Helen Hölzel

Five new nonsymmetric BODIPY dyes based on the Biellmann methodology [NSBBs (nonsymmetrical Biellmann BODIPYs)] were prepared by condensation of pairs of different pyrroles with thiophosgene. Treatment of the resulting thioketones with MeI and BF₃·Et₂O/TEA yielded a wide range of products in a simple manner, with selective alkylation of each pyrrole of the indacene core and with controlled functionalization at the meso position. A comprehensive combined photophysical and computational study has been conducted to determine the impact of the alkylation pattern, as well as the role of the conformational freedom and electron coupling of 8-phenyl and 8-methylthio groups on the spectroscopic signatures of BODIPYs. The results and conclusions reached are compared with those for previously reported related analogues. We intend to provide key structural guidelines with regard to the factors that trigger the fluorescence responses and spectral shifts of multifunctional fluorophores of this family.

New nonsymmetric 8-methylthioBODIPYs featuring selective alkylation of the pyrrole systems were synthesized and their specific functionalization at the meso position was achieved. The combined photophysical and computational characterization of these dyes provides key structural guidelines for modulation of their spectral band positions, as well as their fluorescence responses.

A two-step synthetic route toward BODIPY dyes is accomplished by reaction of the readily available naphtho[1,2-c]pyrrole with various aldehydes followed by coordination of BF₂. Synthesis of the dipyrromethene is achieved by simply heating the pyrrole and aldehyde at moderate temperatures for less than 30 min. In addition to the absence of solvent this reaction does not require an acid catalyst or an oxidizing agent to achieve the dipyrromethene. Investigation of various aldehydes by this method suggests that the choice of aldehyde plays a role in the formation of either symmetric or asymmetric BODIPYs. The dyes have exceptionally high molar absorptivities (> 100000 m^–1 cm^–1) in the far visible region of the electromagnetic spectrum with intense emission and high quantum efficiency.

A series of naphthyl-fused BODIPY dyes have been synthesized by a simple two-step process. These dyes display high molar absorptivities in the far visible region of the spectrum with emission quantum efficiencies at or near unity.

A procedure for the synthesis of biaryl ketones by a palladium-catalyzed Suzuki–Miyaura cross-coupling reaction between phenyltrifluoroborates and benzoyl chlorides is described. Organotrifluoroborates are unique to other cross-coupling reagents as they have a high functional-group tolerance and are moisture-stable. Moderate to excellent yields were obtained for all substrates tested.

A procedure for the synthesis of biaryl ketones by a Pd-catalyzed Suzuki–Miyaura cross-coupling reaction between phenyltrifluoroborates and benzoyl chlorides with moderate to excellent yields is described. Organotrifluoroborates are unique to other cross-coupling reagents as they have a high functional-group tolerance and are moisture-stable.

Diels–Alder cycloaddition reactions of 1,3,5-hexatriynes with tetraphenylcyclopentadienone have been performed, and mainly gave 1,2-diethynyl-3,4,5,6-tetraphenylbenzene derivatives as products. The Diels–Alder reactions were optimized under conventional heating and microwave irradiation conditions, and showed good selectivity towards the central carbon–carbon triple bond of the triyne. Empirical evidence suggests that the selectivity of the reaction is governed predominantly by the steric demands of the end-groups of the triyne. Several of the Diels–Alder products could be further elaborated by a sequence of desilylation and oxidative homocoupling to provide dimeric products. The homocoupling reaction was optimized by Pd catalysis. The X-ray crystallographic analysis of two derivatives is reported.

Diels–Alder cycloaddition reactions of 1,3,5-hexatriynes with tetraphenylcyclopentadienone under either thermal or microwave-assisted conditions give regioisomeric products that can be interpreted based on the size of the triyne end-groups.