Fluorescence and laser properties of D 2 -, C 2 - and D 3 symmetry series oligophenylenes R. Mabbs a, *, N. Nijegorodov b , W.S. Downey b a Chemistry Department, University of Botswana, Private Bag 0022, Gaborone, Botswana b Physics Department, University of Botswana, Private Bag 0022, Gaborone, Botswana Received 3 December 2001; received in revised form 9 September 2002; accepted 13 September 2002 Abstract 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, g and the decay times, t f of fluorescence are measured for deaerated and non-deaerated cyclohexane solutions. The oscillator strengths, f e of the S 0 0/S p ( 1 A 0/ 1 L a ) and S 0 0/S a ( 1 A 0/ 1 L b ) transitions, fluorescence, k f and intersystem crossing, k ST , rate constants, and natural lifetimes, t 0 T are calculated. The lowest 1 L b , 1 L a and 3 L 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 1 L a 0/ 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 1 L a 0/ 1 A nature fluorescence and laser ability, although this would not be as good as that of compounds in the C 2 -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. # 2002 Elsevier Science B.V. All rights reserved. Keywords: p -Oligophenylenes; m -Oligophenylenes; Fluorescence properties; Laser properties 1. Introduction The possibility of using p -oligophenylenes and their derivatives as active media in dye lasers, producing coherent emission in the near ultra vio- let, has been shown in [1,2] and more recently in [3  /5]. It has also been pointed out that some m - oligophenylenes, while unable to show laser ac- * Corresponding author. Present address: Department of Chemistry, The University of Arizona, Tucson, AZ 85721-0041, USA. E-mail address: mabbsr@u.arizona.edu (R. Mabbs). Spectrochimica Acta Part A 59 (2003) 1329  /1339 www.elsevier.com/locate/saa 1386-1425/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S1386-1425(02)00329-3