Impact of Benzannulation Site at the Diimine (N^N) Ligand on the Excited-State Properties and Reverse Saturable Absorption of Biscyclometalated Iridium(III) Complexes

Abstract

Ten biscyclometalated monocationic Ir(III) complexes were synthesized and studied to elucidate the effects of extending π-conjugation of the diimine ligand (N^N = 2,2′-bipyridine in, and 1,1′-biisoquinoline in Ir10) via benzannulation at 2,2′-bipyridine on the excited-state properties and reverse saturable absorption (RSA) of these complexes. Either a bathochromic or a hypsochromic shift of the charge-transfer absorption band and emission spectrum was observed depending on the benzannulation site at the 2,2′-bipyridine ligand. Benzannulation at the 3,4-/3′,4′-position or 5,6-/5′,6′-position of 2,2′-bipyridine ligand or at the 6,7-position of the quinoline ring on the N^N ligand caused red-shifted charge-transfer absorption band and emission band for complexes Ir2, Ir8, Ir10 vs Ir1 and Ir3 vs Ir2, while benzannulation at the 4,5-/4′,5′-position of 2,2′-bipyridine ligand or at the 7,8-position of the quinoline ring on the N^N ligand induced a blue shift of the charge-transfer absorption and emission bands for complex Ir9 vs Ir1 and Ir4 vs Ir2. However, benzannulation at the 2,2′,3,3′-position of 2,2′-bipyridine or 5,6-position of phenanthroline ligand had no impact on the energy of the chargetransfer absorption band and emission band of complexes Ir5−Ir7 compared with those of Ir1. The observed phenomenon was explained by the frontier molecular orbital (FMO) symmetry analysis. Site-dependent benzannulation also impacted the spectral feature and intensity of the triplet transient absorption spectra and lifetimes drastically. Consequently, the RSA strength of these complexes varied with a trend of Ir7 > Ir5 ≈ Ir6 ≈ Ir1 > Ir3 > Ir2 > Ir10 > Ir4 > Ir8 > Ir9 at 532 nm for 4.1 ns laser pulses.

Deep-Red Luminescence from Platinum(II) Complexes of N^N–^N-Amido Ligands with Benzannulated N-Heterocyclic Donor Arms

“…This new paradigm has been verified for 1,3-bis(2-pyridylimino)isoindolinesupported platinum chlorides, various organic emitters, 45 and phosphorescent cyclometallated Ir(III) complexes. 46 For platinum chloride complexes supported by bis(8-quinolinyl)amido ligands (e.g., 1 Me,Me ), bis(phenanthridinyl)amido ligands (3 Me,Me ) and "mixed" analogues (2 Me,Me ) that incorporate one quinoline and one phenanthridine, however, we have discovered that this model does not fully hold. 38 In these compounds, absorption and emission are not affected in the same way by benzannulation; all three complexes show isoenergetic absorption maxima, but emission from the complex with the most extended ligand π-system 3 Me,Me is blueshifted by nearly 40 nm.…”

Extending Fluorescence of meso-Aryldipyrrin Indium(III) Complexes to Near-Infrared Regions via Electron Withdrawing or π-Expansive Aryl Substituents

“…The shift in the energy of the lowest absorption band can be qualitatively predicted by the stabilization or destabilization of the frontier molecular orbitals (MOs). − As shown in Figures a and S1a, the HOMO–LUMO gap increases with the strength of the ED groups from complex 3 to 1 and decreases with the strength of the EW groups in 4 and 5 for both series-a and -b complexes, respectively. This trend is also followed by complexes 6 and 7 , showing that extended π-conjugation in the substituent groups leads to reduction of the energy gap.…”

The C–H Activation/Bidirecting Group Strategy for Selective Direct Synthesis of Diverse 1,1′-Biisoquinolines

“…Chiral 1,1′-biisoquinoline N , N ′-dioxides have shown superior catalytic capacity in asymmetric propargylation reactions . Unexpectedly, we found that the structural diversity of 1,1′-biisoquinoline ( N , N ′-dioxides) is only limited to a few symmetrical ones with −H or −Ph at the 3- and 3′-positions. − One of the possible reasons for the rare diversity of 1,1′-biisoquinoline derivatives is a tedious synthetic procedure. Another reason may be the high cost of direct functionalization of very expensive 1,1′-biisoquinoline.…”

“…Axially chiral biaryl compounds, such as the well-known BINAP, BINOL, and their diverse derivatives, have received considerable attention because they can be used as privileged ligands in asymmetric catalysis (Figure ). Their analogues, 1,1′-biisoquinolines, showed privileged coordination with metal species, and their complexes have attractive photophysical properties . Chiral 1,1′-biisoquinoline N , N ′-dioxides have shown superior catalytic capacity in asymmetric propargylation reactions .…”