π-conjugation and charge polarization in fluorene-dibenzothiophene-S,S-dioxide co-oligomers by Raman spectroscopy and quantum chemistry

The Raman spectra of a series of fluorine (F)/dibenzothiophene-S,S-dioxide co-oligomers (S) of different length and alternation sequences in their backbones (FSF, FFSFF, FSFSF, and FASAF; A is the -C=C- bridge) have been recorded and simulated theoretically. It is shown that Raman spectroscopy is useful to probe pi conjugation and ground state electron polarization in these molecules, phenomena directly related with the existence of intramolecular charge-transfer processes owing to the combination of electron donor (fluorene) and acceptor (dibenzothiophene-S,S-dioxide) groups. Their geometric, electronic, and vibrational properties have been studied by density functional theory B3LYP/6-311G(2d,p) quantum chemical calculations and compared with those for fluorene homooligomers. Comparative studies in solution/solid/melted phase led to the conclusion that the Raman wavenumbers are also sensitive to intermolecular interactions. (C) 2011 American Institute of Physics. [doi:10.1063/1.3526487]