Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

Abstract

A comprehensive study has been undertaken of the electronic spectral and photophysical properties of two oligophenyl (BPH and BPHF) and one oligothienyl (BTF) swivel cruciforms involving measurements of absorption, fluorescence, and phosphorescence spectra, quantum yields of fluorescence (φ F ), phosphorescence (φ Ph ) and triplet formation (φ T ), lifetimes of fluorescence (τ F ) and of the triplet state (τ T ), and quantum yields of singlet oxygen production (φ ∆ ). From these, all radiative k F and radiationless rate constants, k IC and k ISC , have been obtained in solution. The energies of the lowest lying singlet and triplet excited states were also determined at 293 K. Several of the above properties have also been obtained at low temperature and in the solid state (thin films). In general, for the phenyl oligophenyl (BPH) and for the oligothienyl (BTF) compounds, the radiationless decay channels (φ IC + φ ISC ) are the dominant pathway for the excited-state deactivation, whereas with the fluorene based oligophenyl BPHF the radiative route prevails. In contrast to the general rule found for related oligomers (and polymers) where radiative emission from T 1 is absent, with the compounds studied, phosphorescence has been observed for all of the compounds, indicating that this type of functionalization can lead to emissive triplets. Time-resolved fluorescence decays with picosecond resolution revealed multiexponential (bi-and triexponential) decay laws compatible with the existence of more than one species or conformation in the excited state. These results are discussed on the basis of conformational flexibility in the excited state.

Excited-State Planarization as Free Barrierless Motion in a π-Conjugated Terpyridine

“…ISC on the other hand stemming from a purely electronic coupling is less affected by decreasing temperature . Based on these considerations our experimental results can be understood as the balanced effect of strongly temperature, that is, fluctuation-dependent IC, and less temperature-dependent ISC. , …”

“…Following this approach, a barrier height of 36.5 kJ/mol for IC is obtained. The height of this barrier is a good explanation for the high fluorescence quantum yield of about 74%, because nonradiative deactivation directly to the ground state seems to be only a weak effect and the remaining about 26% have a significant contribution of ISC …”

Covalently Scaffolded Inter‐π‐System Orientations in π‐Conjugated Polymers and Small Molecule Models

“…This provides another edifying example of how subtle scaffold adjustments can lead to well-defined bis(p-system) ensembles that allow study of multiple distinct species formed in the course of redox processes. Oligothiophenes linked by simpler attachment strategies include swivel cruciforms, [27][28][29][30] in which the oligothiophene chains are attached directly to one another by a single bond, and simple alkyl linkers have also been employed. As an example, a detailed set of studies with quinquethiophene derivatives linked by one (7b) or two (7c-g) alkyl chains ( Figure 7) will be discussed.…”

Carrier-Collision-Induced Formation of Charged Excitons and Ultrafast Dynamics Fluorescence Spectra

“…31 Furthermore, the fluorescence decay also reveals the possibility of existing in an excited state. 32 exciton is annihilated when it interacts with holes, 33 which raises the question as to what kind of interaction induces the annihilation between these two carriers and what the mechanism of this kind of annihilation is. Thus, our first task is to understand the process of formation of the charged triplet exciton after the hole is injected into a PLED.…”