Synthesis and spectroscopic studies of diaza-8-crown-4-dinitrophenyl ethers

ABSTRACT

The macrocycles 3,7-bis(3-nitrophenyl)-1,5,3,7-dioxadiazocane 1 and 3,7-bis(4-nitrophenyl)-1,5,3,7-dioxadiazocane 2 were synthesised by a one-pot reaction with substituted nitroanilines and formaldehyde under acidic conditions. The same reaction with 2-nitroaniline yielded N, N’-(oxybis(methylene))bis(2-nitroaniline) 3 rather than 3,7-bis(2-nitrophenyl)-1,5,3,7-dioxadiazocane 4. The yellow powders 1–3 were characterised by ¹H/¹³C/¹⁵N NMR, FTIR and HRMS. The photophysical properties were studied by UV-visible absorption and steady-state fluorescence spectroscopy. Acid dissociation constants were determined by UV-visible absorption titrations in 1:1 (v/v) acetonitrile/water to be 0.80 and 3.1 for the meta- and para-substituted compounds 1 and 2, respectively. Compounds 1 and 2 were discovered to fluoresce in the solid-state, yellow and green, respectively, but not in solution. Density functional theory (DFT) calculations for 1–4 provide insight into the frontier molecular orbital energy levels. These compounds represent a new class of fluorescent heterocyclic building blocks for organic and supramolecular applications.

Graphical Abstract

KEYWORDS:

• Dioxadiazocanes
• macrocycle
• internal charge transfer
• nitrogen NMR spectroscopy
• solid-state fluorescence

Highlights

• Diaza-8-crown-4-dinitrophenyl ethers were synthesised and analytically characterised.

• The compounds are fluorescent in the solid-state, but not in acetonitrile solution.

• Techniques include 2D ¹H/¹³C/¹⁵N correlation NMR spectroscopy and DFT calculations.

Acknowledgments

Financial support is acknowledged from the University of Malta, the Slovenian Research Agency, the Ministry of Education, Science and Sport of the Republic of Slovenia (program no. P1-0242), the National Science Centre (Poland) within the contract number UMO-2015/17/B/ST8/01783, and EN-FIST Centre of Excellence. DFT calculations were performed at Academic Computer Centre Cyfronet AGH within GRAPHENE4 project. Prof. Robert M. Borg is thanked for his assistance with the NMR experiments. Carl Mallia is thanked for performing some MS measurements.

Disclosure statement

There are no conflicts of interest to declare by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This research was funded by the University of Malta, the Slovenian Research Agency [P1-0242] and the Polish National Science Centre [UMO-2015/17/B/ST8/01783].