dichroism (ECD) and significant circularly polarized luminescence (CPL) with dissymmetry factors of up to 3.5×10 . The sign of the ECD band corresponding to the first transition and of the CPL spectrum depend sensibly on the electron-donor substitution.

Section: Introductionmentioning

confidence: 99%

Azabora[5]helicene Charge‐Transfer Dyes Show Efficient and Spectrally Variable Circularly Polarized Luminescence

Domínguez

López‐Rodríguez

Álvarez

et al. 2018

“…This shift led to a significant increase in the Stokes shift, from λ =475 cm −1 in 3 a [or diastereomer ( R , S )‐ 2 a ] to up to λ =1460 cm −1 for chiral dimer ( R , R )‐ 2 a . This value even surpasses those observed for purposely designed energy‐transfer cassettes and reaches those of related BODIPY dimers . These features are indicative of a geometrical rearrangement upon excitation, which boosts energy‐relaxation processes, and this leads to both a loss in fluorescence efficiency ( φ =0.33) and a significant decrease in the fluorescence lifetime.…”

Section: Resultsmentioning

confidence: 69%

Stereochemical and Steric Control of Photophysical and Chiroptical Properties in Bichromophoric Systems

Blázquez-Moraleja

Cerdán

García‐Moreno

et al. 2018

Stereochemical and steric control of the relative spatial arrangement of the chromophoric units in multichromophoric systems offers an interesting strategy for raising unusual and appealing light-induced emission states. To explore and exploit this strategy, a series of conformationally restricted boron-dipyrromethene (BODIPY) dimers were designed by using tartaric acid as a symmetrical connector between the boron atoms of the dyes. The variety of stereoisomeric forms available for this bis(hydroxy acid) allows the relative spatial orientation of the chromophoric units in the dimer to be modified, which thus opens the door to modulation of the photophysical and chiroptical properties of the new bichromophoric systems. Chromophore alkylation introduces an additional level of control through distance-dependent steric interactions between the BODIPY units in the dimer, which also modulates their relative spatial disposition and properties.

“…As expected, the absorption spectrum of Zn(Phena‐dpm) 2 (Figure A, spectrum a) was redshifted and broadened relative to that of free Phena‐dpm‐H (Figure A, spectrum b). More importantly, the original absorption maximum at 522 nm was found as split peaks for the helicate at 548 and 615 nm, due to excitonic coupling . A forbidden peak at 575 nm for Zn(Phena‐dpm) 2 (among the couplet) is assigned as distinct transition originating from the distorted geometry (Figures S10 and S11 in the Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

Significant Enhancement of Absorption and Luminescence Dissymmetry Factors in the Far‐Red Region: A Zinc(II) Homoleptic Helicate Formed by a Pair of Achiral Dipyrromethene Ligands

Ito

Sakai

Okayasu

et al. 2018

A homoleptic zinc(II) helicate organized by a pair of achiral dipyrromethene ligands through zinc(II) coordination was synthesized to evaluate the chiroptical properties. This zinc complex showed strong exciton-coupled chiroptical responses from the helical configuration with a large absorption dissymmetry factor |g | (up to 0.20). More importantly, intense polarized luminescence in the far-red region (700-850 nm) with a fluorescence quantum yield Φ of 0.23 was observed for this helicate with a dissymmetry factor |g | of 0.022, the largest value among rare-earth- and precious-metal-free small molecules. These unprecedentedly large g values were supported by theoretical calculations.