Photonic Amplification by a Singlet-State Quantum Chain Reaction in the Photodecarbonylation of Crystalline Diarylcyclopropenones

Abstract

The photochemical decarbonylation of diphenylcyclopropenone (DPCP) to diphenylacetylene (DPA) proceeds with remarkable efficiency both in solution and in the crystalline solid state. It had been previously shown that excitation to the second electronic excited state (S(2)) of DPCP in solution proceeds within ca. 200 fs by an adiabatic ring-opening pathway to yield the S(2) state of DPA, which has a lifetime of ca. 8 ps before undergoing internal conversion to S(1) (Takeuchi, S.; Tahara, T. J. Chem. Phys. 2004, 120, 4768). More recently, we showed that reactions by excitation to S(2) in crystalline solids proceed by a quantum chain process where the excited photoproducts transfer energy to neighboring molecules of unreacted starting material, which are able to propagate the chain. Quantum yields in crystalline suspensions revealed values of Phi(DPCP) = 3.3 +/- 0.3. To explore the generality of this reaction, and recognizing its potential as a photonic amplification system, we have synthesized nine crystalline diarylcyclopropenone derivatives with phenyl, biphenyl, naphthyl, and anthryl substituents. To quantify the efficiency of the quantum chain in the crystalline state, we determined the quantum yields of reaction for all of these compounds both in solution and in nanocrystalline suspensions. While the quantum yields of decarbonylation in solution vary from Phi = 0.0 to 1.0, seven of the nine new structures display quantum yields of reaction in the solid that are above 1. The chemical amplification that results from efficient energy transfer in the solid state, analyzed in terms of the quantum yields determined in the solid state and in solution (Phi(cryst)/Phi(soln)), reveals quantum chain amplification factors that range from 3.2 to 11.0. The remarkable mechanical response of the solid-to-solid reaction previously documented with macroscopic crystals, where large single-crystalline specimens turn into fine powders, was investigated at the nanometer scale. Experiments with dry crystals of DPCP analyzed by atomic force microscopy showed the formation of DPA in the form of isolated crystalline specimens ca. 35 nm in size.

Toward Carbon Monoxide–Based Therapeutics: Critical Drug Delivery and Developability Issues

“…86-89 Fluorescein analogue 8 (Figure 3) was the first reported transition metal free and water soluble photo-sensitive CO-RM. 47 After irradiation with visible light (λ = 503 ± 15 nm) in phosphate buffer saline (PBS) buffer (pH = 7.4), compound 8 could release CO with a half-life of around 4.5 h. This release rate is much slower compared to most metal based CO-RMs, which tend to have half-lives in the range of minutes.…”

Cyclopropenone-caged Sondheimer diyne (dibenzo[a,e]cyclooctadiyne): a photoactivatable linchpin for efficient SPAAC crosslinking

“…15 This reaction can be induced by NIR light under two-photon excitation conditions 16 and proceeds smoothly in the solid state. 17 We have already employed this reaction for the generation of reactive triple bonds in ynols, 18 enediynes, 19 and dibenzocyclooctynes. 20 Irradiation of bis-cyclopropenone 1 (photo-DIBOD) results in the formation of the Sondheimer diyne 2 , which, in turn reacts with two azide-functionalized substrates to create a stable covalent cross-link (Scheme 1).…”

“…Garcia-Garibay has previously reported that irradiation of the nanocrystalline suspension of diphenylcyclopropenone results in the efficient decarbonylation of the substrate. 17 In fact, the quantum yield of the process in the solid state is about 4 times higher than in solution due to “quantum chain reaction.” 17,30 The nanocrystalline suspension of photo-DIBOD 1a was prepared using reprecipitation techniques. 17 A methanol solution of the substrate was slowly added to an aqueous PBS buffer containing 15 mM of SDS under sonication.…”

“…17 In fact, the quantum yield of the process in the solid state is about 4 times higher than in solution due to “quantum chain reaction.” 17,30 The nanocrystalline suspension of photo-DIBOD 1a was prepared using reprecipitation techniques. 17 A methanol solution of the substrate was slowly added to an aqueous PBS buffer containing 15 mM of SDS under sonication. Dynamic light scattering (DLS) studies performed on a photo-DIBOD suspension revealed a mean distribution of particles at 572±130 nm.…”

Efficient Photochemical Approaches for Spatially Resolved Surface Functionalization

“…Am ethod based on the photogeneration of these types of alkynes or azides would thus be desirable. [25] Interestingly,t he most widely employed strained cyclooctyne motif-although it has now been surpassed in terms of reactivity [26] and ease of synthesis [27] -is dibenzocyclooctyne (DBCO), ad iarylcyclooctyne. [23] However,P oloukhtine and Popik showed that alkynes could be formed by photolysis of cyclopropenones.…”