FULL PAPER DOI:10.1002/ejic.201402222 Aggregation-Induced Emission Activity in Iridium(III) Diimine Complexes: Investigations of Their Vapochromic Properties Parvej Alam, [a] Maheswararao Karanam, [b] Debashree Bandyopadhyay,* [c] Angshuman Roy Choudhury,* [b] and Inamur Rahaman Laskar* [a] Keywords: Luminescence / Iridium / Nitrogen heterocycles / Density functional calculations Two iridium(III) diimine complexes [mono(1,10-phenanthrol- ine)bis(triphenylphosphine)(dihydrido)iridium(III) hexa- fluorophosphate (1) and mono(1,10-phenanthroline)bis(tri- phenylphosphine)(hydrido)(chloro)iridium(III) hexafluoro- phosphate (2)] have been synthesized from a single two-step reaction. The structures of 1 and 2 both adopt distorted octa- hedral geometries, as established by single-crystal X-ray dif- fraction. The complexes, upon irradiation with UV light at 365 nm, emit faint light in solution and bright light in the solid state. The ground- and excited-state properties of these complexes were investigated through density functional theory (DFT) and time-dependent DFT calculations. The cal- culated energies for the transitions from the ground state to the singlet and triplet excited states were close to those de- Introduction Luminescent materials are widely used as vapolumines- cent materials to detect volatile organic compounds (VOCs) in the environment or workplace. [1–13] These materials usu- ally show changes in emission intensity or wavelength when exposed to specific VOCs. This variation in luminescence properties triggered by the presence of VOCs results in changes in, for example, metallophilic interactions, [14] hydrogen bonding, [15] solvent–metal bonds, [16] and aromatic [a] Department of Chemistry, Birla Institute of Technology and Science, Pilani Campus, Pilani, Rajasthan, India E-mail: ir_laskar@bits-pilani.ac.in http://www.bits-pilani.ac.in/Pilani/index.aspx [b] Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER), Mohali, Sector 81, S. A. S. Nagar, Manauli PO, Mohali, Punjab 140306, India angshuman@iisermohali.ac.in http://www.iisermohali.ac.in/ [c] Department of Biological Sciences, Birla Institute of Technology and Sciences, Hyderabad Campus, Jawahar Nagar, Shameerpet Mandal, Hyderabad, Andhra Pradesh 50078, India banerjee@yahoo.com http://www.bits-pilani.ac.in/hyderabat/ Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201402222. Eur. J. Inorg. Chem. 2014, 3710–3719 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3710 termined from the experimental absorption and emission. Their molecular orbitals were also exploited to compute the ground-state dipole moments and redox potentials. Several experiments were performed to demonstrate the “aggrega- tion-induced emission” (AIE) activity of these complexes. AIE was triggered by the restricted intramolecular rotation of the rotating units (phenyls in triphenyphosphines) in these molecules in the solid state. The solid thin films of 1 and 2 exhibit solvent-polarity-dependent vapour-responsive emis- sion properties (vapoluminescent). The rationale for the dif- ferent emission behavior in the solid state has been thor- oughly investigated. The packing diagrams of 1 and 2 show that there is enough space available to accommodate small organic solvent molecules inside the crystal lattices. π–π stacking interactions. [17] There have been many reports of organometallic and coordination complexes of Ru, [18] Sn, [19] Pt/Pd, [20] Cu, [21] Zn, [22] Au, [23] Ag, [24] and Re/Co [25] that have been used in vapor-responsive luminescent materi- als. However, the most extensive studies have been carried out with platinum(II) and gold(I). Metallophilic interac- tions between Pt II or Au I are either disrupted or enhanced upon interaction with VOCs, thereby altering the gap be- tween the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO), thus leading to distinct changes in the emission or absorption spectra. In comparison with other luminescent metallic complexes, several distinct advantages have been observed with cyclometalated iridium(III) complexes, for example, superior quantum efficiencies, easy tunability of light emis- sion wavelength, higher thermal and electrochemical sta- bility, and straightforward synthetic routes in comparison with other analogues. [26] Notwithstanding, reports on emit- ting iridium(III) complexes as vapoluminescent materials are very limited. [12] Recently we reported [27] a one-pot synthetic route to ag- gregation-induced-emission (AIE)-active monocyclometal- ated iridium(III) complexes and their easy tunability throughout the visible range within the common framework of an iridium(III) complex. [28] AIE [29–32] is an anomalistic