26 December 1997 Ž . Chemical Physics Letters 281 1997 267–271 Femtosecond transient dynamics of a heptametallic ž / HAT–ruthenium II complex. A photophysical study L. Latterini a , G. Schweitzer a , F.C. De Schryver a, ) , C. Moucheron b , A. Kirsch-De Mesmaeker b,1 a Department of Chemistry, Katholieke UniÕersiteit LeuÕen, Celestijnenlaan 200F, 3001 HeÕerlee-LeuÕen, Belgium b UniÕersite Libre de Bruxelles, Physical Organic Chemistry, CP 160 r 08 50 aÕ. F.D. RooseÕelt, 1050 Brussels, Belgium ´ Received 15 September 1997; in final form 24 October 1997 Abstract Ž .  Ž . w Ž . x 4 14q Ž A photophysical study of a heptametallic HAT–ruthenium II complex, Ru HAT Ru phen where phen s 3 26 . 1,10-phenanthroline and HAT s1,4,5,8,9,12-hexa-azatriphenylene , has been carried out using steady state and time resolved techniques. The absence of luminescence suggests that polycomplexation changes the properties of the Ru-bridging HAT luminophore inducing a decrease of the radiative rate constant and an enhancement of the non-radiative decay channel. By femtosecond transient absorption measurements a decay time of 1.9 ns has been measured for the 3 MLCT state formed upon excitation at 590 nm. Furthermore the data give information on the relaxation processes leading to the formation of the MLCT triplet state. Upon excitaton, a single decay time of 1.4 ps has been determined. The lack of faster decays, within the instrumental time resolution, may indicate that this is a relaxation time from the Frank–Condon state produced upon excitation to the triplet MLCT state. q 1997 Elsevier Science B.V. 1. Introduction During the last decade much attention has been Ž . paid to the synthesis of ruthenium II complexes with polyazaaromatic ligands and to the study of their photophysical and electrochemical properties w x 1,2 . This interest has been stimulated by attempts to design and construct multicomponent systems capa- ble of performing useful and various light induced functions, such as redox reactions. One of the area of applications for these com- pounds is based on their interactions and photoreac- ) Corresponding author. 1 Director of research at the FNRS, Belgium. tions with biological macromolecules, such as DNA w x Ž . 3,4 . It has been shown that Ru II complexes with Ž . 1,4,5,8-tetra-azaphenanthrene TAP and Ž . 1,4,5,8,9,12-hexa-azatriphenylene HAT are able to photocleave the DNA and to induce the formation of w x photoadducts with the guanine sites 5–8 . Moreover the complexes formed with a HAT ligand wchich exhibits an extended aromaticity can intercalate into the stacking of base pairs. On the other hand the use of this symmetric bridging ligand offers the possibility of designing w x supramolecular polynuclear compounds 9–11 . In this case a suitable choice of the mononuclear build- ing blocks and the bridging ligands, together with an appropriate design of the supramolecular structure 0009-2614r97r$17.00 q 1997 Elsevier Science B.V. All rights reserved. Ž . PII S0009-2614 97 01310-9