Exciplex Formation of rac- and meso-2,4-Di(N-carbazolyl)pentane with m-Dicyanobenzene. Model Systems for Fluorescence Quenching in Poly(N-vinylcarbazole)

N-Isopropylcarbazole, trans-1,2-di(N-carbazolyl)cyclobutane, and the two diastereomers of 2,4-di(N-carbazolyl)pentane, model compounds for poly(N-vinylcarbazole), were quenched with m-dicyanobenzene. The fluorescence spectra of N-isopropylcarbazole and trans-1,2-di(N-carbazolyl)cyclobutane in the presence of m-dicyanobenzene show a new emission band with a maximum at 410 nm. This band was assigned to the emission of a normal exciplex. The fluorescence spectra of meso- and rac-2,4-di(N-carbazolyl)pentane, model compounds respectively for iso- and syndiotactic sequences in poly(N-vinylcarbazole), in the presence of m-dicyanobenzene both show a new emission band, with a maximum at 510 and 460 nm, respectively. These bands, more bathochromic than that of the normal exciplex, are assigned to the emission of a triple excited complex formed between the respective excimers and a m-dicyanobenzene acceptor molecule. The excimer formed by the meso compound (total spatial overlap of carbazole chromophores) has better donor properties than the excimer formed by the racemic compound (partial spatial overlap of the carbazole chromophores).