Abstract
Stable radicals in organic conjugated molecules are of great interest due to their magnetic signals and broad optical absorptions. In this paper, we report on naphthalene, benzoperylene, perylene, terrylene, and quaterrylene carboximides, reduced under controlled conditions, where stable metal-free solid salts of radical anions could be obtained forming darkly colored solutions with line-rich UV/Vis/NIR spectra and exhibiting special magnetic properties. The most bathochromic shift of the absorption maxima extend from 760 until 1700 nm. Persistent paramagnetic properties of the solids were observed and temperature-dependent susceptibilities are measured.Graphical abstract
Highlights
Absorption edge of organic compounds is in the ultraviolet (UV) because of large energetic gaps between the highest occupied molecular orbital (HOMO) and highest occupied molecular orbital (LUMO)
The peri-arylenebiscarboximides [5] 1 according to Scheme 1 are known for n = 1 absorbing in the UV [6, 7] to n = 4 and, n = 6 [8] absorbing in the near infrared (NIR) and are attractive starting materials for the preparation of radical anions 2 because of their high stability, electron depletion by four carbonyl groups and broad region of tuning of light absorption
The preparation of the radical anions 2 (n = 1) was successful in various solvents for both for R = alkyl and R = aryl and was indicated by the bathochromic UV/Vis absorption with a maximum at 761 nm corresponding to the absorption of the electrochemically prepared radical anions
Summary
Absorption edge of organic compounds is in the ultraviolet (UV) because of large energetic gaps between the highest occupied molecular orbital (HOMO) and highest occupied molecular orbital (LUMO). The peri-arylenebiscarboximides [5] 1 according to Scheme 1 are known for n = 1 absorbing in the UV [6, 7] to n = 4 and, n = 6 [8] absorbing in the NIR and are attractive starting materials for the preparation of radical anions 2 because of their high stability, electron depletion by four carbonyl groups and broad region of tuning of light absorption. UV/Vis/NIR spectra of electrochemically prepared 2 were indicated [11]. Chemical reduction of 1 (n = 1) was described by means of strongly alkaline dithionite [12] solution without further characterization. UV/Vis spectra of radical anions 2 were obtained by flash photolysis and spectroscopically compared [13] with the products from reduction with dithionite and with cobaltocene [14]. Cyclic triradical trianions were described [15,16,17]
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