282
D. Escudero
lowest adiabatic ES. In conclusion, the switch from dual photoluminescence to sole
3 MLCT-like emission from 298 to 77 K roots on the possibility to attain thermally
equilibrated ES at room temperature.
4 Conclusion and Perspectives
One can easily recognize that the photophysical and photochemical properties of
TMCs are more chameleonic than those of organic compounds [101]. The significant
experimental and theoretical activity that has emerged in this field during the past
years has permitted to underline the complexity of the ES dynamics in TMCs. As
a consequence of the gained understanding, early empirical concepts developed for
the rationalization of spectral features, lifetimes, ES kinetics, and photoluminescence
efficiencies are nowadays a matter of debate in the community. Indeed, the use of
simple qualitative rules, such as, El-Sayed- [102] and Kasha- [8] rules, as well as the
energy gap law [31], should cautiously be done for TMCs, as these empirical laws
can often lead to erroneous predictions of the preferred photochemical outcomes.
Importantly, all these new insights would have not been possible without the strong
synergy between experimental and theoretical and computational efforts. Throughout
this chapter, the advances and the numerous difficulties that are still present in the
field have been highlighted and will not be repeated here. Obviously, the forthcoming
theoretical/computational developments in quantum chemical methods for the ES,
ES decay rate formalisms, and ES reaction dynamic methods should tackle the current
deficiencies to model the photodeactivation channels of TMCs.
References
1. Daniel C, Gourlaouen C (2017) Chemical bonding alteration upon electronic excitation in
transition metal complexes. Coord Chem Rev 344:131–149
2. Daniel C (2015) Photochemistry and photophysics of transition metal complexes: quantum
chemistry. Coord Chem Rev 282–283:19–32
3. González L, Escudero D, Serrano-Andrés L (2012) Progress and challenges in the calculation
of electronic excited states. Chem Phys Chem 13:28–51
4. Stufkens DJ, Vlˇ cek A (1998) Ligand-dependent excited state behavior of Re(I) and Ru(II)
carbonyl-diimine complexes. Coord Chem Rev 177:127–179
5. Mai S, Plasser F, Dorn J, Fumanal M, Daniel C, González L (2018) Quantitative wave function
analysis for excited states of transition metal complexes. Coord Chem Rev 361:74–97
6. Le Bahers T, Adamo C, Ciofini I (2011) A qualitative index of spatial extent in charge-transfer
excitations. J Chem Theory Comput 7:2498–2506
7. Jacquemin D, Le Bahers T, Adamo C, Ciofini I (2012) What is the “best” atomic charge model
to describe through-space charge-transfer excitations? Phys Chem Chem Phys 14:5383–5388
8. Kasha M (1950) Characterization of electronic transitions in complex molecules. Discuss
Faraday Soc 9:14–19
9. Penfold TJ, Gindensperger E, Daniel C, Marian CM (2018) Spin-vibronic mechanism for
intersystem crossing. Chem Rev 118:6975–7025
D. Escudero
lowest adiabatic ES. In conclusion, the switch from dual photoluminescence to sole
3 MLCT-like emission from 298 to 77 K roots on the possibility to attain thermally
equilibrated ES at room temperature.
4 Conclusion and Perspectives
One can easily recognize that the photophysical and photochemical properties of
TMCs are more chameleonic than those of organic compounds [101]. The significant
experimental and theoretical activity that has emerged in this field during the past
years has permitted to underline the complexity of the ES dynamics in TMCs. As
a consequence of the gained understanding, early empirical concepts developed for
the rationalization of spectral features, lifetimes, ES kinetics, and photoluminescence
efficiencies are nowadays a matter of debate in the community. Indeed, the use of
simple qualitative rules, such as, El-Sayed- [102] and Kasha- [8] rules, as well as the
energy gap law [31], should cautiously be done for TMCs, as these empirical laws
can often lead to erroneous predictions of the preferred photochemical outcomes.
Importantly, all these new insights would have not been possible without the strong
synergy between experimental and theoretical and computational efforts. Throughout
this chapter, the advances and the numerous difficulties that are still present in the
field have been highlighted and will not be repeated here. Obviously, the forthcoming
theoretical/computational developments in quantum chemical methods for the ES,
ES decay rate formalisms, and ES reaction dynamic methods should tackle the current
deficiencies to model the photodeactivation channels of TMCs.
References
1. Daniel C, Gourlaouen C (2017) Chemical bonding alteration upon electronic excitation in
transition metal complexes. Coord Chem Rev 344:131–149
2. Daniel C (2015) Photochemistry and photophysics of transition metal complexes: quantum
chemistry. Coord Chem Rev 282–283:19–32
3. González L, Escudero D, Serrano-Andrés L (2012) Progress and challenges in the calculation
of electronic excited states. Chem Phys Chem 13:28–51
4. Stufkens DJ, Vlˇ cek A (1998) Ligand-dependent excited state behavior of Re(I) and Ru(II)
carbonyl-diimine complexes. Coord Chem Rev 177:127–179
5. Mai S, Plasser F, Dorn J, Fumanal M, Daniel C, González L (2018) Quantitative wave function
analysis for excited states of transition metal complexes. Coord Chem Rev 361:74–97
6. Le Bahers T, Adamo C, Ciofini I (2011) A qualitative index of spatial extent in charge-transfer
excitations. J Chem Theory Comput 7:2498–2506
7. Jacquemin D, Le Bahers T, Adamo C, Ciofini I (2012) What is the “best” atomic charge model
to describe through-space charge-transfer excitations? Phys Chem Chem Phys 14:5383–5388
8. Kasha M (1950) Characterization of electronic transitions in complex molecules. Discuss
Faraday Soc 9:14–19
9. Penfold TJ, Gindensperger E, Daniel C, Marian CM (2018) Spin-vibronic mechanism for
intersystem crossing. Chem Rev 118:6975–7025