Two corroles 10-(4-nitrophenyl)-5,15-bis(pentafluorophenyl)corrole and
5,10,15-Tris(pentafluorophenyl)corrole are taken into consideration. The nitrophenyl corrole belongs to the A 2 B type whereas the pentafluoride to the type A 3 .
The results performed with the quantum chemical calculations indicate their
absolutely different behavior. The nitrophenyl corrole is tautomer T1 and pentafluoro corrole—tautomer T2. However, the DFT calculations for both tautomers of
nitrophenyl corrole show that the energy difference between them is very low
(<0.001 eV) in comparison to kT (0.026 eV at 300 K). It means that both tautomers
exist at room temperature while at low temperature the tautomer with lower total
energy (T2) is preferred. Since it is rather difficult to recognize Tautomer T1 from
T2, the Gouterman four-orbital model lets to assign the electronic energies of T1
and T2 and electronic transitions S 1 –S 0 , S 2 –S 0 [54].
Because of such specific photophysicochemical properties, corroles are very
different from those of porphyrins and phthalocyanines and not yet fully understandable. Apart from experimental studies whose results showed unexpected
properties of the corroles (UV-VIS absorption, also with in situ absorption technique, FT-IR spectroscopy, fluorescence emission, fluorescence kinetics), also
computer chemical calculations are very often used as a helpful approach to the
issue of determining the HOMO and LUMO states as well reorganization energy
[55–57]. Moreover, the basic properties allow recognizing the processes of tautomerization, deprotonation, and induced mesomeric effects occurring in corroles
and their influence on singlet and triplet excited states [58–62].
The more and more advanced chemical procedure has opened a gate to receive
many types of new corroles [63, 64]. The significant advantage of corroles is their
quite simple synthesis. Recent developments of chemistry made it possible—
e.g., preparation of trans-A 2 B-corroles [63] and also self-organization of
meso-substituted corroles possessing secondary amide groups methods were
developed [65–67]. Also creation of corrole aggregates is of a great interest [63, 64]
for their applications in the future optoelectronics and in many other fields of science
and technology such as electronics, sensory, medicine, photovoltaic cell models as
well as in modeling of photophysical and photochemical processes occurring in
photosynthesis [68–70].
The infrared spectroscopy is a powerful tool in the investigation of molecular
systems. The key feature is the ability to identify even very small changes in the
molecular structure and/or interaction with the surroundings. Additionally, if we
support the infrared experimental techniques with density functional theory (DFT)
methods using Gaussian [71] or similar software, the assignment of the observed
bands to appropriate normal modes becomes more reliable. Below we will
demonstrate the use of this method for investigations of two free-base corroles as an
example. Despite the significant and still growing number of investigations focused
on the corroles, there is still little known about their basic vibrational properties and
characteristic infrared or Raman bands. The works of Ghosh [72, 73] and
Czernuszewicz [74] are focused on metallocorroles and discussing mainly the
resonance Raman spectra. There are also the DFT studies of iron and germanium
corroles [75] and transition metal corrolazine complexes (corrolazine is a corrole
3 Quantum Dot and Fullerene with Organic Chromophores as …
107
5,10,15-Tris(pentafluorophenyl)corrole are taken into consideration. The nitrophenyl corrole belongs to the A 2 B type whereas the pentafluoride to the type A 3 .
The results performed with the quantum chemical calculations indicate their
absolutely different behavior. The nitrophenyl corrole is tautomer T1 and pentafluoro corrole—tautomer T2. However, the DFT calculations for both tautomers of
nitrophenyl corrole show that the energy difference between them is very low
(<0.001 eV) in comparison to kT (0.026 eV at 300 K). It means that both tautomers
exist at room temperature while at low temperature the tautomer with lower total
energy (T2) is preferred. Since it is rather difficult to recognize Tautomer T1 from
T2, the Gouterman four-orbital model lets to assign the electronic energies of T1
and T2 and electronic transitions S 1 –S 0 , S 2 –S 0 [54].
Because of such specific photophysicochemical properties, corroles are very
different from those of porphyrins and phthalocyanines and not yet fully understandable. Apart from experimental studies whose results showed unexpected
properties of the corroles (UV-VIS absorption, also with in situ absorption technique, FT-IR spectroscopy, fluorescence emission, fluorescence kinetics), also
computer chemical calculations are very often used as a helpful approach to the
issue of determining the HOMO and LUMO states as well reorganization energy
[55–57]. Moreover, the basic properties allow recognizing the processes of tautomerization, deprotonation, and induced mesomeric effects occurring in corroles
and their influence on singlet and triplet excited states [58–62].
The more and more advanced chemical procedure has opened a gate to receive
many types of new corroles [63, 64]. The significant advantage of corroles is their
quite simple synthesis. Recent developments of chemistry made it possible—
e.g., preparation of trans-A 2 B-corroles [63] and also self-organization of
meso-substituted corroles possessing secondary amide groups methods were
developed [65–67]. Also creation of corrole aggregates is of a great interest [63, 64]
for their applications in the future optoelectronics and in many other fields of science
and technology such as electronics, sensory, medicine, photovoltaic cell models as
well as in modeling of photophysical and photochemical processes occurring in
photosynthesis [68–70].
The infrared spectroscopy is a powerful tool in the investigation of molecular
systems. The key feature is the ability to identify even very small changes in the
molecular structure and/or interaction with the surroundings. Additionally, if we
support the infrared experimental techniques with density functional theory (DFT)
methods using Gaussian [71] or similar software, the assignment of the observed
bands to appropriate normal modes becomes more reliable. Below we will
demonstrate the use of this method for investigations of two free-base corroles as an
example. Despite the significant and still growing number of investigations focused
on the corroles, there is still little known about their basic vibrational properties and
characteristic infrared or Raman bands. The works of Ghosh [72, 73] and
Czernuszewicz [74] are focused on metallocorroles and discussing mainly the
resonance Raman spectra. There are also the DFT studies of iron and germanium
corroles [75] and transition metal corrolazine complexes (corrolazine is a corrole
3 Quantum Dot and Fullerene with Organic Chromophores as …
107