Multistate Emission via Fuorescence and Room Temperature Phosphorescence in and#960; extended Coumarins and Phenoxazine Quinoline Conjugates

Abstract

Multistate emissive materials have attracted enormous interests in the field of white light-emitting diodes (OLED), sensors, security inks, and bio-imaging. Due to the existence of non-radiative decay channels of the excited states, achieving multi-state emission at ambient conditions is a difficult task. Dual state emission processes that occur via excited-state intramolecular proton transfer (ESIPT), twisted intramolecular charge transfer (TICT) and simultaneous emission from higher excited states are reported in the literature. However, these processes are limited only to decay of singlet excited states. On the other hand, harvesting of triplet states as room-temperature phosphorescence (RTP) at ambient conditions is another bottleneck of purely organic molecules, because they have inefficient spin-orbit coupling due to the involvement of lighter elements. More importantly, the localised nature of the triplet excited states of organic systems are highly sensitive to the molecular vibrations and oxygen. Due to these obstacles, achieving room-temperature phosphorescence in a purely organic system at ambient conditions remains a challenging area of research. In this thesis, we have shown how to achieve multistate emissions via fluorescence and room-temperature phosphorescence in different organic dyes with and/or without heavy halogens. By taking advantage of near orthogonal orientation of the donor and acceptor units we could reduce the energy gap between the lowest singlet and triplet states which is a key to achieve RTP at ambient conditions.