MixedN-aryl/alkyl substitution favours an unusual tautomer of near-infrared absorbing azacalixphyrins

This work depicts the synthesis of a new azacalixphyrin presenting both aryl and alkyl substituents. The joint experimental and theoretical study supports that the substitution pattern favour an unusual 5–7 tautomer.

Fused bis-azacalixphyrin that reaches NIR-II absorptions

The fusion of two azacalixphyrins produces a new class of NIR-II dyes showing an intense absorption band in the 1000–1200 nm NIR range.

Azacalixphyrins as NIR photoacoustic contrast agents

Near-infrared (NIR) azacalixphyrins bearing aryl substituents strongly impacting the physico-chemical properties of the macrocycles were designed, enabling hyperchromic and bathochromic shifts of the absorption compared to their N-alkylated analogues. This engineering enhances the photoacoustic response under NIR excitation, making azacalixphyrins promising organic contrast agents that reach the 800-1000 nm range.

Central substitution of azacalixphyrins: a strategy towards acidochromic NIR dyes

A new substitution pattern of azacalixphyrins is proposed and assessed with theoretical tools.

On the structures, spin states, and optical properties of titanium, platinum, and iron azacalixphyrins: a DFT study

Azacalixphyrins (ACP) constitute a new class of macrocycles isoelectronic and isostructural to porphyrins. Herein, we report the first theoretical investigation of the properties of the ACP macrocycles metallated at their centre by titanium, platinum, and iron ions. We considered both the original phenyl-type ACP and new pyridyl-type forms. Our results indicate that the metallation greatly impacts the global structure of the macrocycle through pseudo Jahn-Teller effects, giving rise to a possible conformational transition between D_2d and S₄ structures. Such an effect could not be found in the metal-free ACPs. In addition, we find that, in contrast to the purely singlet platinum ACPs, and the purely triplet iron ACPs, several spin states are energetically close in the titanium ACPs, especially when weak field ligands are bound in axial positions to the metallic centre. According to TD-DFT calculations, metallation also tunes the optical properties. In particular, the absorption band in the near infrared region undergoes a hypsochromic shift of ca. 100-200 nm when going from the D_2d to the S₄ structures. We quantify how the addition of electroactive ligands in the axial position can increase or tune down these spectral changes. This contribution therefore supports the development of ACP coordination complexes.

N-Substituted Azacalixphyrins: Synthesis, Properties, and Self-Assembly

Pre- and postintroduction of substituents with respect to the macrocyclization step leads to previously unknown N-substituted azacalixphyrins. The stepwise synthetic approach has been studied in detail to highlight the key role of the N-substituents of the precursors and/or intermediates in terms of reactivity. Based on a combined experimental and theoretical investigation, the relationship between the properties of the macrocycles and their degree of substitution is rationalized. Depending on the nature of the N-substituents, the formation of supramolecular ribbon-like structures could also be observed, as demonstrated by combined TEM, SEM, AFM, and FTIR experiments.

Computational (DFT and MP2) and spectral interpretations, normal coordinate analysis, force constants and barriers to internal rotations of Trimethylacetonitrile

The Raman (3500[Formula: see text]cm[Formula: see text]100[Formula: see text]cm[Formula: see text] and IR spectra (4000[Formula: see text]cm[Formula: see text]400[Formula: see text]cm[Formula: see text] of liquid trimethylacetonitrile (C5H9N, TMA) have been obtained. In addition, the 1H and [Formula: see text]C NMR spectra of TMA were obtained in DMSO-[Formula: see text] and CDCl3. The staggered conformer (C[Formula: see text] was favored using MP2 and DFT(B3LYP/[Formula: see text]B97XD) quantum mechanical calculations utilizing a 6-311[Formula: see text]G(d,p) basis set. High energy difference estimates of 4534[Formula: see text]cm[Formula: see text]5338[Formula: see text]cm[Formula: see text] (12.96[Formula: see text]kcal/mol[Formula: see text]15.26[Formula: see text]kcal/mol) were predicted, along with three imaginary torsion frequencies for the eclipsed conformer, therefore considered a transition state. The 1H and [Formula: see text]C NMR chemical shifts were predicted with B3LYP and [Formula: see text]B97XD methods using the GIAO approximation and 6-311[Formula: see text]G(d,p) basis set. B3LYP frequencies calculation is favored herein owing to the relatively good compilation with the experimental measurements. The computed structural parameters are well correlated to those reported from electron diffraction and microwave studies. Moreover, the [Formula: see text]C[Formula: see text]H coupling constant was estimated and found consistent with that observed for the sample dissolved in DMSO-[Formula: see text]/CDCl3 solvents. Using the observed methyl torsion at 266[Formula: see text]cm[Formula: see text] in gas phase and the kinetic parameter F number, a potential function (V[Formula: see text] of [Formula: see text][Formula: see text]cm[Formula: see text]([Formula: see text][Formula: see text]kcal/mol) was obtained, this barrier to internal rotation is well correlated to 1527[Formula: see text]cm[Formula: see text] (4.37[Formula: see text]kcal/mol) predicted from MP2/6-311[Formula: see text]G(d,p) potential surface scan. Aided by the predicted wavenumbers and their IR intensity/Raman activity, the observed IR/Raman bands were intensively discussed and therefore assigned to their corresponding fundamentals, in agreement with novel normal coordinate analysis and potential energy distributions (PEDs).

Effects of chemical substitutions on the properties of azacalixphyrins: a first-principles study

Azacalixphyrins are particularly stable macrocycles absorbing light up to the near infrared region, and we present here the first investigation of the impact of substitutions on their properties.