Abstract
Achieving high thermal stability and control of supramolecular organization of functional dyes in sensors and nonlinear optics remains a demanding task. This study was aimed at the evaluation of thermal behavior and Langmuir monolayer characteristics of topologically varied nitrothiacalixarene multichromophores and phenol monomers. A nitration/azo coupling alkylation synthetic route towards partially O-substituted nitrothiacalixarenes and 4-nitrophenylazo-thiacalixarenes was proposed and realized. Nuclear magnetic resonance (NMR) spectroscopy and X-ray diffractometry of disubstituted nitrothiacalix[4]arene revealed a rare 1,2-alternate conformation. A synchronous thermal analysis indicated higher decomposition temperatures of nitrothiacalixarene macrocycles as compared with monomers. Through surface pressure/potential-molecular area measurements, nitrothiacalixarenes were shown to form Langmuir monolayers at the air–water interface and, through atomic force microscopy (AFM) technique, Langmuir–Blodgett (LB) films on solid substrates. Reflection-absorption spectroscopy of monolayers and electronic absorption spectroscopy of LB films of nitrothiacalixarenes recorded a red-shifted band (290 nm) with a transition from chloroform, indicative of solvatochromism. Additionally, shoulder band at 360 nm was attributed to aggregation and supported by gas-phase density functional theory (DFT) calculations and dynamic light scattering (DLS) analysis in chloroform–methanol solvent in the case of monoalkylated calixarene 3. Excellent thermal stability and monolayer formation of nitrothiacalixarenes suggest their potential as functional dyes.
Highlights
Control of supramolecular interactions plays an increasing role in the performance of organic dyes [1] and macrocycles [2] in a variety of applications including nonlinear optical (NLO) materials, sensors, drug carriers, catalysts, and explosives
Calixarenes containing nitro groups on the upper rim offer potential applications as NLO materials [8], redox probes [9], and colorimetric chemosensors [10] due to the formation of a
Analogous type II disubstituted azo derivative was not isolated as an individual product after column chromatography due to the impurity of monoazothiacalix[4]arene and full conversion of this impurity into target product was not achieved even after a one-week heating of azothiacalixarene 4 at 60 ◦ C with an eight-fold excess of diazonium salt. These results show that only nitration/azo coupling alkylation sequence is effective for synthesis of type III nitrocalixarene chromophores, whereas inverse functionalization sequence results only in partial upper rim substituted type II chromophores
Summary
Control of supramolecular interactions plays an increasing role in the performance of organic dyes [1] and macrocycles [2] in a variety of applications including nonlinear optical (NLO) materials, sensors, drug carriers, catalysts, and explosives. Calix[4]arenes should be mentioned, whose facile stereo-, regio-, and iteroselective modifications [3] provide diverse architectures displaying multipoint binding [4], allosteric regulation [5], and self-assembly behavior [6,7]. Calixarenes containing nitro groups on the upper rim offer potential applications as NLO materials [8], redox probes [9], and colorimetric chemosensors [10] due to the formation of a.
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