Bis(haloBODIPYs) with Labile Helicity: Valuable Simple Organic Molecules That Enable Circularly Polarized Luminescence

125

With our new home-built circularly polarized luminescence (CPL) instrument, we measured fluorescence and CPL spectra of the enantiomeric pairs of two quasi-isomeric BODIPY DYEmers 1 and 2, endowed with axial chirality. The electronic circular dichroism (ECD) and CPL spectra of these atropisomeric dimers are dominated by the exciton coupling between the main π-π* transitions (550-560 nm) of the two BODIPY rings. Compound 1 has strong ECD and CPL spectra (g =4×10 ) well reproduced by TD-DFT and SCS-CC2 (spin-component scaled second-order approximate coupled-cluster) calculations using DFT-optimized ground- and excited-state structures. Compound 2 has weaker ECD and CPL spectra (g =4×10 ), partly due to the mutual cancellation of electric-electric and electric-magnetic exciton couplings, and partly to its conformational freedom. This compound is computationally very challenging. Starting from the optimized excited-state geometries, we predicted the wrong sign for the CPL band of 2 using TD-DFT with the most recommended hybrid and range-separated functionals, whereas SCS-CC2 or a DFT functional with full exact exchange provided the correct sign.

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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

Zinna

Bruhn

Guido

et al. 2016

125

“…However, despite the fact that several BODIPY‐based chiral architectures were found to show significant CPL effects, azabora[ n ]helicenes, that incorporate boron directly in the helical architecture, were reported only in a single work so far . These systems build on borylated arylpyridine N,C‐chelates.…”

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

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.

“…BODIPYs (boron dipyrromethenes; 4‐bora‐3a,4a‐diaza‐ s ‐indacenes) constitute one of the most valuable families of technological dyes . Nowadays, there is a plethora of available synthetic procedures for their direct functionalization, focused on appropriate modulation of key physical (mainly photophysical) properties . These transformations usually involve the BODIPY dipyrrin moiety and well‐established chemical reactions, such as nucleophilic and electrophilic aromatic substitutions, metal‐catalyzed cross‐couplings or enol‐like condensations, among others (blue in Figure ) .…”

Section: Introductionmentioning

confidence: 99%

N‐BODIPYs Come into Play: Smart Dyes for Photonic Materials

Ray

Díaz‐Casado

Avellanal‐Zaballa

et al. 2017

Self Cite

N‐BODIPYs (diaminoboron dipyrromethenes) are unveiled as a new family of BODIPY dyes with huge technological potential. Synthetic access to these systems has been gained through a judicious design focused on stabilizing the involved diaminoboron chelate. Once stabilized, the obtained N‐BODIPYs retain the effective photophysical behavior exhibited by other boron‐substituted BODIPYs, such as O‐BODIPYs. However, key bonding features of nitrogen compared to those of oxygen (enhanced bond valence and different bond directionality) open up new possibilities for functionalizing BODIPYs, allowing an increase in the number of pendant moieties (from two in O‐BODIPYs, up to four in N‐BODIPYs) near the chromophore and, therefore, greater control of the photophysics. As a proof of concept, the following findings are discussed: (1) the low‐cost and straightforward synthesis of a selected series of N‐BODIPYs; (2) their outstanding photophysical properties compared to those of related effective dyes (excellent emission signatures, including fluorescence in the solid state; notable lasing capacities in the liquid phase and when doped into polymers; improved laser performance compared to the parent F‐BODIPYs); (3) the versatility of the diaminoboron moiety in allowing the generation of multifunctionalized BODIPYs, permitting access to both symmetric and asymmetric dyes; (4) the capability of such versatility to finely modulate the dye photophysics towards different photonic applications, from lasing to chemosensing.