Intramolecular interaction of chromophores in diprotonated dichalcones containing a biphenylene bridge structure

The relationships governing the change in the energy of intramolecular interaction of the chromophores in their diprotonated forms, i.e., the corresponding dihydroxydicarbonium ions, were analyzed on the basis of data on the electronic absorption spectra for sulfuric acid solutions of 23 unsaturated diketones containing a heterocyclic biphenylene bridge structure (the dibenzofuran, dibenzothiophene, carbazole, and 9-methylcarbazole rings). It was shown that the energy of intramolecular interaction of the chromophores increases with substitution of the heteroatom X of the bridge structure in the order O, S, NH, and NCH/sub 3/ and decreases with increase in the chain length of the conjugated chromophores and with the introduction of electron-donating substituents. The contributions from the resonance and coulombic components to the total energy of intramolecular interaction of the chromophores were determined. The relationship between the factors giving rise to the energy characteristics of the intramolecular interaction between the chromophores in dichromophoric systems containing a bridge structure and the factors determining the transmission of the electronic effects in the ground state is discussed in terms of orbital analysis.