Vectorial Photoinduced Energy Transfer Between Boron–Dipyrromethene (Bodipy) Chromophores Across a Fluorene Bridge

Abstract

A series of novel multichromophoric, luminescent compounds has been prepared, and their absorption spectra, luminescence properties (both at 77 K in rigid matrix and at 298 K in fluid solution), and photoinduced intercomponent energy-transfer processes have been studied. The series contains two new multichromophoric systems 1 and 2, each one containing two different boron-dipyrromethene (Bodipy) subunits and one bridging fluorene species, and two fluorene-Bodipy bichromophoric species, 6 and 7. Three monochromophoric compounds, 3, 4, and 5, used as precursors in the synthetic process, were also fully characterized. The absorption spectra of the multichromophoric compounds are roughly the summation of the absorption spectra of their individual components, thus demonstrating the supramolecular nature of the assemblies. Luminescence studies show that quantitative energy transfer occurs in 6 and 7 from the fluorene chromophore to the Bodipy dyes. Luminescence studies, complemented by transient-absorption spectroscopy studies, also indicate that efficient inter-Bodipy energy transfer across the rigid fluorene spacer takes place in 1 and 2, with rate constants, evaluated by several experimental methods, between 2.0 and 7.0 x 10(9) s(-1). Such an inter-Bodipy energy transfer appears to be governed by the Förster mechanism. By taking advantage of the presence of various protonable sites in the substituents of the lower-energy Bodipy subunit of 1 and 2, the effect of protonation on the energy-transfer rates has also been investigated. The results suggest that control of energy-transfer rate and efficiency of inter-Bodipy energy transfer in this type of systems can be achieved by an external, reversible input.

4,4′-Difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) as components of novel light active materials

“…109 The laser efficiency was determined to be as high as 18%, but varied depending on the solvent used. This styryl-BODIPY (68) was also bound in a polymer matrix and laser activity was still observed. Ethyl acetate was found to produce the highest laser efficiencies, so poly(methyl methacrylate) (PMMA) polymers were chosen, as MMA mimics the ethyl acetate solvent.…”

“…28). 68,69 In both the fluorene and truxene arrays, efficient energy transfer occurs from one BODIPY to the other. The fluorene was calculated to display almost quantitative energy transfer to the BODIPY, and energy transfer from the donor BODIPY to the acceptor BODIPY was calculated to have an efficiency of >90%.…”

Supramolecular tuning of energy transfer efficiency and direction in a bis(styryl) dye–crown ether conjugate

“…For example, such switching has been realized by changing the complexed metal cations in homo and heterodimers of metalloporphyrins [7], metallocyclodextrin assemblies [8] and [2] ca tenates incorporating the [Ru(tpy) 2 ] 2+ fragment [9]. The control of the FRET direction can be also accomplished by protonation/deprotonation of the donor or acceptor unit as has been shown for oligophenylene vinylene (OPV) phenanthroline [10] and OPV fullerene [11] dyads and for multichromophoric BODIPY systems [12,13]. In addition, sev eral intriguing examples of switchable FRET directions have been re ported that use site specific solvent effects [14], temperature changes [15] or the electronic difference between cation binding sites [16,17].…”

Energy transfer in supramolecular materials for new applications in photonics and electronics

“…Controlling the directionality of multistep energy transfer processes within a single architecture remains a challenge. Recent work by Puntoriero et al 80,81 in BODIPY assemblies provides an elegant example of ultrafast vectorial energy transfer that occurs on the picosecond time scale. Polysaccharides 82 and porous silicate frameworks 83,84 may yet prove to be abundant sources of multivalent scaffolds, which bind chromophores for the construction of light-harvesting architectures.…”