Chiral microneedles from an achiral bis(boron dipyrromethene): spontaneous mirror symmetry breaking leading to a promising photoluminescent organic material

Supramolecular self-assembly of a highly flexible and achiral meso bis(boron dipyrromethene) [bis-(BODIPY)] dye straightforwardly yields fluorescent micro-fibers, exhibiting an intriguing anisotropic photonic behavior. This performance includes the generation of chiroptical activity owing to spontaneous mirror symmetry breaking (SMSB). Repetition of several self-assembly experiments demonstrates that the involved SMSB is not stochastic but quasi deterministic in the direction of the induced chiral asymmetry. The origin of these intriguing (chiro)photonic properties is revealed by fluorescent microspectroscopy studies of individual micrometric objects, combined with X-ray diffraction elucidation of microcrystals. Such a study demonstrates that J-like excitonic coupling between bis(BODIPY) units plays a fundamental role in their supramolecular organization, leading to axial chirality. Interestingly, the photonic behavior of the obtained fibers is ruled by inherent nonradiative pathways from the involved push-pull chromophores, and mainly by the complex excitonic interactions induced by their anisotropic supramolecular organization

Circularly Polarized Luminescence by Visible-Light Absorption in a Chiral <i>O-</i>BODIPY Dye: Unprecedented Design of CPL Organic Molecules from Achiral Chromophores

Circularly polarized luminescence (CPL) in simple (small, nonaggregated, nonpolymeric) <i>O-</i>BODIPYs <b>(<i>R</i>)-1</b> and <b>(<i>S</i>)-1</b> by irradiation with visible light is first detected as proof of the ability of a new structural design to achieve CPL from inherently achiral monochromophore systems in simple organic molecules. The measured level of CPL (|<i>g</i>_lum|) in solution falls into the usual range of that obtained from other simple organic molecules (10^–5–10^–2 range), but the latter having more complex architectures since axially chiral chromophores or multichromophore systems are usually required. The new design is based on chirally perturbing the acting achiral chromophore by orthogonally tethering a single axially chiral 1,1′-binaphtyl moiety to it. The latter does not participate as a chromophore in the light-absorption/emission phenomenon. This simple design opens up new perspectives for the future development of new small-sized CPL organic dyes (e.g., those based on other highly luminescent achiral chromophores and/or chirally perturbing moieties), as well as for the improvement of the CPL properties of the organic molecules spanning their use in photonic applications