What question did this study set out to answer?

This study aims to explore the relationship between anion size and the conformational properties of guanidinopropionate derivatives to optimize optical performance.

April 15, 2026

Anion Size‐Dependent Conformational Folding of Guanidinopropionate: Enabling Tunable Birefringence and Balanced Second‐Harmonic Generation Performance

Key Points

This study aims to explore the relationship between anion size and the conformational properties of guanidinopropionate derivatives to optimize optical performance.
Synthesize four guanidinopropionates with different anions (X = Cl-, Br-, [HSeO3]-, [NH2SO3]-).
Analyze structural changes using dihedral angles and bond rotations.
Measure optical properties such as birefringence and second-harmonic generation (SHG).
Utilize DFT calculations to assess conformational stability and electronic properties.
Dihedral angle between π-conjugated planes decreases from 175° to 65° with different anions.
Birefringence (Δn) reduces from 0.20 in GPC to 0.11 in GPMS, indicating improved optical performance.
GPMS shows a substantial band gap of 5.63 eV alongside a notable SHG response of 3.3 × KH2PO4.
DFT findings suggest that conformational folding leads to tunable electronic properties across guanidinopropionates.

Abstract

The structure-property relationship investigations constitute a fundamental paradigm for the rational design and synthesis of high-performance functional materials. Herein, four guanidinopropionates (C4H10N3O2)X (X = Cl- (GPC), Br- (GPB), HSeO3- (GPSe), and NH2SO3- (GPMS)) were reported. Anion-size-dependent modulation of the C2─C3 single bond rotation (linking guanidino and carboxylic π-conjugated groups) induces a reduction of the dihedral angle between the two π-conjugated planes (α) from 175° to 65°. With such a coplanarity reduction, the optical anisotropy property (birefringence, Δn) decreases from an excessive 0.20 in GPC to a favorable 0.11 in GPMS. Remarkably, GPMS also exhibits a large band gap (5.63 eV) and an enhanced second-harmonic generation (SHG) response (3.3 × KH2PO4). DFT reveals these four conformations are nearly degenerated, and the HOMO-LUMO gap, polarizability anisotropy, and hyperpolarizability across these four conformers are broadly tunable. This work first demonstrates how conformational folding control of flexible π-conjugated units effectively modulates and optimally balances three critical yet mutually restrictive parameters essential for high-performance SHG materials.

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Anion Size‐Dependent Conformational Folding of Guanidinopropionate: Enabling Tunable Birefringence and Balanced Second‐Harmonic Generation Performance

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