CHARGE-TRANSFER INTERACTIONS BETWEEN NUCLEIC-ACID BASES AND STRONG ACCEPTORS

The regularities of the donor‐acceptor interaction of nucleic acid bases and some of their derivatives with the strong acceptor 7,7,8,8‐tetracyanoquinodimethane (TCNQ) in thin amorphous films at 77 K were studied using UV and visible spectroscopy. Purine and pyrimidine bases are shown to form charge transfer TCNQ complexes whose band energies hνct = Ip − EA − (H* − H0) are linearly dependent of the donor ionization potential Ip. Calculated differences between the interaction energies of uncharged molecules and ion radicals, ΔE ≈ 3.0 eV, are in good agreement with experimental variations of the complex dissociation energies in the ground and excited states, (H* − H0) = 2.73 eV. Annealing of the films of complexes containing cytosine, 1‐methylcytosine, uracil, and caffeine leads to ordering of their structure and the formation of ion radical salts. Copyright © 1979 John Wiley & Sons, Inc.