Hydrogen Bond-Mediated Conjugates Involving Lanthanide Diphthalocyanines and Trifluoroacetic Acid (Lnpc2@TFA): Structure, Photoactivity, and Stability.

Gabriela Dyrda,Małgorzata A Broda,Maja Zakrzyk,Tomasz Pędziński,Rudolf Słota,Giuseppe Mele

doi:10.3390/molecules25163638

Abstract

The interaction between lanthanide diphthalocyanine complexes, LnPc2 (Ln = Nd, Sm, Eu, Gd, Yb, Lu; Pc = C32H16N8, phthalocyanine ligand) and trifluoroacetic acid (TFA) was investigated in benzene, and the stability of the resulting molecular system was assessed based on spectral (UV-Vis) and kinetic measurements. Structural Density Functional Theory (DFT) calculations provided interesting data regarding the nature of the bonding and allowed estimating the interaction energy between the LnPc2 and TFA species. Conjugates are created between the LnPc2 and TFA molecules via hydrogen bonds of moderate strength (>N∙∙H··) at the meso- -bridges of the Pc moieties, which renders the sandwich system to flatten. Attachment of TFA is followed by rearrangement of electronic density within the chromophore system of the macrocycles manifested in considerable changes in their UV-Vis spectra and consequently the color of the studied solutions (from green to orange). The LnPc2@TFA conjugates including Nd, Sm, Eu, and Gd appeared evidently less photostable when exposed to UV radiation than the related mother compounds, whereas in the case of Yb and Lu derivatives some TFA-prompted stabilizing effect was noticed. The conjugates displayed the capacity for singlet oxygen generation in contrast to the LnPc2s itself. Photon upconversion through sensitized triplet–triplet annihilation was demonstrated by the TFA conjugates of Nd, Sm, Eu, and Gd.

Highlights

Phthalocyanine derivatives are ranked among one of the most important molecular materials.From among a great number of possible structural variations, the sandwich complexes of the lanthanide metals series offer a wide range of useful features meeting the demands for smart chemical components to be used for versatile purposes [1,2]
The peculiar molecular system consisting of a trivalent lanthanide (Ln) ion coordinated by two Pc macrocycles (Figure 1) renders the LnPc2 semiconductors display a considerably smaller energy bandgap and much better electrical conductivity and higher charge mobility compared with typical metallophthalocyanines
In the present work we have studied the impact of trifluoroacetic acid (TFA) species on selected diphthalocyanines including the trivalent ions of Nd, Sm, Eu, Gd, Yb, and Lu

Summary

Introduction

From among a great number of possible structural variations, the sandwich complexes of the lanthanide metals series offer a wide range of useful features meeting the demands for smart chemical components to be used for versatile purposes [1,2]. These include essentially modern electronics, optoelectronics, and catalytic applications. 2 2ofof1515 conductivity and higher charge mobility compared with typical metallophthalocyanines (e.g., CuPc, ZnPc) [3,4] This is considered crucial for intermolecular charge transfer in film integrated circuits, catalytic systems, and photoactive composites. The LnPc2s effectively absorb the photonic energy from the UV and red-edge range which may boost the electron transfer in photo-conducting energy from the UV and red-edge range which may boost the electron transfer in photo-conducting electronic electroniccomponents

Methods

Results

Conclusion