Micellar effect on the photophysics of heteroleptic ruthenium(II)– phenanthrolinedisulfonato complexes Ramanathan Sangiliapillai, a Ramdass Arumugam, b Rajkumar Eswaran c * and Rajagopal Seenivasan b * ABSTRACT: Luminescent heteroleptic ruthenium(II) complexes of type RuL n X 3–n [L = 1,10-phenanthroline (phen), X = 4,7 diphenyl phenanthroline disulfonate, (dpsphen) n = 0,1,2,3] were synthesized and their photophysical properties investigated in homogeneous and cationic (CTAB), anionic (SDS) and nonionic (Triton X-100) micelles. The luminescent quantum yield and lifetime of the complexes were found to increase in the presence of micellar media and on the introduction of a disulfonate ligand into the coordination sphere. Both electrostatic and hydrophobic interactions play an important role in the micellar media. Thus, by changing the nature of the ligands and the medium, we were able to tune the photophysical properties of Ru(II) complexes. Copyright © 2015 John Wiley & Sons, Ltd. Additional supporting information may be found in the online version of this article at the publisher’s web site. Keywords: Ru(II) complexes; micelle; photophysics Introduction The study of the photophysical properties of polypyridyl complexes of ruthenium(II), [Ru(NN) 3 ] 2+ , in homogeneous and heterogeneous media has gained enormous interest because of their intriguing properties such as their strong absorption in the solar region, emission from the 3 MLCT state, moderate excited state lifetime, ability to undergo electron and energy transfer processes and high photostability (1–7). In the past two decades, a considerable amount of work has been carried out in this laboratory (8–18) on the photophysics and photoinduced electron transfer reactions of [Ru(NN) 3 ] 2+ . This work has involved introducing electron-donating and long-chain alkyl groups and electron-withdrawing -CO 2 H groups into the 4,4′-position of 2,2′-bipyridine, and introducing another nitrogen into the pyridine ring. Ligands carrying carboxylic and sulfonic acids have received special attention, because they can be anchored on a semiconductor surface to achieve efficient solar energy conversion (19–24) and to construct sensors even at the nanoscale (25–29). The photophysics and photochemistry of ru- thenium(II)–polypyridine complexes, [Ru(NN) 3 ] 2+ [NN = 2,2′- bipyridine (bpy), 1,10-phenanthroline (phen) and their derivatives], are greatly influenced by changes in the solvent and in the medium from homogeneous to microheterogeneous and hetero- geneous (30–38). Although the photophysics of Ru(II) complexes carrying the li- gands bpy and phen are interesting and important, most work on their fundamental aspects and applications have concentrated on [Ru(bpy) 3 ] 2+ and its derivatives. If we analyze the excited life- time (τ) of [Ru(bpy) 3 ] 2+ and [Ru(phen) 3 ] 2+ in different solvents, it is interesting to note that [Ru(phen) 3 ] 2+ has a higher τ value in aqueous medium (0.9 μs) than in CH 3 CN (0.4 μs). Surprisingly, the reverse is observed with [Ru(bpy) 3 ] 2+ , τ is higher in CH 3 CN (0.9 μs) than in aqueous medium (0.6 μs) (1,2). To study at the effect of changing the nature of the medium from homogeneous to microheterogeneous, through electrostatic and hydrophobic interactions, on the photophysical properties of Ru(II) complexes, we used Ru(II) complexes carrying the ligand bpy by introducing carboxylic acid and alkyl groups into the 4,4′- position of 2,2′-bipyridine (8–18). It is possible to change the hydrophobic and electrostatic interactions of [Ru(phen) 3 ] 2+ by introducing phenyl and -PhSO 3 - groups into the 4,7-position of the ligand phen. From the literature, we understand that the tris- chelated complexes [Ru(dpphen) 3 ] 2+ and [Ru(dpsphen) 3 ] 4– have extensive application as sensors when incorporated into rigid media (25–29). Although some reports (33–46) are available on the photophysics of these complexes in the presence of surfactants, a systematic study on changing the hydrophobic and electrostatic interaction of Ru(II) complexes using the ligand dpsphen has not been attempted previously. In this study, we synthesized a series of Ru(II) complexes using ligands with a change in overall charge and hydrophobicity, and studied their photophysical properties in various micellar systems. * Correspondence to: E. Rajkumar, Department of Chemistry, Madras Christian College, Chennai, Tamilnadu, India. E-mail: rajjkumar@gmail.com * S. Rajagopal, Department of Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai, Tamilnadu, India. E-mail: rajagopalseenivasan@ yahoo.com a Hajee Karutha Rowther Howdia College, Uthamapalayam, Tamilnadu, India b Department of Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai, Tamilnadu, India c Department of Chemistry, Madras Christian College, Chennai, Tamilnadu, India Luminescence 2016; 31: 30–37 Copyright © 2015 John Wiley & Sons, Ltd. Research article Received: 27 September 2014, Revised: 5 March 2015, Accepted: 5 March 2015 Published online in Wiley Online Library: 20 April 2015 (wileyonlinelibrary.com) DOI 10.1002/bio.2917 30