Theoretical interpretation of electronic absorption and emission transitions in 9-acridinones A. Bouz ˙yk a , L. Jo ´z ´wiak a , A.Yu. Kolendo b , J. Bl  az ˙ejowski a,  a Department of Chemistry, University of Gdan ´sk, Sobieskiego 18, 80-952 Gdan ´sk, Poland b Department of Chemistry, Kyiv Taras Shevchenko National University, 01033 Kiev, Volodymyrska 64, Ukraine Received 4 January 2002; received in revised form 10 May 2002; accepted 13 May 2002 Abstract Stationary absorption, fluorescence excitation and fluorescence spectra for 9(10H )-acridinone, 9(10-methyl)- acridinone, 2-methyl-9(10-methyl)-acridinone, 2-nitro-9(10-methyl)-acridinone, 9(10-ethyl)-acridinone and 9(10-phen- yl)-acridinone dissolved in 1,4-dioxane, methyl alcohol or acetonitrile, as well as the available spectral characteristics reported by others were compared with those predicted theoretically at the semi-empirical PM3/CI (including the solvent effect within the COSMO model) or PM3/S levels of theory, in order to interpret spectral features of the compounds, i.e. the energies and probabilities of S 0 0/S n ,S 0 0/T 1 ,T 1 0/T 2 ,S 1 0/S 0 ,T 1 0/S 0 and S 1 0/T 1 transitions. Calculations at the PM3 and PM3/CI levels of theory enabled the structural changes accompanying S 0 0/S 1 ,S 1 0/T 1 and T 1 0/S 0 transitions to be investigated; they yielded, moreover, basic physicochemical characteristics of the molecules in the ground and excited electronic states. Theoretically predicted dipole moments and charge distributions in the S 0 ,S 1 and T 1 states provided further insight into the nature of electronic transitions in 9-acridinones. The predicted characteristics correlate quite well with the available experimental ones, thus providing confirmation of the utility of theory in predicting the features of electronically excited molecules and interpreting the electronic transitions occurring in them. # 2002 Elsevier Science B.V. All rights reserved. Keywords: 9-acridinones; Electronic absorption and emission spectra (transitions); Theory; Interpretation; Features of excited states 1. Introduction 9-Acridinones are heterocyclic compounds con- taining secondary or tertiary amino and keto fragments within the ring system that confer on these molecules the ability to interact specifically with other molecules from their immediate sur- roundings [1,2]. These compounds are therefore convenient models for investigating the features of entities that are at once aromatic amines and ketones. Of particular interest is the ability of 9- acridinones to absorb UV  /VIS radiation and emit it efficiently in the short-wavelength visible region. The absorption of gaseous 9(10H )-acridinone and 9(10-methyl)-acridinone [3], the absorption of  Corresponding author. Tel.:  /48-58-3450331; fax:  /48- 58-3410357 E-mail address: bla@chemik.chem.univ.gda.pl (J. Bl  az ˙ejowski). Spectrochimica Acta Part A 59 (2003) 543  /558 www.elsevier.com/locate/saa 1386-1425/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S1386-1425(02)00195-6