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The influence of molecular conformation on the photophysics of organic room temperature phosphorescent luminophores.

Huang, Rongjuan and Ward, Jonathan S. and Kukhta, Nadzeya A. and Avó, João and Gibson, Jamie and Penfold, Thomas and Lima, João C. and Batsanov, Andrei S. and Berberan-Santos, Mário N. and Bryce, Martin R. and Dias, Fernando B. (2018) 'The influence of molecular conformation on the photophysics of organic room temperature phosphorescent luminophores.', Journal of materials chemistry C., 10 (34). pp. 9238-9247.

Abstract

A series of novel donor–acceptor–donor (D–A–D) compounds featuring dibenzothiophene (DBT) and phenothiazine (PTZ) units are presented. A different degree of steric hindrance between the donor and acceptor fragments is achieved by the systematic changes of donor substituents (methyl, iso-propyl, tert-butyl groups). This leads to the tuning of photophysical properties by conformational control. The unsubstituted DPTZ–DBT molecule exists in both equatorial and axial forms in the ground state, due to the ability of PTZ to form H-extra and H-intra folded conformers that allow formation of parallel quasi-axial (ax) and perpendicular quasi-equatorial (eq) conformers, respectively. However, the equatorial conformer prevails in the excited state. This leads to strong room temperature phosphorescence (RTP) in the green region with high phosphorescence quantum yield (60 ± 8%). Under the influence of bulky substituents, the alkyl-DPTZ–DBT derivatives change molecular conformation, preventing formation of the excited charge transfer state. Hence, blue, but much weaker, phosphorescence is observed. The less bulky methyl substituent on the donor results in dual RTP (blue and green), apparently violating Kasha's rule imposed by the modulation of the barriers between excited states. The experimental results are supported by DFT calculations in the ground and excited state. Control of conformation with substituents is an effective strategy for tuning the excited state properties of D–A–D molecules for RTP emission.

Item Type:Article
Full text:(VoR) Version of Record
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Full text:(VoR) Version of Record
Available under License - Creative Commons Attribution.
Download PDF
(3253Kb)
Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1039/C8TC02987C
Publisher statement:This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Date accepted:05 August 2018
Date deposited:23 August 2018
Date of first online publication:17 August 2018
Date first made open access:No date available

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