Photoswitchable Fluorescent Assemblies Based on Hydrophilic BODIPY−Spiropyran Conjugates

Abstract

In search of strategies to design photoswitchable fluorescent probes and operate them in aqueous environments, we have envisioned the possibility of incorporating fluorescent, photochromic, and hydrophilic components within the same macromolecular construct. First, we synthesized a fluorophore-photochrome dyad, pairing a BODIPY fluorophore and a spiropyran photochrome in its molecular skeleton, and investigated the photochemical and photophysical properties of this compound in acetonitrile. Under these conditions, the photoinduced isomerization of the spiropyran causes a 56% decrease in the emission intensity of the BODIPY at the photostationary state. The photogenerated isomer has a lifetime of 2.7 × 10 2 s and reverts thermally to the original form, restoring the initial emission intensity. On the basis of these results, we copolymerized a similar BODIPY-spiropyran conjugate with a monomer bearing a pendant polyethylene glycol chain. The resulting polymer is soluble in aqueous environments, and its fluorescence can be modulated by operating the photochromic components with optical stimulation. Specifically, the emission intensity decreases by 40% at the photostationary state and reverts to the initial value after thermal reisomerization of the photochromic components. However, the lifetime of the photogenerated species in neutral buffer is significantly longer than that of the monomeric BODIPY-spiropyran in acetonitrile. The fluorescence of both monomeric and polymeric fluorophore-photochrome assemblies can be switched repeatedly between high and low values by alternating ultraviolet irradiation and storage in the dark. However, the fatigue resistance properties of both systems are relatively poor. In any case, our investigations demonstrate that our design is viable for the realization of hydrophilic and photoswitchable molecular assemblies. In principle, innovative fluorescent probes for biomedical applications can evolve from these studies, if methods to improve their fatigue resistance properties and optimize their reisomerization kinetics can be identified. † Part of the "Larry Dalton Festschrift".

Dihydronaphthalene‐Fused Boron–Dipyrromethene (BODIPY) Dyes: Insight into the Electronic and Conformational Tuning Modes of BODIPY Fluorophores

“…BODIPYs are also frequent building blocks in molecular optoelectronic devices, energy-transfer cascades or multimode switches. [8][9][10][11][12][13] The literature on syntheses of new BODIPYs and their properties is abundant. Simple, alkyl-substituted dipyrrin BODIPYs, however, display absorption and emission bands with maxima only in the region of 480-540 nm so that today considerable effort is being made to shift the optical properties to the red.…”

Fluorescent Switches Based on Photochromic Compounds

“…Similarly, several photochromes can be attached to a single fluorescent polymer [83,84] or a fluorophore can first be connected to a photochrome and then multiple copies of the resulting dyad can be attached to a macromolecular chain. [85] For example, the co-polymer 16a ( Figure 13) bears pendant fluorophore-photochrome dyads along its macromolecular backbone in addition to hydrophilic polyethylene glycol chains. [85] Specifically, this co-polymer has an average of 15 hydrophilic tails per dyad and, as a result, is soluble in aqueous environments.…”

“…[85] For example, the co-polymer 16a ( Figure 13) bears pendant fluorophore-photochrome dyads along its macromolecular backbone in addition to hydrophilic polyethylene glycol chains. [85] Specifically, this co-polymer has an average of 15 hydrophilic tails per dyad and, as a result, is soluble in aqueous environments. The 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophores of this macromolecular construct emit at 545 nm (a in Figure 13) after excitation.…”

Molecular Implementation of Sequential and Reversible Logic Through Photochromic Energy Transfer Switching

“…This has been accomplished in liquid solution, [30] in polymers, [31] on nanoparticles [32] and in live cells. [33] As shown in Scheme 1, spiropyran photochromes combine the use of photonic and chemical input signals.…”