The Pi‐Nature of Methyl Obtained by the Natural Bond Orbital Method: Orbital‐Based Rationalizations of Site‐Dependent Substitution Effects on Fine Color‐Tuning of Luminescence

• DOI: 10.1002/jccs.201200354
• Publication Date: 2012-09-17T09:28:49Z
• Authors: Wei‐Lin Su; Cheng‐Chi Wang; Shao‐Pin Wang
• Keywords: HOMO/LUMO; Natural bond orbital; Antibonding molecular orbital; Non-bonding orbital; Molecular orbital diagram

Abstract Both C‐H bonding and antibonding (σ CH σ* ) of a methyl group would contribute to the highest occupied or lowest unoccupied molecular orbitals (HOMO LUMO) in methylated derivatives Ir(ppz) 2 3 iq (ppz = 1‐phenylpyrazole 3iq isoquinoline‐3‐carboxylate). This is found by analysis HOMO (or formed linear combination bond using natural orbital (NBO) method. The elevated level uniformly for each derivative, indicating σ ‐destabilization outweighs ‐stabilization. To broaden HOMO‐LUMO gap, methylation at carbon having smaller contribution and/or larger LUMO suggested.