Acid‐Sensitive BODIPY Dyes: Synthesis through Pd‐Catalyzed Direct C(sp³)−H Arylation and Photophysics

Abstract

A novel palladium-catalyzed direct C(sp )-H arylation of the methyl group at the 8-position of BODIPY by bromoarenes was established. A deprotonative cross-coupling process was supposed to be involved in the reaction. This approach allowed us to attach electron-donating/withdrawing, halogen substituted aryls and a heteroaryl with a yield running from 55 to 99 %. Novel pH sensors, which in the absence of acid showed the occurrence of photoinduced electron transfer, were synthesized by attaching dimethylaniline to the methyl at the C8-position of BODIPY. The reference compounds with dimethylaniline directly attached to the C8-position were also synthesized and besides photoinduced electron transfer also showed a charge-transfer emission. Their photophysical properties were investigated by steady-state fluorescence, time-correlated single-photon counting and femtosecond fluorescence up-conversion. Time-dependent density functional (TD-DFT) electronic-structure calculations on the properties of the excited states corresponding to local excitation of the BODIPY core and to charge transfer were conducted. Upon addition of trifluoroacetic acid in toluene and ethanol, the partial fluorescence intensity recovery was at least an order of magnitude more efficient with the newly synthesized sensors compared to the traditional reference sensors. The improved sensitivity of these novel BODIPY-based pH sensors was attributed to less efficient proton-coupled electron transfer of the protonated species.

Cyclometalated iridium–BODIPY ratiometric O2 sensors

“…All three pyridyl-BODPYS have similar photoluminescence spectra, the notable difference being the quantum yields, which for methylene-spaced 5 is observed to be 0.99, compared to 0.30 ( 3 ) and 0.43 ( 4 ) for the aromatic pyridyl-BODIPYs. This exceptionally high quantum yield for complex 5 has also been observed in other solvents such as toluene ( Φ PL = 1.0) and ethanol ( Φ PL = 0.89), as well as in other BODIPYs with substituted benzyl substituents at the meso position 66. The fluorescence lifetimes for all of the free BODIPYs are in the ns range, with a slightly longer value for 5 (6.6 ns) when compared with 3 and 4 (1.9 and 2.7 ns, respectively).…”

“…Compounds 3 and 4 , with a meso -pyridyl and extended meso -4-pyridylphenyl linker, respectively, were accessed following known procedures,63,64 and the Lewis acid–base chemistry of these versions have been recently described by our group 65. Methylene-spaced 4-pyridinyl–CH 2 –BODIPY 5 , with an unconjugated linker between the pyridine moiety and the BODIPY core, can be prepared by the previously reported synthetic method involving a palladium-catalyzed Suzuki cross-coupling reaction 66. The bis-cyclometalated iridium fragment originates from precursors of the type Ir(C^N) 2 (CNAr dmp )(FPF 5 ) ( 2a and 2b ; C^N = cyclometalating ligand, CNAr dmp = 2,6-dimethylphenyl isocyanide), accessed via silver-mediated halide abstraction from the respective chloride-bound precursors 1a and 1b 67.…”

Assessment of local coupled cluster methods for excited states of BODIPY/Aza‐BODIPY families

“…Therefore, the latter reason involving solvent effects could be more likely especially if we take into account the previous experimental evidence on the Aniline-BODIPY. 52 In those experiments, the observation of the CT state was dependent on the solvent. The CT peak was not visible in ethanol; however, it was visible in THF.…”

Photophysics of BODIPY Dyes: Recent Advances

“…A synthetic approach for palladium-catalyzed direct C(sp 3 )-H arylation of the methyl group at the 8-position of BODIPY reported by Chong et al [57]. This approach permitted attaching electron-donating/withdrawing, halogensubstituted aryls and a heteroaryl with a yield running from 55 to 99%.…”