120th General Meeting of the KCS

Type Oral Presentation
Area Oral Presentation for Young Scholars in Physical Chemistry
Room No. Room 208+209+210
Time THU 10:45-:
Code PHYS.O-9
Subject Why is the photo-induced intersystem crossing of ruthenium(II) complex ultrafast and efficient?
Authors JUNWOO KIM, Taiha Joo*
Department of Chemistry, Pohang University of Science and Technology, Korea
Abstract Highly efficient photosensitizing property of transition-metal (TM) complexes has been exploited for various applications such as photovoltaic devices and photo-catalysts. For the charge generation process to occur efficiently in such systems, electron donor must be highly populated and have longer lifetime than the charge generation time. TM complexes satisfy these conditions, as their triplet states are populated by ultrafast intersystem crossing (ISC) with extremely high quantum yield. High spin-orbit coupling (SOC) constant of TM complexes leads to the ultrafast ISC, which can be measured directly by fluorescence decay. Photophysical properties of tris(2,2’-bipyridine)ruthenium(II) (RB) have been studied extensively as a typical system of TM complexes. Although, the ultrafast ISC of Ru(II) complex has been widely studied by various spectroscopic methods, it is still unclear because of its ultrafast reaction time, which is estimated to be shorter than 50 fs. To investigate the ultrafast ISC of Ru(II) complex, we studied RB and three RB analogs by time-resolved fluorescence (TRF), transient absorption (TA), and DFT/TD-DFT calculations,. Time resolutions of TF and TA were 60 and 25 fs, respectively. We measured accurate ISC times and the photo-induced coherent nuclear wave packets of all four samples, in which the vibrational motion, symmetry, and SOC are distinct. Interestingly, the calculation and experimental results classify the four complexes into two groups. The classification into the two groups and their electronic and vibrational features reveal the correlation between the ISC and nuclear motion and the details of the ultrafast ISC mechanism.
E-mail jiudiungkim@postech.ac.kr