Ultrafast photophysics of iridium complexes

Iridium--Spectra;Transition metal complexes;Picosecond pulses;Phosphorescence spectroscopy

Hedley, Gordon J. ; Samuel, Ifor D. W. ; Samuel, Ifor D. W.

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Iridium--Spectra;    Transition metal complexes;    Picosecond pulses;    Phosphorescence spectroscopy;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/1981/GordonHedleyPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

This thesis presents ultrafast photophysical measurements on a number ofphosphorescent iridium complexes and establishes relationships between therelaxation rates and the vibrational properties of the material.When ultrafast luminescence is measured on the peak of the phosphorescencespectrum and on its red-side, 230 fs and 3 ps decay time constants were observedin all materials studied, and this was attributed to population redistributionamongst the three electronic substates of the lowest triplet metal-ligand chargetransfer (MLCT) state.The observation of luminescence at higher values of energy embodied ultrafastdissipation of excess energy by intramolecular vibrational redistribution (IVR)and it was found that the dissipation channels and rate of IVR could be modifiedby chemical modification of the emitting molecule. This was tested in two ways.Firstly by adding electronically inactive dendrons to the core, an increase in thepreference for dissipation of excess energy by IVR rather than by picosecondcooling to the solvent molecules was found, but this did not change the rate ofIVR. The second method of testing was by fusing a phenyl moiety directly ontothe ligand, this both increased the rate of IVR and also the preference fordissipation by it rather than by picosecond cooling.Fluorescence was recorded in an iridium complex for the first time and a decaytime constant of 65 fs was found, thus allowing a direct observation of intersystemcrossing (ISC) to be made.In a deep red emitting iridium complex internal conversion (IC) and ISC wereobserved and the factors controlling their time constants deduced. IC was found to occur by dissipation of excess energy by IVR. The rate of IC was found to bedependent on the amount of vibrational energy stored in the molecule, with IC fast(< 45 fs) when < 0.6 eV of energy is stored and slower (~ 70 fs) when the value is> 0.6 eV. The rate of ISC agreed with these findings, indicating that the veryprocess of ISC may be thought of as closely analogous to that of IC given thestrongly spin-mixed nature of the singlet and triplet MLCT states.