Research Projects

Phosphorescence has long been recognized as a fascinating photophysical phenomenon; however, it has predominantly been observed in heavy metal-based complexes and has demonstrated significant potential in diverse applications, including forensic analysis, security labeling, technologies, optoelectronic lighting, and chemical sensing. However, metal complexes are associated with issues such as toxicity, rarity, and limited availability. Recent studies have revealed that organic molecules can be engineered to exhibit phosphorescence using a variety of innovative strategies, including the incorporation of heteroatoms, hydrogen bonding, crystal engineering, host-guest interactions, and external heavy atom effects. Despite significant advances, organic molecules suffer from potential issues, including: (i) low phosphorescence quantum yields; (ii) the often-unavoidable use of polymer matrices to disperse the molecules for strong phosphorescence; (iii) the processing dependence on hazardous organic solvents. This proposal circumvents above issues by rationally functionalizing chromophores with multiple hydroxy groups, which offer several advantages: (i) they enable strong three-dimensional hydrogen-bonding networks that can completely rigidify the molecular structure, which enhances the radiative transition probability from the triplet state; (ii) the introduced hydrophilic groups are expected to impart water solubility, allowing for aqueous processing; (iii) the presence of heteroatoms (N, O, and S), along with hydrogen bonding, is anticipated to enhance singlet-to-triplet intersystem crossing; and (iv) these molecules are also expected to form well-defined self-assembled structures, which will be explored as potential room-temperature phosphorescence (RTP) waveguides. To the best of our knowledge, there were no significant literature reports on chromophores with multiple hydroxy groups as a strategy for efficient RTP and their optical waveguiding characteristics. Therefore, these materials set a new avenue in the field of optoelectronic and photonic applications. We have rationally designed a series of target molecules (T1–T8) incorporating multiple heteroatoms, which enable the singlet excited state (S₁) to exhibit a hybridized local and charge-transfer character. This leads to an orbital distribution distinct from that of the triplet states (T), thereby facilitating an efficient singlet-to-triplet intersystem crossing (ISC) process. Abundant appended hydroxy groups form a strong 3D-bonding network that effectively suppresses molecular vibrations, thereby facilitating efficient RTP. Preliminary DFT/TD-DFT calculations at the PBE0/6-31G(d,p) level of theory revealed that the designed target molecules have high-lying triplets that are close in energy to the singlet excited state, and thus better spin–orbit coupling matrix elements and high-yielding triplets are expected for strong RTP; these preliminary results support the proposed project.