Syntheses and Photophysical Properties of meso‐Phenylene ridged Boron Dipyrromethene Monomers, Dimers and Trimer

Abstract

Multichromophoric boron dipyrromethene (BODIPY) dyes have been efficiently synthesized from a one‐pot condensation of acyl chloride with 2,4‐dimethylpyrrole and have been converted to energy transfer cassettes through a one‐pot Knoevenagel condensation. Various BODIPYs containing 2‐ketopyrrole unit were also isolated as the side products and one of their BF2 complex was also isolated from these condensation reactions. The fluorescence quantum yields of these phenylene bridged dimers and trimer are much lower than those of their corresponding monomers. A significant decrease of the fluorescence quantum yield was observed in most polar solvents for these dimers and trimer, which may be due to a possible symmetry breaking resulted intramolecular charge transfer (ICT) in the excited state. Efficient energy transfer between the donor and acceptor was observed in these energy transfer cassettes, which could be useful as large pseudo‐Stokes shift fluorescent dyes with potential applications in diverse fields.

Influence of molecular design on radical spin multiplicity: characterisation of BODIPY dyad and triad radical anions

“…All six compounds exhibited similar fluorescence, typical of BODIPY species functionalised at the meso-position with aryl groups. 22,27,28 Spectra exhibited small Stoke's shifts (~20-30 nm) and quantum yields less than 0.03 in all cases except for compound 4. 4 exhibited the smallest Stoke's shift, 18 nm, and the longest fluorescence lifetime of 9 ns and this was considered to result from the inhibition of free rotation at the meso position in 4 compared to others in the series.…”

“…26 It should be noted that alternative synthetic strategies have been used to prepare related BODIPY dyad and triad systems in slightly higher yields replacing the aldehyde precursor with the corresponding acyl chloride. 28 The single crystal structures of 1, 2 and 3 were determined from crystals grown by the slow diffusion of MeOH into solutions of the compounds in CH2Cl2. Attempts to grow single crystals of 4-6 using analogous conditions were unsuccessful.…”

“…Synthetic strategies for the formation of BODIPY dyads 26,27 and a small number of triads 28 with various geometries have been reported. Thus, we decided to explore, for the first time, the behavior of reduced BODIPY dyads and triads and in particular the multiplicity of these radical anion species.…”

Tuning the Photonic Behavior of Symmetrical bis-BODIPY Architectures: The Key Role of the Spacer Moiety

“…This trend could be understood in terms of a higher probability of the spacer-induced ICT owing to the closer proximity of the electron-donor amine to the electron-acceptor BODIPY subunits (Figure 4). Nevertheless, this drastic decrease of the fluorescence signal could demonstrate an additional pathway of non-radiative deactivation, since an ICT could also be promoted between the electronic clouds of the BODIPYs (Yu et al, 2015; Li et al, 2016) due to the mentioned proximity imposed by the amine-based spacers. This intramolecular deactivation process was what is known as photoinduced symmetry-breaking charge transfer (SBCT).…”

Synthesis of BODIPY dyes through postfunctionalization of the boron dipyrromethene core

“…In this case, acylation and condensation of a 2-unsubstituted pyrrole 24 are done in the same reaction, forming in situ 2-acylpyrrole 23 that immediately reacts further to symmetrical dipyrrinium salt 26 (Scheme 3). The acylating agent 25 in this reaction can be an acid chloride, 61,62 acid bromide, 63 anhydride 64 or orthoester. 65 An interesting alternative to forming symmetrical dipyrrinium salts 26 (R 1 = R 2 ) has been described by Burgess and Wu, 66 who discovered serendipitously that pyrrole-2-carbaldehyde derivatives 28 are capable of selfcondensation in the presence of phosphorous oxytrichloride (POCl3).…”