Room temperature phosphorescence from heavy atom free benzophenone boronic ester derivatives
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Bull Mater Sci (2020)43:318 https://doi.org/10.1007/s12034-020-02235-y
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Room temperature phosphorescence from heavy atom free benzophenone boronic ester derivatives SWADHIN GARAIN, SUMAN KUILA, ARNAB SINHABABU and SUBI J GEORGE* New Chemistry Unit and School of Advanced Materials, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064, India *Author for correspondence ([email protected]; [email protected]) MS received 4 January 2020; accepted 17 March 2020 Abstract. Two new boronic ester conjugated benzophenone derivatives are reported, which exhibit visible afterglow phosphorescence under ambient conditions and solution-processable thin films. The carbonyl group and pinacol moiety in the molecular design play a crucial role to achieve good phosphorescence efficiency in air. Keywords.
1.
Phosphorescence; benzophenone; afterglow.
Introduction
Room temperature phosphorescence (RTP) from purely organic chromophores has recently received much attention as a promising alternative to expensive and heavy metalbased inorganic phosphors [1–4]. However, design of such molecules has been a challenging task, as most of the organic phosphors suffer low quantum yields at room temperature due to poor inter-system crossing efficiency and high susceptibility toward vibrational as well as oxygen-mediated triplet quenching [5,6]. As a result, organic phosphors with high quantum yield are obtained only in crystalline state, which minimizes the non-radiative quenching of triplet excitons and oxygen diffusion [7–13]. In this context design of solution-processable RTP phosphors is very important for various applications [14–17] and significant impetus is being given for realizing this under ambient conditions. Recently, amorphous state RTP has been achieved in organic systems by incorporating the organic phosphors either in rigid polymer matrices [18–21] or into cage-like hosts [22,23]. Among various organic RTP phosphors, boronic esterbased derivatives are rarely reported [24–29]. Fukushima and co-workers [26] reported that out-of-plane distortion at the B–C bond of the pinacol moiety helps the mixing of r and p orbitals which would enhance the inter-system crossing (ISC) process to significantly increase the phosphorescence emission. However, most of boronic esterbased RTP designs, suffer from low quantum yield which limits their applications. In addition, simple molecular design is important for the scalable synthesis for various This article is part of the Topical Collection: SAMat Focus Issue.
applications. Hence, in this paper, we report the synthesis of two simple boronic ester appended benzophenone-based solution-processable phosphors (BBE1 and BBE2) with reasonable phosphorescence quantum yield (*7%) under ambient condition. We envisage that, the present design with the carbonyl group [29–35] along with the pinacol moiety would enhance the ISC efficiency.
2. 2.1
Experimental Materials
4-Bromo benzophenone, 4,40 -dibromo benzophenone are obtained
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