The influence of molecular conformation on the photophysics of organic room temperature phosphorescent luminophores. Issue 34 (17th August 2018)

• Record Type: Journal Article
• Authors: Huang, Rongjuan; Ward, Jonathan S.; Kukhta, Nadzeya A.; Avó, João; Gibson, Jamie; Penfold, Thomas; Lima, João C.; Batsanov, Andrei S.; Berberan-Santos, Mário N.; Bryce, Martin R.; Dias, Fernando B.
• Is Part Of: Journal of materials chemistry. Volume 6:Issue 34(2018)
• Page Start: 9238
• Page End: 9247
• Publication Date: 2018-08-17
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c8tc02987c
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Tuning of photophysical properties by conformational control with dual RT phosphorescence in metal-free organic emitters. 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 unsubstitutedDPTZ–DBT molecule exists in both equatorial and axial forms in the ground state, due to the ability ofPTZ 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.