SHORT COMMUNICATION DOI: 10.1002/ejic.200800348 Spectroscopic and Computational Study on New Blue Emitting ReL(CO) 3 Cl Complexes Containing Pyridylimidazo[1,5-a]pyridine Ligands Claudio Garino, [a] Tiziana Ruiu, [a] Luca Salassa, [a] Andrea Albertino, [a] Giorgio Volpi, [a] Carlo Nervi, [a] Roberto Gobetto,* [a] and Kenneth I. Hardcastle [b] Keywords: Rhenium / X-ray structure / TDDFT / UV/Vis spectroscopy / Luminescence The structural and photophysical properties of three new ReL(CO) 3 Cl complexes (ReL1–ReL3) and their 1-(2-pyridyl)- imidazo[1,5-a]pyridine ligands, namely 3-methyl-1-(2-pyr- idyl)imidazo[1,5-a]pyridine (L1), 1-(2-pyridyl)-3-[4-(trifluoro- methyl)phenyl]imidazo[1,5-a]pyridine (L2), and 3-(4-nitro- phenyl)-1-(2-pyridyl)imidazo[1,5-a]pyridine (L3), were studied by spectroscopy, X-ray diffraction, and computa- Introduction The 1-pyridylimidazo[1,5-a]pyridine ligands recently re- ceived potential interest for optical applications, [1–3] par- ticularly in the field of OLEDs. [4,5] This class of ligands has emission in the blue region of the visible range (450– 470 nm), which is a desirable, but critical, feature in OLED technology. In a previous paper [1] we discussed the synthesis and the photophysical properties of new rhenium com- plexes containing 1-pyridylimidazo[1,5-a]pyridine ligands with electron-donor groups on a phenyl substituent. We re- port here a study on new 1-pyridylimidazo[1,5-a]pyridine ligands and their corresponding rhenium complexes (Scheme 1) having electron-withdrawing groups. Compari- son between ligands and complexes gave useful insights into their photophysical properties. [6] Time-dependent DFT (TDDFT) calculations on singlet and triplet excited Scheme 1. Schematic representation of the three ligands L1–L3 and the corresponding complexes ReL1–ReL3. [a] Dipartimento di Chimica IFM, Università di Torino, Via P. Giuria 7, 10125 Torino, Italy Fax: +39 011 6707855 E-mail: roberto.gobetto@unito.it [b] Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, USA Supporting information for this article is available on the WWW under http://www.eurjic.org/ or from the author. Eur. J. Inorg. Chem. 2008, 3587–3591 © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3587 tional methods. ReL1–ReL3 have high-energy singlet emis- sions arising from a π  π* ligand-centered state. In oxygen- free acetonitrile solutions, the complexes display dual fluo- rescence due to intense ligand-centered triplet emission. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) states [7–11] were used to estimate the nature of admixture between metal and ligand orbitals and the character of op- tically active states. Results and Discussion X-ray and Electronic Structure Crystals of ReL2 were obtained by solvent (acetonitrile) evaporation. The X-ray structure of ReL2 (Figure 1) shows the Re(CO) 3 unit to be orthogonal but rotated by 13.5° with Figure 1. X-ray structure of ReL2; displacement ellipsoids are drawn at 30% probability. Selected bond lengths (Å) and angles (°): Re1–C20 1.892(14), Re1–C21 1.897(14), Re1–C22 1.868(13), Re1–N1 2.201(10), Re1–N2 2.185(8), Re1–Cl1 2.520(3), O1–C20– Re1 177.1(10), O2–C21–Re1 178.8(11), O3–C22–Re1 175.5(9), C1– N1–Re1 124.7(8), C5–N1–Re1 117.6(7), C7–N2–Re1 135.5(7), C6– N2–Re1 114.3(6), C22–Re1–C20 88.8(5), C22–Re1–C21 86.1(5), C20–Re1–C21 87.7(5), C22–Re1–N2 99.2(4), C20–Re1–N2 99.1(4), C21–Re1–N2 171.5(4), C22–Re1–N1 91.6(4), C20–Re1–N1 174.0(4), C21–Re1–N1 98.4(4), N2–Re1–N1 74.9(3), C22–Re1–Cl1 176.7(3), C20–Re1–Cl1 93.9(4), C21–Re1–Cl1 92.0(4), N2–Re1– Cl1 82.4(2), N1–Re1–Cl1 86.0(2).