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Room-Temperature Orange-Red Phosphorescence by Way of Intermolecular Charge Transfer in Single-Component Phenoxazine–Quinoline Conjugates and Chemical Sensing

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journal contribution
posted on 29.08.2018, 00:00 by Indranil Bhattacharjee, Nirmalya Acharya, Saheli Karmakar, Debdas Ray
Achieving red phosphorescence from purely organic system is a challenging feat due to the predominant thermal nonradiative decay pathways of the excited electrons. Here, we design single-component charge-transfer (CT) complexes based on phenoxazine–quinoline conjugates (PQ1PQ3), in which the phenoxazine ring is covalently attached to the quinolinyl fragment via a C–N bond. These conjugates in concentration-dependent absorption studies show a new low-energy CT absorption band along with the parent π–π* band with binding constants of up to 102 M–1 due to self-association via intermolecular CT (I2CT). Steady-state emission and phosphorescence decay transient measurements of all of the conjugates in solutions, thin films, and crystals reveal the signature of I2CT that leads to orange-red phosphorescence (ORP) at ambient conditions. Theoretical calculations show the existence of dimer with stronger I2CT characteristics and reduced energy gap between the lowest singlet (S1) and triplet (T1) states (ΔEST = 0.05–0.14 eV), which is in line with emission measurements. These conjugates are used for solid-state dichloromethane vapor sensors, and PQ3 can be transformed into oxygen sensor. These studies give an insight into the ORP properties and provide a rational strategy for the design of single-component self-CT complexes with ORP feature at ambient conditions.