Hydrogen Bond-Mediated Conjugates Involving Lanthanide Diphthalocyanines and Trifluoroacetic Acid (Lnpc 2 @TFA): Structure, Photoactivity, and Stability

• Published in: Molecules (Basel, Switzerland) Vol. 25; no. 16; p. 3638
• Main Authors: Dyrda, Gabriela, Zakrzyk, Maja, Broda, Małgorzata A, Pędziński, Tomasz, Mele, Giuseppe, Słota, Rudolf
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 10-08-2020; MDPI
• Subjects: Benzene; Benzene - chemistry; Chemical bonds; Chromophores; Conjugates; Coordination Complexes - chemistry; Coordination Complexes - radiation effects; Density Functional Theory; Hydrocarbons; Hydrogen Bonding; Hydrogen bonds; Indoles - chemistry; Kinetics; lanthanide diphthalocyanines; Lanthanoid Series Elements - chemistry; Ligands; Photolysis - radiation effects; photon upconversion; photostability; Samarium; Singlet oxygen; Singlet Oxygen - chemistry; Spectrometry, Fluorescence; Stability analysis; Structural stability; Structure-function relationships; TFA conjugates; Trifluoroacetic acid; Trifluoroacetic Acid - chemistry; Ultraviolet radiation; Ultraviolet Rays; Upconversion; UV-Vis spectra; Ytterbium; TFA conjugates; photon upconversion; singlet oxygen; lanthanide diphthalocyanines; photostability; UV-Vis spectra
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules25163638

The interaction between lanthanide diphthalocyanine complexes, LnPc
(Ln = Nd, Sm, Eu, Gd, Yb, Lu; Pc = C
H
N
, 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 LnPc
and TFA species. Conjugates are created between the LnPc
and TFA molecules via hydrogen bonds of moderate strength (>N∙∙H··) at the
- -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 LnPc
@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 LnPc
s itself. Photon upconversion through sensitized triplet-triplet annihilation was demonstrated by the TFA conjugates of Nd, Sm, Eu, and Gd.