We demonstrate herein that both alcohols and phenols can be tagged with a BODIPY (borondipyrromethene) moiety to yield highly fluorescent products. Thus, 8-(methylthio)-BODIPY (1) undergoes an S(N)Ar-type reaction with a host of alcohols and phenols in the presence of a base and a Cu(I) additive. The BODIPY dyes bearing alkoxy or nonfunctionalized phenoxy moieties are characterized by a highly efficient fluorescence emission, regardless of the media, in the blue-green part of the visible region. Complementary to this, the presence of electron-donor groups at the aryl ring leads to an intramolecular charge-transfer process, which quenches the fluorescence mainly in polar media. In addition to simple alcohols and phenols, four natural products (eugenol, menthol, cholesterol, and estrone) were labeled in a simple fashion. X-ray structures of the cholesterol and estrone derivatives are discussed. In fact, the BODIPY bearing cholesterol stands out as a bright fluorescence biological marker.

We report herein spectroscopy and computational results that illustrate an efficient intramolecular deactivation pathway for meso-unsaturated boron-dipyrromethene (BODIPY) dyes in their singlet excited state. Our results show that the mechanism hinges on the structural flexibility imparted by the boron atom and on the energetic stabilization conferred by extending the conjugation into the meso substituent, which is otherwise unconjugated in the ground state. Following photoexcitation, rotation along the dihedral angle of the meso-unsaturated group results in its conjugation at the expense of shifting one pyrrole moiety in dipyrrin out of the plane. Internal conversion to an energetically hot, ground-state species efficiently competes with emission. The mechanism applies to meso-vinyl, -formyl, and -iminyl moieties. The presence of methyl groups at positions C1 and C7 exacerbates the energetic penalty toward conjugation of the meso groups leading to a small energy gap between relaxed excited state and ground state and undetected emission quantum yields. Importantly, methyls at C1 and C7 prevent nonradiative deactivation in meso-aryl moieties, illustrating that when push comes to shove, the energetic (kinetic) barrier toward reaching conjugation is too large for aryl moieties but low enough for smaller groups to effectively compete with radiative transitions. Wisely chosen meso-unsaturated BODIPY dyes may serve as richly sensitive platforms for the preparation of novel fluorogenic substrates to monitor chemical reactions or to probe the rigidity of their surrounding environment.

Several new examples of meso-(het)arylBODIPY were prepared via the Liebeskind-Srogl (L-S) cross-coupling reaction of the Biellmann BODIPYs (1a,b) and aryl- and heteroarylboronic acids in good to excellent yield. It was shown that this reaction could be carried out under microwave heating to shorten reaction times and/or increase the yield. It was illustrated that organostannanes also participate in the L-S reaction to give the corresponding BODIPY analogues in short reaction times and also with good to excellent yields. We analyze the role of the substituent at the sensitive meso position in the photophysical signatures of these compounds. In particular, the rotational motion of the aryl ring and the electron donor ability of the anchored moieties rule the nonradiative pathways and, hence, have a deep impact in the fluorescence efficiency.

The reactivity of squarylferrocenes was studied in the addition of several N-centered nucleophiles. A total of seven simple amines (primary and secondary) were added to both monosquarylferrocene and 1,1′-bissquarylferrocene to generate 14 ferrocenylsquaramides in 85-98%. Likewise, five aminoesters were added to the same scaffolds to produce a novel family of 10 ferrocene-aminoester conjugates in good to excellent yields (57-95%).