Intramolecular Energy Transfer in Dithienogermole Derivatives

Abstract

Dithienogermole (DTG) has been applied asa useful building unit of optical/semiconducting materials for organic optoelectronic devicesb ecause of its extended conjugation, high chemical stability,a nd good emissive properties. Although DTG has two substituents on the Ge atom, the substituents have been limitedt os imple alkyl and aryl groups in previousw ork. In this work, to further uncover the new functionalities of this useful building unit, various pconjugated groups were introduced on Ge of DTG.Itwas expected that the introduction of p-conjugated groups would give rise to efficient energy transfer between the substituents andt he DTG core, which are in proximity and linked by aG ea tom. The thus-prepared DTG compounds with fluo-rene, terthiophene, and pyrene units on Ge possessed wellseparatedf rontier orbitals on the substituents and the DTG core, as provedb yt he absorption spectra and DFT calculations. The substituted DTG derivativess howedc leare mission only from the energya cceptor even though the energy donor was photoexcited. This indicated theh ighly efficient energy transfer in these compounds. We also prepared more p-extended compound DTGFl2-Ph with phenyl groups on the DTG thiophener ings. DTGFl2-Ph showeds trong emission in the visible region with efficient energy transfer properties. These resultsc learly indicate the potential application of the present DTG system as optical functionalmaterials.[a] Dr.Y .A dachi, T.Scheme1.Synthetic route to DTG structure.Scheme2.Structuralmoleculardesign of prior work and the present study.

Optical Characteristics of Hybrid Macrocycles with Dithienogermole and Tricoordinate Boron Units

“…This is presumably due to Fçrster resonance energy transfer (FRET) [9] from the DTG structures to the di([2,2'bithiophen]-5-yl)boranem oieties, as observed in previously re-ported aryl-substituted DTG derivatives. [7] Similar FRET from the DTG moieties to the di([2,2'-bithiophen]-5-yl)boranem oieties was also found in the fluorescence spectra for cTh-2 (Figure S7 in the SupportingI nformation). Attempts to estimate FRET efficiencies were unsuccessful because the DTG absorption highly overlappedw ith the absorption of the macrocyclic backbone.…”

“…However, the fluorescence from the DTG moieties was nearly absent if cTh‐1 was excited at 349 nm (Figure S7 in the Supporting Information). This is presumably due to Förster resonance energy transfer (FRET) [9] from the DTG structures to the di([2,2′‐bithiophen]‐5‐yl)borane moieties, as observed in previously reported aryl‐substituted DTG derivatives [7] . Similar FRET from the DTG moieties to the di([2,2′‐bithiophen]‐5‐yl)borane moieties was also found in the fluorescence spectra for cTh‐2 (Figure S7 in the Supporting Information).…”

“… [1d] The extended conjugation in DTG because of high planarity leads to the use of DTG derivatives as electron‐donating groups. In addition, effective energy and electron transfer occurs between the DTG unit and the aryl substituents on the germanium atom [7] …”

“…In addition, effective energy and electront ransfer occursb etween the DTG unit and the aryl substituents on the germanium atom. [7] Expecting that the combination of FBDT and DTG would providen ew element-hybrid conjugated materials, we recently prepared ap olymer, the backbone of which was composed of FBDT and DTG units (pDTGFBDT;F igure 1). [5b] TheF BDT and DTG units were connected by the a positions of the thiophene rings of each unit, resulting in an extended conjugation through the boronporbital and the conjugated thiophene p orbitals in the backbone.…”

Dithienothiophenes at Work: Access to Mechanosensitive Fluorescent Probes, Chalcogen-Bonding Catalysis, and Beyond

“…Push–pull systems 78 with strong tetracyanoethylene (TCNE) acceptors provide access to solvatochromism and environmental sensitivity. , Ethanol vapor can be sensed with the naked eye from the color change from purple (541 nm) to violet (579 nm) of vapor-deposited films. Moving from siloles 79 to germole bridges 80 , LUMO levels increase, but spectroscopic properties do not change much, including strong fluorescence. Dithieno­stannols 81 are poorly fluorescent in solution (<1%) and amorphous powders (9%) but emit bright blue light from single crystals (56%) …”