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Cyclometalated Ir III Complexes with Substituted 1,10‐Phenanthrolines: A New Class of Efficient Cationic Organometallic Second‐Order NLO Chromophores
Author(s) -
Valore Adriana,
Cariati Elena,
Dragonetti Claudia,
Righetto Stefania,
Roberto Dominique,
Ugo Renato,
De Angelis Filippo,
Fantacci Simona,
Sgamellotti Antonio,
Macchioni Alceo,
Zuccaccia Daniele
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902788
Subject(s) - chemistry , cationic polymerization , chromophore , thiazole , time dependent density functional theory , crystallography , delocalized electron , stereochemistry , medicinal chemistry , photochemistry , density functional theory , computational chemistry , polymer chemistry , organic chemistry
Cyclometalated cationic Ir III complexes with substituted 1,10‐phenanthrolines (1,10‐phen), such as [Ir(ppy) 2 (5‐R‐1,10‐phen)]Y (ppy=cyclometalated 2‐phenylpyridine; R=NO 2 , H, Me, NMe 2 ; Y − =PF 6 − , C 12 H 25 SO 3 − , I − ) and [Ir(ppy) 2 (4‐R,7‐R‐1,10‐phen)]Y (R=Me, Ph) are characterized by a significant second‐order optical non linearity (measured by the electrical field induced second harmonic generation (EFISH) technique). This nonlinearity is controlled by MLCT processes from the cyclometalated Ir III , acting as a donor push system, to π* orbitals of the phenanthroline, acting as an acceptor pull system. Substitution of cyclometalated 2‐phenylpyridine by the more π delocalized 2‐phenylquinoline (pq) or benzo[ h ]quinoline (bzq) or by the sulfur‐containing 4,5‐diphenyl‐2‐methyl‐thiazole (dpmf) does not significantly affect the μβ absolute value, which instead is affected by the nature of the R substituents on the phenanthroline, the higher value being associated with the electron‐withdrawing NO 2 group. By using a combined experimental (the EFISH technique and 1 H and 19 F PGSE NMR spectroscopy) and theoretical (DFT, time‐dependent‐DFT (TDDFT), sum over states (SOS) approach) investigation, evidence is obtained that ion pairing, which is controlled by the nature of the counterion and by the concentration, may significantly affect the μβ values of these cationic NLO chromophores. In CH 2 Cl 2 , concentration‐dependent high absolute values of μβ are obtained for [Ir(ppy) 2 (5‐NO 2 ‐1,10‐phen)]Y if Y is a weakly interacting anion, such as PF 6 − , whereas with a counterion, such as C 12 H 25 SO 3 − or I − , which form tight ion‐pairs, the absolute value of μβ is lower and quite independent of the concentration. This μβ trend is partially due to the perturbation of the counterion on the LUMO π* levels of the phenanthroline. The correlation between the μβ value and dilution shows that the effect of concentration is a factor that must be taken into careful consideration.