Temperature dependent fluorescence in disordered Frenkel chains: interplay of equilibration and local band-edge level structure

We model the optical dynamics in linear Frenkel exciton systems governed by scattering on static disorder and lattice vibrations, and calculate the temperature dependent fluorescence spectrum and lifetime. The fluorescence Stokes shift shows a nonmonotonic behavior with temperature, which derives from the interplay of the local band-edge level structure and thermal equilibration. The model yields excellent fits to experiments performed on linear dye aggregates.Comment: 4 pages, 3 figure

Free base and protonated form fluorescence of the mixed 5,10,15,20-arylporphyrins

Fluorescence spectra for a series of mixed phenyl-mesityl 5,10,15,20-tetraarylporphyrins – with Mes4, Mes3Ph, Mes2Ph2- trans, Mes2Ph2- cis, MesPh 3 and Ph4 type architecture (Mes – mesityl, Ph – phenyl) – in their free base, mono- and diprotonated form are reported. Substitution of a single mesophenyl group with a sterically more demanding mesityl group is found to be sufficient to provide stabi-lization of the monoprotonated porphyrin species. A decrease in the number of mesityl substituents in the macrocycle leads to a decrease in the fluore scence quantum yield for protonated forms. The pro-gressive replacement of ortho,ortho’-substituted mesityl groups with unhindered phenyls results in the additive pattern of spectral changes for the free base porphyrins, whereas for both protonated species a specific jump at the trans to cis transition is observed, along with a gradual additive pattern before and afterwards. This feature is interpreted as a signature of the transition between the hindered-like and un-hindered-like conformations of the tetrapyrrolic m acrocycles in the protonated forms. These two mo-lecular conformations provide a different interaction of the two one-electron (a1u,eg) and (a2u,eg) configurations, which leads to changes of their contributions into electronic transitions

Spectral manifestation of diacid formation for octalkylporphyrins in fluorescence line narrowing spectra

In this work we recorded highly resolved FLN spectra of diprotonated forms of octamethylporphyrin (H[4]OMP{2+}), their meso-deuterated derivative (H[4]OMP{2}+-d4), octaethylporphyrin (H[4]OEP{2+}) and its derivatives with exchanging of central protons on deuterium atoms (D[4]OMP{2+}, D[4]OMP{2+}-d4 and D[4]OEP{2+}) in solid acid solutions at liquid helium temperature

Spectral manifestation of diacid formation for ostalkylporhyrins in fluorescence line narrowing spectra

Many porphyrins moieties in their natural protein environment are highly distorted from planarity have been observed several years ago. As a result of this interest in the properties of nonplanarity of naturally occurring porphyrins, numerous synthetic model porphyrins have been made which mimic these distortions. The spectroscopic investigations of porphyrins at low temperatures may be very effective for studies of distortions of their planar structure under influence of matrices, different kinds of substitution in structure of porphyrin macrocycle, etc. For molecule of porphine with Mg(ll), Zn(ll) and Pd(U) ions the effect of stabilization of different spectral forms in solid matrices was recently demonstrated in fluorescence spectra

Electroluminescence and optical properties of poly(phenylenevinylene)/J-aggregate composites

Abstract A composite material of poly(phenylenevinylene) (PPV) doped by dye aggregates was prepared. A very efficient and temperature activated energy transfer (ET) from the PPV to the dye aggregates was attributed to F . orster ET accompanied by exciton diffusion. A clear complementary relation between the photoluminescence (PL) and electroluminscence (EL) images was observed for thin (15 nm) PPV-based OLEDs. So-called ''black spots'' in EL become bright ones when the photoluminescence of the same area was excited. This effect was attributed to the presence of an insulating layer between the polymer and aluminium.

Repurposing Poly(3-hexylthiophene) as a Conductivity-Reducing Additive for Polyethylene-Based High-Voltage Insulation

Poly(3-hexylthiophene) (P3HT) is found to be a highly effective conductivity-reducing additive for low-density polyethylene (LDPE), which introduces a new application area to the field of conjugated polymers. Additives that reduce the direct-current (DC) electrical conductivity of an insulation material at high electric fields have gained a lot of research interest because they may facilitate the design of more efficient high-voltage direct-current power cables. An ultralow concentration of regio-regular P3HT of 0.0005 wt% is found to reduce the DC conductivity of LDPE threefold, which translates into the highest efficiency reported for any conductivity-reducing additive to date. The here-established approach, i.e., the use of a conjugated polymer as a mere additive, may boost demand in absolute terms beyond the quantities needed for thin-film electronics, which would turn organic semiconductors from a niche product into commodity chemicals

Free base and protonated form fluorescence of the mixed 5,10,15,20-arylporphyrins

Fluorescence spectra for a series of mixed phenyl-mesityl 5,10,15,20-tetraarylporphyrins – with Mes4, Mes3Ph, Mes2Ph2- trans, Mes2Ph2- cis, MesPh 3 and Ph4 type architecture (Mes – mesityl, Ph – phenyl) – in their free base, mono- and diprotonated form are reported. Substitution of a single mesophenyl group with a sterically more demanding mesityl group is found to be sufficient to provide stabi-lization of the monoprotonated porphyrin species. A decrease in the number of mesityl substituents in the macrocycle leads to a decrease in the fluore scence quantum yield for protonated forms. The pro-gressive replacement of ortho,ortho’-substituted mesityl groups with unhindered phenyls results in the additive pattern of spectral changes for the free base porphyrins, whereas for both protonated species a specific jump at the trans to cis transition is observed, along with a gradual additive pattern before and afterwards. This feature is interpreted as a signature of the transition between the hindered-like and un-hindered-like conformations of the tetrapyrrolic m acrocycles in the protonated forms. These two mo-lecular conformations provide a different interaction of the two one-electron (a1u,eg) and (a2u,eg) configurations, which leads to changes of their contributions into electronic transitions

Spectral manifestation of diacid formation for octalkylporphyrins in fluorescence line narrowing spectra

In this work we recorded highly resolved FLN spectra of diprotonated forms of octamethylporphyrin (H[4]OMP{2+}), their meso-deuterated derivative (H[4]OMP{2}+-d4), octaethylporphyrin (H[4]OEP{2+}) and its derivatives with exchanging of central protons on deuterium atoms (D[4]OMP{2+}, D[4]OMP{2+}-d4 and D[4]OEP{2+}) in solid acid solutions at liquid helium temperature