XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
14
K–3
Probing radical and nitrene intermediates in narrowband UV-induced
photoreactions in cryogenic inert matrices
Rui Fausto
1
1
CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
e-mail: rfausto@ci.uc.pt
Radical and nitrene intermediates play a fundamental role in chemical reactivity. However,
their capture and characterization, as well as the precise description of their reactivity, pose
always enormous challenges to investigation.
Matrix isolation is a powerful tool to study short-living species, and is nowadays a mature
technique suitable to address complex problems of chemical reactivity involving reaction
intermediates. In fact, when used together with contemporary computational methods of
quantum chemistry and up-to-date narrowband tunable light sources, matrix isolation may be
used very successfully for investigation of elusive reaction intermediates, in a very elegant and
direct way.
In this tall, I will describe a series of possible strategies for research on the structures and
reactivity of radical and nitrene intermediates participating in photochemical processes, based on
the conjugated use of theoretical methods and matrix isolation coupled with spectroscopic
probing. Recent results on the photochemistry of phenols and thiophenols, in which radicals
play a prominent role, and of several types of nitrene precursors, like isoxazoles, azides and
tetrazoles, will be presented. In these studies, narrowband tunable light sources were used to
selectively excite the different species formed along the targeted reactions, allowing the
unequivocal identification of the transient radicals and nitrenes formed along these processes,
their structural characterization and the evaluation of their specific reactivity. On the way, the
first direct observation of a tunneling reaction involving a nitrene, and the production of several
rare high-energy species resulting from photochemical processes where radical and nitrene
intermediates play central mechanistic roles will be reported.
Acknowledgment
Present and past members of the Laboratory for Molecular Cryospectroscopy and Biospectroscopy,
Coimbra, Portugal, and research partners from other laboratories, who have contributed to the studies
addressed in this talk, are acknowledged. I thank also the Portuguese Science Foundation (FCT) for
financial support (Project PTDC/QEQ-QFI/3284/2014 – POCI-01-0145-FEDER-016617, also funded by
FEDER/COMPETE 2020-UE). The Coimbra Chemistry Centre (CQC) is supported by FCT, through the
project UI0313/QUI/2013, also co-funded by FEDER/COMPETE 2020-EU.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
15
K–4
Generating long-lived charge-separated excited states
from blended organic, inorganic chromophore systems:
a spectroscopic and computational study
Keith C. Gordon
1
1
University of Otago, Department of Chemistry, Union Place West, Dunedin, New Zeland,
e-mail: keith.gordon@otago.ac.nz
Donor-acceptor interactions are critical in many light driven systems such as photocatalysts
or photovoltaic materials. In particular many promising bulk heterojunction polymer solar cell
materials rely on donor-acceptor interactions overlaid with H-bonding interactions. Often
density functional theory (DFT) is used provide predictive insight into polymer design. We
have undertaken a systematic study of simple donor-acceptor units that show the fragility of
DFT in being effective at predicting optical properties. With this in mind we have designed and
made a series of metal-based complexes that incorporate blended organic (intra-ligand charge-
transfer, ILCT, units) and inorganic (metal-dipyridophenazine metal-to-ligand charge-transfer,
MLCT, units) to create charge-separated states with up to 6 microsecond lifetimes in solution at
room temperature (Fig. 1). The nature of the donor-acceptor interaction on both the ground and
excited electronic states has been studied as a function of donor-acceptor distance, angle and
linker group. We have used resonance Raman spectroscopy to characterise the ground state
electronic transitions and time-resolved infrared and resonance Raman spectroscopy to
characterise the excited states. We find that the ground state properties are strongly correlated
with linker and distance as might be expected. However the excited state properties are
dominated by driving force effects and are not a function of the linker.
S
N
N
N
N
N
N
N
N
N
Cl(CO)
3
Re
N
N
N
N
donor
-NPh
2
-thio-TPA
-thio-TPA
-TPA
-Ph-TPA
-Ph
2
-TPA
[Re(CO)
3
Cl(dppz-donor)]
Fig. 1. Selection of compounds used in this study.
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