Excitonically Coupled Cyclic BF₂ Arrays of Calix[8]‐ and Calix[16]phyrin as Near‐IR‐Chromophores

Abstract

Two giant calix[n]phyrin derivatives namely calix[8]‐ (4) and calix[16]phyrin (5), involving two and four BF2 units, respectively, were prepared through the condensation of the bis‐naphthobipyrrolylmethene‐BF2 complex (3) with pentafluorobenzaldehyde. Calix[n]phyrins 4 and 5 display extremely high extinction coefficients (3.67 and 4.82×105 m−1 cm−1, respectively) in the near‐IR region, which was taken as initial evidence for strong excitonic coupling within these cyclic multi‐chromophoric systems. Detailed insights into the effect of excitonic coupling dynamics on the electronic structure and photophysical properties of the macrocycles came from fluorescence, time‐correlated single‐photon counting (TCSPC) and transient absorption (TA) measurements. Support for these experimental findings came from theoretical studies. Theory and experiment confirmed that the coupling between the excitons depends on the specifics of the calix[n]phyrin structure, not just its size.

Near‐IR Electrochromic Dihydroindolo(2,3a)carbazole‐Based Macrocycles and Their [b]‐Annulated BODIPY Complexes

“…[ 14 ] BF 2 complexation on these macrocycles is expected to provide [b]‐annulated systems ( InCT BF 2 and InCB BF 2 ). [ 15 ] The change in the frontier molecular orbital levels are supported with decreased LUMOs with unaltered HOMOs. [ 16 ] Such lowering in the LUMO level results in a large red‐shift in the absorption spectrum extending toward the near‐IR region.…”