An asymmetric BODIPY triad with panchromatic absorption for high-performance red-edge laser emissionby Gonzalo Duran-Sampedro, Antonia R. Agarrabeitia, Inmaculada Garcia-Moreno, Leire Gartzia-Rivero, Santiago de la Moya, Jorge Bañuelos, Íñigo López-Arbeloa, María J. Ortiz

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ARBELOA and M. J. Ortiz, Chem. Commun., 2015, DOI: 10.1039/C5CC03408F.

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Asymmetric BODIPY triad with panchromatic absorption for highperformance red-edge laser emission†

Gonzalo Duran-Sampedro, a

Antonia R. Agarrabeitia, a

Inmaculada Garcia-Moreno, b

Leire GartziaRivero, c

Santiago de la Moya, a

Jorge Bañuelos,* ,c Íñigo López-Arbeloa, c and María J. Ortiz* ,a

Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X 5

DOI: 10.1039/b000000x

A rational design of an unprecedented asymmetric cassette triad based entirely on BODIPY chromophores allows efficient light harvesting over the UV-vis spectral region, leading to a bright and stable red-edge laser emission via 10 efficient energy-transfer processes.

Long wavelength (>600 nm) fluorescent dyes have found applications in a wide variety of fields, such as laser printing, information storage, displays and solar power conversion.1 They have also proved to be useful tools in biomedical applications 15 (including photodynamic therapies),2 due mainly to the deeper penetration into tissues of this kind of light.3 Although a number of long-wavelength emitting commercial dyes with reasonable efficiency are available,4 these dyes have important drawbacks: low absorption at the standard pump wavelengths (355 and 532 20 nm) and/or poor photostability. One approach to overcome these drawbacks is the straightforward synthesis of energy transfer cassettes,5 which has proved to be a powerful strategy in fields such as light-harvesting systems and sensors.6 Thus, these complex molecular multichromophoric systems offer two main 25 valuable advantages with regard to simpler systems and physical mixtures of individual (non-covalently linked) chromophores: (1) possibility of excellent excitation energy transfer (EET) efficiencies upon absorption over a broad spectral window, to yield almost exclusively the emission of a target chromophore 30 unit; (2) possibility of performing the excitation far away from the emission region, which enhances both the system photostability and the sensibility when detecting the emission signal. However, this approach has not been tried to date to develop panchromatic dyes with enhanced red-edge laser 35 emission.

In this regard, the rational design of a multichromophoric molecular system with the aforementioned EET benefits is challenging, since the effectiveness of each individual EET event depends on the mutual separation and relative orientation of the 40 involved donor and acceptors moieties. BODIPYs (4,4-difluoro4-bora-3a,4a-diaza-s-indacenes) have demonstrated to be valuable scaffolds to design cascade-like EET architectures,7 since they can be properly functionalized to assure strong absorption throughout the visible spectrum.8 On the other hand, 45 high efficiency of monochromatic emission beyond 650 nm can be obtained from certain conveniently-functionalized BODIPYs.9

On the basis of this synthetic versatility of the BODIPY chromophores for designing energy-transfer systems, herein we came to report a straightforward, efficient and cost-effective 50 synthetic protocol to produce an unprecedented panchromatic allBODIPY cassette triad (1 in Fig. 1) enabling highly efficient and stable laser emission at 665 nm.

The asymmetric molecular architecture of 1 is not trivial, at it was judiciously designed to get the desired photophysical 55 property thought to the simpler synthetic route. Thus, its twisted architecture was selected to avoid supramolecular aggregation by - stacking interactions, which are known to have a deleterious effect on laser action. However, compared to symmetric BODIPY systems, which can be straightforwardly synthesized (e.g., from 60 pyrrole derivatives), a facile and scalable synthesis of low symmetric BODIPY analogues is still challenging.

Fig. 1. Developed cassette triad. Key BODIPY moieties in different colours (spacers in black). Individual key synthetic building-block fragments inside dotted windows. 65

The lateral 8-aminoBODIPY moiety of 1 (blue fragment in

Fig. 1) was selected as the short-wavelength donor due to the known strong absorption and highly efficient and stable emission in the blue-green spectral region exhibited by related individual 70

BODIPYs (400-500 nm).10 On the other hand, the central 8mesitylBODIPY moiety (green moiety in Fig. 1) was chosen on the basis of its expected strong absorption and emission in the green-orange spectral region (490-600 nm),11 which should allow the required dual behaviour of the central core inside the triad 75 (donor and acceptor moiety), but also because the corresponding isolated BODIPY results a convenient synthetic building block to let its lateral asymmetric functionalization as shown later. Finally, the 3,5-distyrylBODIPY chromophore (red fragment in Fig. 1) was selected due to its likely strong absorption and high efficient 80