Push-pull dyes containing malononitrile dimer as acceptor: synthesis, spectroscopy and quantum chemical calculations

The effect of structural variations of either the donor (number and positio n of methoxy groups, replacement of the aryl by Fischer's base) or the acce ptor moiety (bisacylation of the amino group, extension of the conjugated s ystem by condensation with dimethylformamide-dimethylacetale) of a series o f dyes containing malononitrile dimer as acceptor is investigated both expe rimentally and computationally. Semiempirical (AMI) and ab initio (HF/6-31G * and HF/3-21G) calculations are used for a conformational analysis of the acceptor groups and model systems thereof. Electronic excitation energies a re obtained by ZINDO, ab initio CIS/6-31+G* and time-dependent density func tional theory (TDDFT(B3LYP)/6-31+G*) computations. Inclusion of solvent eff ects is important for a reliable description of the trends observed in the experimental absorption spectra by ZINDO. Methoxyaryl, even polysubstituted , derivatives absorb at significantly shorter wavelengths than the correspo nding p-dimethylamino compounds. Replacement of the p-dimethylaminoaryl don or by Fischer's base leads to a bathochromic shift, as does the bisacylatio n of malononitrile dimer's amino group. Functionalization by condensation w ith dimethylformamide-dimethylacetale generally has only a small and irregu lar effect on absorption spectra. (C) 2001 Elsevier Science B.V. All rights reserved.