Chiral Phthalocyanines through Axial Coordination

Abstract

A novel approach to axially induce chirality on silicon phthalocyanines via a microwave-assisted route is reported. CD analysis provides spectroscopic evidence that chirality is transferred onto both Soret and Q-bands of the phthalocyanine core. A chiral naphthalenediimide ligand was found to induce the largest Cotton effect on the macrocycle absorptions.

Mapping the Chiroptical Properties of Local Domains in Thin Films of Chiral Silicon Phthalocyanines by CD Imaging

“…The g-factor ranges between −2 and +2, spanning between 10 −3 and 10 −4 for organic molecules [21]. Derivative 1 has flexible sidechains appended to the aromatic NDI, displaying the largest ellipticity in solution as shown by our previous studies [18]. The absorption pattern of film of 1 from TCE is similar to that in solution.…”

“…The SiPcs used in this study are shown in Figure 1A. We have recently reported a one-step, microwave-assisted approach to synthesize chiral SiPcs through axial coordination [18]. The three SiPcs used in this study have been synthesized via this method (full characterization in the Materials and Methods section).…”

“…The three SiPcs share common features of axial ligands bearing aromatic surfaces and chiral centers close to the Pc ring. They were chosen due to the large Cotton effect observed on both the B and Q-phthalocyanine bands [18].…”

“…The three SiPcs share common features of axial ligands bearing aromatic surfaces and chiral centers close to the Pc ring. They were chosen due to the large Cotton effect observed on both the B and Q-phthalocyanine bands [18]. Molecule 1 is a naphthalenediimide (NDI) derivative, while 2 and 3 are a pair of enantiomers based on naproxen coordinated on the SiPc core.…”

“…However, the ECD spectra of films of 2 and 3 show an opposite sign upon sample flipping (Figure 4B,C, solid lines). This is due to the coupling of linear dichroism (LD) and linear birefringence (LB) contributions, which are polarization effects that arise from sample orientation and are intrinsic anisotropic components of ECD, usually being referred to as the LDLB effect [16,18,23]. The dissymmetry g-factor of naproxen-functionalized SiPcs has values as large as 10 −1 (film of 2 in Figure 4B) and 10 −2 (film of 3 in Figure 4C).…”