Effects of molecular geometry on the efficiency of intramolecular charge transfer-based luminescence in -carboranyl-substituted 1-phenanthro[9,10-]imidazoles
Herein, we compared the optical properties of four compounds with an o -carborane cage linked to 1 H -phenanthro[9,10- d ]imidazole at the ortho - ( o PC ), meta - ( m PC ), or para -position ( p PC ) of the 2-phenyl ring or at the C2-position ( PC ) of the phenanthroimidazole moiety. In the solid s...
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| Published in | Inorganic chemistry frontiers Vol. 9; no. 3; pp. 51 - 513 |
|---|---|
| Main Authors | , , , , , , |
| Format | Journal Article |
| Published |
01.02.2022
|
| Online Access | Get full text |
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| Summary: | Herein, we compared the optical properties of four compounds with an
o
-carborane cage linked to 1
H
-phenanthro[9,10-
d
]imidazole at the
ortho
- (
o
PC
),
meta
- (
m
PC
), or
para
-position (
p
PC
) of the 2-phenyl ring or at the C2-position (
PC
) of the phenanthroimidazole moiety. In the solid state,
p
PC
and
PC
exhibited intense intramolecular charge transfer (ICT)-based emission centred at ∼560 nm, while
o
PC
and
m
PC
exhibited dual emission in high-energy (
λ
em
385 nm) and low-energy (
λ
em
580 nm) regions due to a locally excited transition and ICT-based emission, respectively. Thus, the quantum efficiency and radiative decay constant of ICT-based emission in the film state were much higher for
p
PC
and
PC
than for
o
PC
and
m
PC
. Analysis of solid-state molecular structure revealed a notable geometric difference between these two pairs, showing that the C-C bond axis of the
o
-carborane was orthogonal to the plane of the appended aromatic group for
p
PC
and
PC
but not for
o
PC
and
m
PC
. Theoretical modelling of the low-energy transition in the first excited states of
p
PC
and
PC
upon the rotation of the
o
-carborane cage verified that the above orthogonality plays an important role in the maximisation of ICT-based luminescence. Our findings suggest that the molecular geometry around the
o
-carborane cage is a major factor determining the efficiency of ICT-based radiative decay in
o
-carboranyl-substituted π-conjugated fluorophores.
The distinct difference in solid-state emission efficiency between 1
H
-phenanthro[9,10-
d
]imidazole-
o
-carboranyl luminophores showed that the geometric orientation is a key factor for controlling intramolecular charge transfer-based radiative decay. |
|---|---|
| Bibliography: | 2113081-2113084 p For ESI and crystallographic data in CIF or other electronic format see DOI PC for the and Electronic supplementary information (ESI) available: Multinuclear NMR spectra, X-ray crystallographic data in CIF format. CCDC carboranyl compounds 10.1039/d1qi01405f , m o |
| ISSN: | 2052-1553 |
| DOI: | 10.1039/d1qi01405f |