Altering the Emission Behavior with the Turn of a Thiophene Ring:  The Photophysics of Condensed Ring Systems of Alternating Benzenes and Thiophenes

Abstract

Six aromatic compounds with embedded thiophenes differing in the number of rings (2-5) and thiophene orientation along the long axis of the molecule (syn, anti) were investigated. Photophysical properties, steady-state absorption, fluorescence, phosphorescence, lifetimes, quantum yields, and a comprehensive time-resolved spectroscopic analysis (femtosecond and nanosecond transient absorption spectroscopy) have been studied as a function of molecular structure.

A comprehensive study of the spectral and photophysical properties of arylthiophenes

“…Although the compounds display low fluorescence yields, they efficiently radiatively deactivate through the lowest triplet state which can be used to improve and tune modern organic conjugated polymers. From the six compounds here investigated, some data is available regarding some photophysical properties of the compounds presenting the simplest structures: benzothiophene [20] and dibenzothiophene [20,21]. However, even in these cases, only a limited amount of data is presented.…”

Heteroacene Synthesis through C−S Cross‐Coupling/5‐endo‐digCyclization

“…However, the HOMO energy levels and consequently the HOMO–LUMO gaps of 1 c and 2 are strongly influenced by the Ph 2 N unit compared to unsubstituted benzo[1,2‐ b :4,5‐ b′ ]dithiophene (DBT) and thieno[2,3‐ f :5,4‐ f′ ]bis[1]benzothiophene (DTBDT) . The HOMO–LUMO gaps are diminished in 1 c and 2 by 0.79 and 0.49 eV respectively compared to the unsubstituted mother compounds (DBT: Δ E opt =3.6 eV, DTBDT: Δ E opt =3.27 eV); the HOMO energy levels are significantly raised by the electron‐rich substituent. The HOMO energy level of unsubstituted DBT was estimated from the oxidation onset in the cyclic voltammogram to be −5.9 eV, which matches very well with the HOMO energy of 1 a .…”

End-capping of conjugated thiophene–benzene aromatic systems

“…The calculated radiative rate constant is in the order of 10 6 s À1 compared to 10 7 s À1 for the parent, nonalkylated molecule, 25 while the nonradiative rate constants (Table 2) are in the order of 10 8 s À1 , similar to the parent, nonalkylated molecule. 25 In summary, we report the preparation, electronic and spectroscopic characterization of two new materials for potential use in organic field-effect transistor applications.…”

“…The fluorescence quantum yield was, in general, found to be very poor and in most cases it was obtained as w0.01 for both 1a and 1b, similar to the nonalkylated parent compound. 25 The radiative rate constant was calculated by the equation. 15 k r ¼ f f =s f where k r is the radiative rate constant, f f is the fluorescence quantum yield, and s f is the fluorescence lifetime, and the nonradiative rate constant is evaluated as 15…”

“…25 In summary, we report the preparation, electronic and spectroscopic characterization of two new materials for potential use in organic field-effect transistor applications.…”