Abstract
Small robust organic molecules showing solid‐state luminescence are promising candidates for optoelectronic materials. Herein, we investigate a series of diphenylphosphanyl anthracenes [9‐PPh2‐10‐R‐(C14H8)] and their sulfur oxidised analogues. The oxidation causes drastic changes in the molecular structure as the new orientation of the bulky (S)PPh2 substituent induces a strong butterfly bent structure of the anthracene core, which triggers a strong bathochromic shift resulting in a green solid‐state fluorescence. As the emission properties change only slightly upon aggregation the origin of the emission is attributed to a typical monomer fluorescence. The host–guest complexes of [9‐(S)PPh2‐10‐Ethyl‐(C14H8)] with four basic arenes reveal an emission enhancement up to five‐times higher quantum yields compared to the pure host. Less interchromophoric interactions and a restriction of intramolecular motion within the host molecules due to fixation by weak C−H⋅⋅⋅π interactions with the co‐crystallised arene are responsible for that emission enhancement.
Highlights
Organic luminescent solid-state materials have spawned great interest in fundamental research and various applications over the last two decades
The low quantum yields can be explained by a photoinduced electron transfer (PET) from the sulfur lone pairs towards the anthracene psystem, which leads to a strong fluorescence quenching
The two phenyl groups are both located at the same side of the anthracene plane and the bulky substituent induces a strong butterfly bent structure of the anthracene core
Summary
Organic luminescent solid-state materials have spawned great interest in fundamental research and various applications over the last two decades. Type interaction usually follows a bathochromic shift of the emission and extends fluorescence’ lifetimes.[26] Exciplex emission can be obtained by host–guest complexes or supramolecular assemblies.[27] Face-to-face interactions of the host molecule and suitable guests can tune the emission wavelengths and effectiveness via a Charge-Transfer (CT) or exciplex mechanism.[28] Some of these systems show interesting vapochromic behaviour and are potential candidates for chemical sensing of volatile, organic compounds.[6,29] One of the first sensors for toluene based on a host–guest system we reported in 2003.[30] The unusual photophysical properties of a disubstituted diphenyl(thiophosphoranyl) anthracene revealed a reversible intense green emission upon co-crystallisation with toluene and a nearly complete fluorescence quenching when the toluene was removed under reduced pressure.
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