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.

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

“…[15] Single crystal X-ray structural analyses of precursors 2 and 3 revealed near-planar structures (Supporting Information, Figures S25 and S26). [17] This planarity and the rigidity were considered likely to favor the formation of larger cyclic systems,asseen experimentally (see below).…”

“…As ingle crystal X-ray diffraction analysis of crystals grown by the slow diffusion of hexanes into CHCl 3 solutions of 4 revealed ag able-type structure along with the two sp 3 hybridized meso-like position bearing pentafluorophenyl substituents. [17] Presumed p-p interactions between the naphthalene units of an eighboring molecule were inferred from the short separations (3.517 ), which presumably serve to stabilize the one-dimensional array seen in the solid state (Figure 1a-c). However,n oe vidence of aggregation was observed when 4 was dissolved in dichloromethane (Figures S32-S35).…”

“…Further insights into the molecular structure of calix- [16]phyrin 5 came from single-crystal X-ray structural analyses of crystals grown through the slow diffusion of hexanes into ad ichloroethane solution of 5. [17] In the solid state, 5 exists as athree-dimensional box-like structure wherein four bis-naphthobipyrrolylmethene subunits are connected through four sp 3 -hybridized meso carbon atoms.T he pentafluorophenyl groups are oriented towards the macrocyclic cavity.Onthe other hand, the four meso-mesityl groups point toward the outside of the cavity (Figure 2).…”

Orthogonally aligned cyclic BODIPY arrays with long-lived triplet excited states as efficient heavy-atom-free photosensitizers

“…Two types of cyclic BODIPY arrays were also synthesized from BODIPY monomers through self-coupling or condensation with pentafluorobenzaldehyde. 15 A sole example of elegant cyclic BODIPY array CB4 linked through boron atoms was reported by Nabeshima and co-workers 16 using the reaction of catecholyldipyrrin with boron trichloride. Despite the low yields (less than 5%) of this one-pot reaction, the resultant CB4 was a nice supramolecular host for alkali metal ions.…”

Macrocyclic Arenes Functionalized with BODIPY: Rising Stars among Chemosensors and Smart Materials

“…Their sensing mechanisms mainly include photo-induced electron transfer (PET), intramolecular charge transfer (ICT), excited-state intermolecular proton transfer (ESIPT), and metal-to-ligand charge transfer (MLCT). In addition, BODIPY units have been demonstrated to be potent building blocks to construct various BODIPY-based macrocycles (Figure 2c), where BODIPY moieties are introduced into the macrocyclic skeletons rather than act as the substituents [59][60][61][62][63][64][65]. Up until now, the research related to the combination of macrocyclic arenes and BODIPY dyes has not been systematically summarized.…”