Propeller‐Shaped Semi‐fused Porphyrin Trimers: Molecular‐Symmetry‐Dependent Chiroptical Response

Abstract

Triple helicene‐like semi‐fused trimeric NiIIporphyrins were constructed by alkyne trimerization of an ethynyl‐substituted porphyrin and subsequent three‐fold Grignard addition to the formyl groups and acid‐catalyzed intramolecular cyclization. The presence of stereogenic sp3carbons in the central bridge leads to small inter‐porphyrin conjugative interactions as was revealed by electrochemical and optical properties. Two diastereomers with stable chiral conformations were optically resolved, and the separated enantiomers displayed considerably intense circular dichroism. Importantly, the chiroptical response ofC3‐symmetric helical isomer (|Δϵ|=830 m−1 cm−1) is 1.8 times amplified from that ofC1‐symmetric one (|Δϵ|=470 m−1 cm−1). The observed amplification has been interpreted in terms of different spatial arrangements of the three porphyrins.

Understanding the Conformational Preference of Propeller-shaped Polycyclic Aromatic Hydrocarbons

“…Non-planar, chiral polycyclic aromatic hydrocarbons (PAHs) exhibit unique photophysical and chirooptical properties. [1][2][3][4][5][6] One subclass of particular interest are the helicenes, which are molecules composed of ortho-fused aromatic rings, and that adopt a helical geometry. [7][8][9] Although helicenes hold potential for use in chiro-optical applications, low barriers to racemization and poor photo-stability towards UV light, pose significant challenges.…”

Insight into the Influence of the Chiral Molecular Symmetry on the Chiroptics of Fluorescent BINOL-Based Boron Chelates

“…Molecular symmetry plays an important role in the CPL response (see, for example, D 3 -symmetric triple pentahelicene a [ 10 ], C 2 -symmetric BODIPYs b [ 11 ], d [ 13 ] and e [ 14 ], or C 3 -symmetric porphyrin trimer c [ 12 ], in Figure 1 ), owing to its influence on the electric and magnetic transition dipole moments of the molecule involved in the circularly polarized emission [ 15 ]. However, the role of molecular symmetry in the CPL emission is not completely known yet.…”

Efficient synthesis and unit-selective π-extension of π-fused [4.3.3]propellane as a chiral building block

“…2 Because of this requirement, the synthesis of chiroptical π-conjugated systems is usually difficult as compared with that of planar ones, especially when the fused structures were constructed via multiple bond formation against large strain energy. 2,3…”