Spectrophotometric studies on the thermodynamic properties of charge-transfer complexes between m-DNB (1,3-dinitrobenzene) with aliphatic amines in DMSO and determination of the vertical electron affinity of m-DNB.

1,3-Dinitrobenzene formed colored 1:1 complexes with aliphatic amines (chromogenic agents) like isopropylamine,ethylenediamine, tetraethylenepentamine and bis(3-aminopropyl)amine in DMSO having absorption maxima at 563 nm, 584 nm, 580.5 nm and 555 nm respectively. The complexes were stable for more than 24 h. The accurate association constants KAD and other thermodynamic parameters were determined with D and A usually in stoichiometric ratios. But in case of m-DNB and bis(3-aminopropyl)amine, the association constants KAD and the thermodynamic parameters were also determined using Benesi-Hildebrand equation to show the variations of KAD under different conditions. ΔG° values were found to be negative in all cases resulting from exothermic enthalpy changes and favourable entropy changes. The energies of transition for the CT complexes hνCT found experimentally were considerably different from the energies of transition (from HOMO of donor to LUMO of acceptor) calculated using AM1 but the differences were considerably reduced using DFT calculations. The vertical electron affinity of m-DNB was calculated using the method suggested by Mulliken. However, no FTIR measurements of the complexes could be made due to experimental limitations.