Luminescent Cyclometalated Iridium Complexes Synthesis Photophysical and Computational Investigations

Abstract

The thesis entitled Luminescent Cyclometalated Iridium Complexes: Synthesis, Photophysical and Computational Investigations is primarily an effort towards the development of cyclometalated iridium complexes tuning their electronic enviourment toward their photophysical properties. Here, we developed cyclometalated iridium complexes {[1](PF6) [16](PF6)} using benzimidazole as C^N chelating ligand in combination with different N^N coordinating ancillary ligand framework and exploration of their structural, photophysical and electrochemical aspects. The characterizations of the complexes were carried out using various analytical techniques. Apart from showing the expected electrochemical behavior, the complexes display distorted octahedral geometry around the iridium center. The variation of alkyl chain length at the benzimidazole unit within the complexes {[1](PF6) [5](PF6)} results in a shift in the emission maxima from 570 nm to 640 nm and also results in a moderately longer emission lifetime (and#964; = 766 ns) for [5](PF6) in water. The longer excited-state lifetime could possibly be due to the T1 state with 3MLLCT character, as observed from TDDFT analysis of the triplet state. The emission lifetime gets further enhanced in aqueous medium {and#964; = 1900 ns for [8](PF6)} when semi-flexible and#960;-conjugated dppz-based N^N chelating ligands are introduced in the complexes {[6](PF6) [9](PF6)}. The TDDFT and spin density analysis of the triplet state reveal that the T1 state of [8](PF6) is 3LC character which could be responsible for displaying the longer excited state lifetime. The addition of fluorine (F) in phenyl ring in the complexes [10](PF6) and [12](PF6) stabilizes the HOMO and causes blue shift of the emission maxima, whereas the HOMO gets destabilized while phenyl ring is replaced by thiophene unit in complexes [11](PF6) and [13](PF6) which give rise to red shift of both the absorption and emission maxima.