FT Raman and DFT Study on a Series of All‐anti Oligothienoacenes End‐Capped with Triisopropylsilyl Groups

Abstract

Herein, we study the pi-conjugational properties of a homologous series of all-anti oligothienoacenes containing four to eight fused thiophene rings by means of FT Raman spectroscopy and DFT calculations. The theoretical analysis of the spectroscopic data provides evidence that selective enhancement of a very limited number of Raman scatterings is related to the occurrence in these oligothienoacenes of strong vibronic coupling between collective nu(C=C) stretching modes in the 1600-1300 cm(-1) region and the HOMO/LUMO frontier orbitals (HOMO=highest occupied molecular orbital; LUMO=lowest unoccupied molecular orbital). The correlation of the Raman spectroscopic data and theoretical results for these all-anti oligothienoacenes with those previously collected for a number of all-syn oligothienohelicenes gives further support to the expectation that cross-conjugation is dominant in heterohelicenes. Fully planar all-anti oligothienoacenes display linear pi conjugation which seemingly does not reach saturation with increasing number of annulated thiophene rings in the oligomeric chain at least up to the octamer.

Neutral and Oxidized Triisopropylsilyl End‐Capped Oligothienoacenes: A Combined Electrochemical, Spectroscopic, and Theoretical Study

“…The fluorescence spectra recorded in MeTHF at 103 K for TIPS‐ T5 ‐TIPS and at 77 K for TIPS‐ T8 ‐TIPS (Figure 5, bottom) also exhibit two resolved vibronic progressions with energy splittings (≈1400 and ≈450 cm −1 ) smaller than those observed for the absorption spectra (≈1525 and ≈480 cm −1 ). These progressions can be assigned on the basis of the vibrational properties calculated for TIPS‐ T n ‐TIPS compounds in their ground state 42. The first progression can be attributed to totally symmetric, collective ν(CC) stretching modes of the oligothienoacene core, as depicted in Figure 6 a for TIPS‐ T8 ‐TIPS.…”

Benzo-thia-fused [n]thienoacenequinodimethanes with small to moderate diradical characters: the role of pro-aromaticity versus anti-aromaticity

“…On heating up to 140 °C, the most noticeable finding is the coalescence of the 1423 cm –1 thieno-quinoidal band and the simultaneous emergence of two new medium bands at 1466/1451 cm –1 . Characteristic Raman bands around 1460 cm –1 have been reported for aromatic thienoacene cores 18 meaning that the clearance of the quinoidal band (1423 cm –1 ) is at the expenses of the rise of aromatic ones (1466/1451 cm –1 ). In addition the pre-existing most intense Raman scatterings around 1350 cm –1 enlarge their separation from low temperature (7 cm –1 ) to high (12 cm –1 ) temperature revealing the transformation between two species, one at low temperature with a less defined aromatic structure (pseudo-aromatic or singlet with incipient diradical structure) and another at high temperatures with more distinguished aromatic feature typical of diradical triplets.…”

Synthesis, Spectroscopy, and Computational Analysis of Photoluminescent Bis(aminophenyl)‐Substituted Thiophene Derivatives

“…Additionally, these types of compounds have been subjected to theoretical studies. These cover, for example, investigations of vibrational (IR and Raman)9 and electrochemical10 properties as well as the treatment of excited states 11. However, in most cases no experimental data was supplied for comparison with the calculated properties.…”