1,7-Dipyrene-Containing Aza-BODIPYs: Are Pyrene Groups Effective as Ligands To Promote and Direct Complex Formation with Common Nanocarbon Materials?

Abstract

A series of 1,7-dipyrene-aza-BODIPY and 1,7-dipyrene-3,5-diferrocene-aza-BODIPY derivatives 5a–e with pyrene ligands covalently attached to the β-pyrrolic positions of the boron-azadipyrromethene (aza-BODIPY) core have been prepared and characterized by NMR, UV–vis, and steady-state fluorescence spectroscopy; high-resolution mass spectrometry; and X-ray crystallography. The redox processes of these donor–acceptor aza-BODIPY systems were investigated by electrochemistry (cyclic voltammetry and differential pulse voltammetry methods) and spectroelectrochemistry. The potential of the closely spaced 1,7-dipyrene fragments to promote formation of noncovalent π-complexes with nanocarbon materials (C60, C70, (6,5)-single-walled carbon nanotube, and graphene) was explored. UV–vis, steady-state fluorescent, and time-resolved transient absorption spectroscopy data indicated that the interaction between the new pyrene-aza-BODIPYs and C60 or C70 fullerenes in solution is weak, and time-resolved transient absorption spectroscopy provided no evidence of photoinduced electron transfer. X-ray crystallography on a binary solid of aza-BODIPYs 5b and C60 was indicative of a pyrene–pyrene rather than pyrene–C60 interaction motif, whereas fullerenes were found to form close contacts with the electron-rich B,O-chelated part of aza-BODIPY 5b. In contrast, pyrene–pyrene and pyrene–C60 but not aza-BODIPY–C60 interactions were observed in the crystal structure of aza-BODIPY 5d and C60. Density functional theory (DFT) and time-dependent DFT calculations were used to support conclusions based on experimental data and are suggestive of rather weak interaction energies between 1,7-dipyrene-aza-BODIPYs and nanocarbon materials. Direct comparison with an analogous control compound lacking the pyrene ligands demonstrated that the pyrene substituents were ineffective at promoting and directing complex formation with nanocarbon materials. A common measurement of complex formation, emission loss in the presence of a nanocarbon acceptor, was demonstrated to have an alternative explanation in these systems, and the general effectiveness of using pyrene ligands to build noncovalent complexes was drawn into question.

Structure–Property Study of Homoleptic Zinc(II) Complexes of Di(arylethynyl) Azadipyrromethene as Nonfullerene Acceptors for Organic Photovoltaics: Effect of the Aryl Group

“…The distances do not appear to correlate with the size of the aryl groups. This observation is consistent with the aryl groups having weak interactions that are not strong enough to facilitate structural assembly . For comparison, the distance and angle for pentacene are 4.7 Å and 53°, respectively, using our measurement method applied to the published pentacene crystal structure, see Figure S13 .…”

“…This observation is consistent with the aryl groups having weak interactions that are not strong enough to facilitate structural assembly. 19 For comparison, the distance and angle for pentacene are 4.7 Å and 53°, respectively, using our measurement method applied to the published pentacene crystal structure, see Figure S13. 20 We conclude that the distances we observed for the T-shaped intermolecular interactions are within the range possible for good charge transport.…”

Ferrocene: An unrivaled electroactive building block for the design of push-pull dyes with near-infrared and infrared absorptions

“…The second component in the 200-250 ps timescale is typical from ferrocene-BOD-IPY diads with charge transfer states at low energy. In 2018, the design of aza-BODIPY bearing ferrocene substituents for the elaboration of π-complexes with carbon nanotubes was examined [109]. The peripheral functionalization of aza-BODIPY is less versatile than that of BOD IPYs as the group that will further become the substituent of the pyrrole groups at the α-position is introduced in the first step of the four-step synthesis and not at the end, as classically done for the functionalization of BODIPYs (see Fig.…”

Synthesis and photophysical properties of nitrated aza-BODIPYs

“…In the past decade, boron difluoride chelates of the aza-dipyrromethene core (aza-BODIPY) have experienced a surge of interest due to their intense absorption and emission profiles in the near-infrared (NIR) region. 1–5 These properties make them exciting candidates for application in both the physical and biological sciences which include their use as sensors in molecular imaging, 6–16 light-activated singlet oxygen generating therapeutics, 17–24 solar cells, 25–29 and non-linear optical materials. 30–33 In many of these applications, a central research component involves the search for an effective method to bathochromically shift aza-BODIPY absorption and emission profiles.…”