Fluorescence and laser properties of D2-, C2- and D3 symmetry series oligophenylenes

The fluorescence and laser properties of ten aromatic compounds, specially chosen from the p-oligophenylenes (D-2 symmetry) or m-oligophenylenes (C-2 or D-3 symmetry) are studied experimentally (at 293 K) and quantum chemically. The quantum yields, gamma and the decay times, tau(f) of fluorescence are measured for deaerated and non-deaerated cyclohexane solutions. The oscillator strengths, f(e) of the S-0 --> S-p ((1)A --> L-1(a)) and S-0 --> S-alpha ((1)A --> L-1(b)) transitions, 0 are calculated. The lowest L-1(b), fluorescence, k(f) and intersystem crossing, k(ST), rate constants, and natural lifetimes, tau(0)(T) L-1(a) and L-3(b) (77 K) levels are determined. It is found that all p-oligophenylenes from p-terphenyl onwards are excellent, photochemically stable laser dyes although the solubility in this series decreases dramatically. On the basis of trends observed in p-oligophenylenes (D-2-series) and on the properties of the experimentally studied m-oligophenylenes of the C-2- and D-3-series, the fluorescence and laser properties of other compounds from these series are estimated/predicted. It is shown, for the first time, that m-oligophenylenes of the C-2-series, from 1,3-di(p-terphenyl)benzene will acquire fluorescence of L-1(a) --> (1)A nature and could be extremely effective laser dyes. It is also shown that m-oligophenylenes of the D-3-series, from 1,3,5-tri(p-quaterphenyl)benzene will also acquire L-1(a)--> (1)A nature fluorescence and laser ability, although this would not be as good as that of compounds in the C2-series. It is concluded that m-oligophenylenes can be used not only for passive mode locking but some may also be used as laser dyes and scintillators. The results obtained are important for various practical purposes and theoretical considerations. (C) 2002 Elsevier Science B.V. All rights reserved.