SEMIEMPIRICAL CHARACTERIZATION OF SUBSTITUTED BIS-PYRAZOLOPYRIDINES AS NEW BULKY ELECTRON DONOR-ACCEPTOR SYSTEMS IN THEIR ELECTRONIC GROUND-STATE

Geometries, conformational energies and activation barriers for rotati ons about the single bonds connecting the various subunits of a new cl ass of bulky electron donor-acceptor systems derived from the bis-pyra zolopyridine chromophore are characterized for several representatives by semiempirical methods (AMI and PM3). For the dimethylaminophenyl d erivative DMA-DMPP -1,7-diphenyl-bis-pyrazolo-[3,4-b;4',3'e]pyridine) dual fluorescence was observed in polar, protic solvents and was discu ssed in the context of;the TICT (twisted intramolecular charge transfe r) hypothesis, first formulated to explain dual fluorescence of 4-(N,N -dimethylamino)benzonitrile (DMABN), Besides the parent H-DMPP molecul e, derivatives substituted with different donor or acceptor groups wer e compared with respect to their optimum ground-state geometries, (C) 1997 Elsevier Science B.V.