Tuning linear dichroism/birefringence (LDLB) contributions in VCD spectra of tartaric acid-TPPS4 porphyrin films

Year: 2025

Authors: Mazzeo G., Fusi M., Abbate S., Zagami R., Castriciano MA., Romeo A., Scolaro L.M., Longhi G.

Autors Affiliation: Univ Brescia, Dipartimento Med Mol & Traslaz, Viale Europa 11, I-25123 Brescia, Italy; Ist Nazl Ottica CNR, Unita Brescia, Via Branze 45, I-25123 Brescia, Italy; Univ Messina, Dipartimento Sci Chim Biol Farmaceut Ambientali, V le F Stagno Alcontres 31, I-98166 Messina, Italy.

Abstract: Vibrational circular dichroism (VCD) is employed to investigate chiral-templation of d and l tartaric acids (TA) which, according to electronic circular dichroism (ECD) studies, drive tetrakis-(4-sulfonatophenyl)porphyrin (TPPS4) to self-assemble into chiral J-aggregates. TPPS4/TA solutions, prepared in both H2O and D2O, are drop cast on CaF2 plates. VCD spectra of corresponding films are not affected by rotating the samples around the incident beam, but undergo dramatic changes, even sign reversal, by flipping the samples from front to rear position, depending on acid content. The observed IR absorption features are mainly due to vibrational transitions of TA. The dissymmetry ratio g for the observed features is of the order of 10-2, which is quite high for vibrational phenomena: the semi-sum spectra in the front-rear positions can be considered as representative of intrinsic VCD phenomena, the semi-difference is associated with linear dichroism-linear birefringence components (LDLB term). In this study, we show that TPPS4 and TA, when mixed appropriately following the specified protocols, yield films in which the VCD and LDLB components can be effectively modulated.

Journal/Review: PHYSICAL CHEMISTRY CHEMICAL PHYSICS

More Information: Funding by the Italian Ministry of University and Research (MUR): projects SMART HELIX, prot. 2022B3EFJH, INVESTCPE, prot. 2022CXHY3A, CHI-EP (PRIN_2022HPW79T_002) and Next Generation EU, PNRR Samothrace Project (ECS00000022) is acknowledged. The authors acknowledges also the Italian Project PNNR I-PHOQS-Integrated Infrastructure Initiative in Photonic and Quantum Science CUP B53C22001750006 and Prof. Antonio Leonardi for SEM and optical microscopy. The authors wish to thank the reviewers, who provided insightful suggestions for improving the manuscript and for pointing out relevant literature.
KeyWords: Vibrational Circular-dichroism; Supramolecular Chirality; Absolute-configuration; Optical-activity; Acid; Spectroscopy; Absorption
DOI: 10.1039/d5cp03069b