“…Thus, the results allow us to bracket the triplet energy of PPESO 3 – , and it is within the range 1.96–2.25 eV. This result is in good accord with previous investigations of poly(phenyleneethynylene)s, which have indicated similar values for the triplet energy. , …”
Section: Resultssupporting
confidence: 90%
“…This result is in good accord with previous investigations of poly(phenyleneethynylene)s, which have indicated similar values for the triplet energy. 30,31 ■ CONCLUSION…”
We describe a systematic study of triplet sensitization in a poly(phenyleneethynylene) conjugated polyelectrolyte (CPE) in methanol solution by using a series of three cationic iridium complexes with varying triplet energy. The cationic iridium complexes bind to the anionic CPE by ion-pairing, leading to singlet state quenching of the polymer, and allowing for efficient back-transfer of triplet excitation energy to the polymer. Efficient (amplified quenching) of the polymer's fluorescence is observed for each iridium complex, with Stern-Volmer quenching constants in excess of 10(5) M(-1). Triplet sensitization is confirmed for two of the iridium complexes by monitoring the relative yield of the CPE triplet state by transient absorption spectroscopy. One of the iridium complexes does not sensitize the CPE triplet, and consideration of the energies of the three complexes allows us to bracket the triplet energy of the CPE within the range 1.95-2.26 eV.
“…Thus, the results allow us to bracket the triplet energy of PPESO 3 – , and it is within the range 1.96–2.25 eV. This result is in good accord with previous investigations of poly(phenyleneethynylene)s, which have indicated similar values for the triplet energy. , …”
Section: Resultssupporting
confidence: 90%
“…This result is in good accord with previous investigations of poly(phenyleneethynylene)s, which have indicated similar values for the triplet energy. 30,31 ■ CONCLUSION…”
We describe a systematic study of triplet sensitization in a poly(phenyleneethynylene) conjugated polyelectrolyte (CPE) in methanol solution by using a series of three cationic iridium complexes with varying triplet energy. The cationic iridium complexes bind to the anionic CPE by ion-pairing, leading to singlet state quenching of the polymer, and allowing for efficient back-transfer of triplet excitation energy to the polymer. Efficient (amplified quenching) of the polymer's fluorescence is observed for each iridium complex, with Stern-Volmer quenching constants in excess of 10(5) M(-1). Triplet sensitization is confirmed for two of the iridium complexes by monitoring the relative yield of the CPE triplet state by transient absorption spectroscopy. One of the iridium complexes does not sensitize the CPE triplet, and consideration of the energies of the three complexes allows us to bracket the triplet energy of the CPE within the range 1.95-2.26 eV.
“…However, in the simulation of electronic excitations of small molecules and oligomers, the effort has been devoted to the study of the absorption arising from singlet-singlet excitation, leaving the singlet-triplet excitation less investigated [ 127 , 128 ]. An important reason for this omission is that triplet-state energies are not easy to measure through direct optical absorption due to very low singlet-triplet ( S 0 − T 1 ) absorption coefficient [ 129 ] and low phosphorescence quantum yield [ 121 ] (< 10 −6 ). The major approaches to probe triplet states in conjugated polymers are the charge recombination energy transfer, and singlet-triplet ( T 1 − S 0 or S 1 − T 1 ) intersystem crossing [ 130 , 131 , 132 ].…”
Section: Excitation Energies Of Conjugated Polymersmentioning
With technological advances, light-emitting conjugated oligomers and polymers have become competitive candidates in the commercial market of light-emitting diodes for display and other technologies, due to the ultralow cost, light weight, and flexibility. Prediction of excitation energies of these systems plays a crucial role in the understanding of their optical properties and device design. In this review article, we discuss the calculation of excitation energies with time-dependent density functional theory, which is one of the most successful methods in the investigation of the dynamical response of molecular systems to external perturbation, owing to its high computational efficiency.
“…Newer synthetic strategies based on Sonogashira cross-coupling reaction and its modifications have provided numerous possibilities for the design of rigid molecular systems based on phenylethynyl spacer groups. Such molecular systems possess a well-defined architecture and are widely used in the design of functional molecular materials such as conjugated polymers, − donor−acceptor systems, − sensors, − and self-assembled monolayers on metal surfaces. − The major advantage of using the oligo(phenyleneethynylene) core unit as a bridge for electronic communication may be attributed to the cylindrical symmetry of the acetylene unit which maintains the π-electron conjugation at any degree of rotation. Although a variety of phenylethynyl-based molecular systems have been investigated, most of the photophysical reports are based on unsubstituted 1,4-bis(phenylethynyl)benzene ( 1 in Chart ). − 1 Phenylethynyl-Based Molecular Systems under Investigation…”
The unique photophysical, conformational, and electronic properties of two model phenyleneethynylene-based rigid rod molecular systems, possessing dialkoxy substitutions, are reported in comparison with an unsubstituted system. Twisting of the phenyl rings along the carbon-carbon triple bond is almost frictionless in these systems giving rise to planar as well as several twisted ground-state conformations, and this results in broad structureless absorption in the spectral region of 250-450 nm. In the case of 1,4-bis(phenylethynyl)benzene, a broad absorption band was observed due to the HOMO-LUMO transition, whereas dialkoxy-substituted compounds possess two well-separated bands. Dialkoxy substitution in the 2,5-position of the phenyl ring in phenyleneethynylenes alters its central arene pi-orbitals through the resonance interaction with oxygen lone pairs resulting in similar orbital features for HOMO and HOMO-1/HOMO-2. Electronic transition from the low-lying HOMO-1/HOMO-2 orbital to LUMO results in the high-energy band, and the red-shifted band originates from the HOMO-LUMO transition. The first excited-state transition energies at different dihedral angles, calculated by the TDDFT method, indicate that the orthogonal conformation has the highest excitation energy with an energy difference of 15 kcal/mol higher than the low-lying planar conformation. The emission of these compounds originates preferentially from the more relaxed planar conformation resulting in well-defined vibronic features. The fluorescence spectral profile and lifetimes were found to be independent of excitation wavelengths, confirming the existence of a single emitting species.
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