In the current work,
comprehensive photophysical and electrochemical
studies were performed for eight rhenium(I) complexes incorporating
2,2′:6′,2″-terpyridine (terpy) and 2,6-bis(pyrazin-2-yl)pyridine
(dppy) with appended 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl, and
1-pyrenyl groups. Naphthyl and phenanthrenyl substituents marginally
affected the energy of the MLCT absorption and emission bands, signaling
a weak electronic coupling of the appended aryl group with the Re(I)
center. The triplet MLCT state in these complexes is so low lying
relative to the triplet
3
IL
aryl
that the thermal
population of the triplet excited state delocalized on the organic
chromophore is ineffective. The attachment of the electron-rich pyrenyl
group resulted in a noticeable red shift and a significant increase
in molar absorption coefficients of the lowest energy absorption of
the resulting Re(I) complexes due to the contribution of intraligand
charge-transfer (ILCT) transitions occurring from the pyrenyl substituent
to the terpy/dppy core. At 77 K, the excited states of [ReCl(CO)
3
(L
n
-κ
2
N
)] with 1-pyrenyl-functionalized ligands were found to
have predominant
3
IL
pyrene
/
3
ILCT
pyrene→terpy
character. The
3
IL/
3
ILCT nature of the lowest energy excited state of [ReCl(CO)
3
(4′-(1-pyrenyl)-terpy-κ
2
N
)] was also evidenced by nanosecond transient absorption and time-resolved
emission spectroscopy. Enhanced room-temperature emission lifetimes
of the complexes [ReCl(CO)
3
(L
n
-κ
2
N
)] with 1-pyrenyl-substituted
ligands are indicative of the thermal activation between
3
MLCT and
3
IL/
3
ILCT excited states. Deactivation
pathways occurring upon light excitation in [ReCl(CO)
3
(4′-(1-naphthyl)-terpy-κ
2
N
)] and [ReCl(CO)
3
(4′-(1-pyrenyl)-terpy-κ
2
N
)] were determined by femtosecond transient
absorption studies.
In this work, the
structure–property relationship was investigated
for a series of Re(I) carbonyls [ReCl(CO)3(R-terpy-κ2N)], [ReCl(CO)3(R-dtpy-κ2N)], and [ReCl(CO)3(R-dppy-κ2N)]. The studied compounds bear 2,2′:6′,2″-terpyridines
(R-terpy), 2,6-di(thiazol-2-yl)pyridines (R-dtpy), and 2,6-di(pyrazin-2-yl)pyridines (R-dppy) functionalized with strongly electron-donating cyclic (piperidine
and morpholine) and acyclic (dimethylamine, diphenylamine) amine donor
attached to the central pyridine ring of the triimine skeleton via
phenylene linkage. Their thermal properties were evaluated using DSC.
The ground- and excited-state properties of these systems were elucidated
with electrochemistry, absorption and emission spectroscopy, and density-functional
theory (DFT)-based calculations. The terpy skeleton
was found to efficiently stabilize the LUMO orbital, as manifested
by the most negative reduction potentials for Re(I) terpyridine complexes
and significant blue-shift of the absorption and emission of [ReCl(CO)3(R-terpy-κ2N)] in relation
to those of Re(I) carbonyls bearing dtpy- and dppy-based ligands. Substitution of the triimines with amine
substituents resulted in participation of intraligand charge-transfer
(ILCT) transitions, and it was found to be beneficial for hole-transport
properties of the Re(I) carbonyls. The constructed nondoped and doped
single layer diodes based on Re(I) complexes emitted red light with
various intensity.
We demonstrate that controlled assembly of eukaryotic photosystem I with its associated light harvesting antenna complex (PSI-LHCI) on plasmonically active silver nanowires (AgNWs) substantially improves the optical functionality of such a novel biohybrid nanostructure. By comparing fluorescence intensities measured for PSI-LHCI complex randomly oriented on AgNWs and the results obtained for the PSI-LHCI/cytochrome c (cyt c) bioconjugate with AgNWs we conclude that the specific binding of photosynthetic complexes with defined uniform orientation yields selective excitation of a pool of chlorophyll (Chl) molecules that are otherwise almost non-absorbing. This is remarkable, as this study shows for the first time that plasmonic excitations in metallic nanostructures can not only be used to enhance native absorption of photosynthetic pigments, but also - by employing cyt c as the conjugation cofactor - to activate the specific Chl pools as the absorbing sites only when the uniform and well-defined orientation of PSI-LHCI with respect to plasmonic nanostructures is achieved. As absorption of PSI alone is comparatively low, our approach lends itself as an innovative approach to outperform the reported-to-date biohybrid devices with respect to solar energy conversion.
We demonstrate that oriented assembly of red algal photosystem I reaction centers on a plasmonically active Silver Island Film leads to strong enhancement of both photocurrent and fluorescence intensity.
Photon avalanche (PA) is a highly nonlinear mode of upconversion that is characterized by 100–1000‐fold increase in luminescence intensity upon minute increments of pumping power. The practical realization of numerous possible nano‐bio‐technology applications utilizing the PA phenomenon will require information on its susceptibility to the material volume and surface. Here, these parameters are investigated via experimental and theoretical PA. The two‐color, highly nonlinear PA emission at 475 and 800 nm is clearly observed in bulk single crystal, individual microcrystals, and ensembles of colloidal core and core–shell nanoparticles of LiYF4 host doped with either 3 or 8% of thulium ions. The properties of PA emission, such as PA nonlinearity, PA gain, PA intensity, and luminescence kinetics in these materials show dependence on crystal volume and surface quenching. Theoretical simulations provide understanding of key physical processes that influence PA performance. Moreover, photon avalanche single beam super‐resolution imaging is realized for the first time in 3% Tm3+ doped LiYF4 core–shell nanoparticles. The obtained insights and predictions form a solid background for further development and applications of new optimized PA materials.
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