Similar chemical structures, dissimilar triplet quantum yields: a CASPT2 model rationalizing the trend of triplet quantum yields in nitroaromatic systems

S1/S0 accessibility strongly influences the triplet quantum yields of nitronaphthalenes.

Light-harvesting porphyrazines to enable intramolecular singlet fission

Quantitative intramolecular FRET from a porphyrazine to pentacene enhances singlet fission with triplet quantum yields up to 200% ± 20% in benzonitrile.

Studying the intersystem crossing rate and triplet quantum yield of meso-substituted porphyrins by means of pulse train fluorescence technique

Excited state dynamics, particularly intersystem crossing, of a set of meso-substituted porphyrins bearing different electron–donor and acceptor groups was studied by pulse train fluorescence technique. Triplet quantum yield was found to be critically dependent on the nature of meso-substituents in the porphyrin system. Porphyrins with meso methoxyphenyl groups were found to show high triplet quantum yields ([Formula: see text] between 0.70 and 0.81). Moreover, the quantity of methoxyphenyl groups and the substitution pattern directly influence [Formula: see text]. Alternatively, porphyrins attached to nitrophenyl group possess low triplet quantum yield values (~0.3). The observed structure-properties relationships suggest new ways for tuning the optical properties of porphyrins via chemical modification.

Singlet fission in pentacene dimers

Singlet fission (SF) has the potential to supersede the traditional solar energy conversion scheme by means of boosting the photon-to-current conversion efficiencies beyond the 30% Shockley–Queisser limit. Here, we show unambiguous and compelling evidence for unprecedented intramolecular SF within regioisomeric pentacene dimers in room-temperature solutions, with observed triplet quantum yields reaching as high as 156 ± 5%. Whereas previous studies have shown that the collision of a photoexcited chromophore with a ground-state chromophore can give rise to SF, here we demonstrate that the proximity and sufficient coupling through bond or space in pentacene dimers is enough to induce intramolecular SF where two triplets are generated on one molecule.

A comparative photophysicochemical study of mono substituted phthalocyanines grafted onto silica nanoparticles

In this study, we report on the covalent linking of carboxylic acid functionalized silica nanoparticles with zinc phthalocyanine mono-substituted non-peripherally and peripherally with either a 4-amino phenoxy (1, peripheral and 2, non-peripheral) or an amino group (3 peripheral). The grafting is achieved via the formation of an amide bond between the carboxylic acid of the silica nanoparticles and the amino group of the phthalocyanine complexes. The hybrid nanoparticles retained the amorphous nature of silica nanoparticles after conjugation. A slight decrease in fluorescence and a general improvement in triplet quantum yields compared to free Pcs were observed. Triplet lifetimes for 2- SiNPs and 3- SiNPs also improved when compared to the free phthalocyanine. The changes in singlet oxygen quantum yields upon conjugation were minimal.

Tetra and octa(2,6-di-iso-propylphenoxy)-substituted phthalocyanines: a comparative study among their photophysicochemical properties

This work reports on the synthesis of novel metal free, zinc, aluminum, gallium and indium tetra and octa (2,6-di-iso-propylphenoxy)-substituted phthalocyanine derivatives. UV-visible and 1H NMR analyses confirm that a non-planar conformation, adapted by the phenoxy substituents due to steric interaction in both derivative series, perfectly discourage cofacial aggregation. Fluorescence quantum yields vary as a function of the number of substituents on the ring periphery, while the fluorescence lifetimes display no distinct trend. Triplet quantum yields are significantly larger for the tetra 2,6-di-iso-propylphenoxy- substituted derivatives relative to their corresponding octa-substituted species. However there was no overall trend in the triplet lifetime values. For almost all of the phthalocyanine derivatives, singlet oxygen was produced with relatively good quantum yields. This study explores the possibility of fine-tuning their physicochemical properties by simple structural modification.

Desired properties of new phthalocyanines for photodynamic therapy

The manuscript focuses on the properties of phthalocyanines (Pcs) that are required for them to be employed as photosensitizers in applications such as photodynamic therapy (PDT). High triplet-state quantum yields and lifetimes as well as high singlet-oxygen quantum yields are required for a good photosensitizer. In addition, absorption of the photosensitizer in the red region of the electromagnetic spectrum is also required, and this can be achieved by ring expansion, substitution with electron-donating ligands, and change of the central metal among others. Quantum dots (QDs) are efficient accumulators of light energy, and they can transfer this energy to molecules that possess a very efficient ability to generate singlet oxygen through a process called Förster resonance energy transfer (FRET). Thus, there is a decrease in the fluorescence quantum yield of the QDs when in the vicinity of Pcs. Triplet quantum yields of the Pcs increase in the presence of QDs.

Synthesis and photophysical properties of octa-substituted phthalocyaninato oxotitanium(IV) derivatives

The synthesis, spectral and photophysical properties including fluorescence quenching of the following octa-substituted oxotitanium phthalocyanines are reported: 2,3,9,10,16,17,23,24-octaphenoxyphthalocyaninato titanium(IV) oxide, 2,3,9,10,16,17,23,24-[octakis(4-t-butylphenoxyphthalocyaninato)]titanium(IV) oxide, 2,3,9,10,16,17,23,24-{octakis[(4-benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide and 2,3,9,10,16,17,23,24-octaphenylthiophthalocyaninato titanium(IV) oxide. The complexes are characterized by 1 H NMR, IR and UV-vis spectroscopies. Their photophysical properties are presented where moderate fluorescence quantum yields (0.14-0.19) and lifetimes were determined. Varied triplet quantum yields were obtained and the triplet lifetimes (40-100 μs) were short.

Effect of aggregation of a cationic phthalocyanine in micelles and in the presence of human serum albumin

The photophysical properties of tetrakis(1,1-dimethyl-2-trimethylammonium)ethylphthalocyaninato zinc(II) tetraiodide (I) – a water-soluble cationic phthalocyanine – are presented in the presence of human serum albumin (HSA) and in micelles of sodium dodecylsulfate ( SDS ) and hexadecyltrimethylammonium chloride ( CTAC ). Spectrophotometric measurements showed that the surfactants SDS and CTAC induce monomerization of I, although the latter less efficiently than the former. This effect is less pronounced in the presence of HSA. The strength of this effect is evaluated through dimerization constants, which are Kd = (5 ± 1) × 105 m−1 in SDS , (1.5 ± 0.5) × 106 M −1 in CTAC , and (1.8 ± 0.9) × 106 M −1 in HSA. Fluorescence experiments confirm that aggregation of I drops as the concentration of surfactant is raised. Triplet quantum yields also decreased upon aggregation and were Φ T = 0.59, 0.16, and < 0.01 in SDS , CTAC , and HSA, respectively. These results indicate that the affinity of I for the environment is not just due to ionic interactions; hydrophobic interactions play an equally important role.