2025/10/23 by Aarzoo Aarzoo, Ram Kinkar Roy · 1 voice
Chemistry · Engineering · Materials Science · #Luminescence and Fluorescent Materials #Organic Light-Emitting Diodes Research #Photochemistry and Electron Transfer Studies
paper · pdf · doi:10.1021/acsomega.5c05315
openalex created_date 2025/10/23 · openalex publication_date 2025/10/23 · openalex updated_date 2026/06/15
High Resolution Image Download MS PowerPoint Slide The mechanisms behind the fluorescence quenching of the styrene derivative, 4-dimethylamino-2-benzylidene malonic acid dimethyl ester (BIM) in solution are investigated computationally in the present study. Utilizing a penalty-constrained search algorithm of geometry optimization along with spin-flip long-range corrected time-dependent density functional theory (SF-LC-TDDFT), we examined the energetic and structural changes of the BIM molecule at the minimum energy conical intersection (MECI) between S 1 and S 0 states. Our results reveal that the S 1 excited state approaches the MECI through simultaneous rotation of the α-bond and the pyramidalization of the ethylenic C═C bond. Notably, the S 1 –S 0 energy gap at MECIs are 1.83 and 9.26 kJ/mol (nearly degenerate), and the oscillator strength ( f ) values are 0.000008 au, and 0.00003 au, indicating a nonradiative decay in solution state. Quantitatively, the radiative decay rate ( k r ) is found to be 2.44 × 10 6 s –1, whereas the nonradiative rates via MECIs reach 10 11 –10 12 s –1, underscoring the efficiency of internal conversion. The geometry observed at the MECI, which corresponds to a charge-transfer state, strongly indicates that the BIM molecule operates as a twisted intramolecular charge transfer (TICT) system (as evidenced from the response coefficients of the corresponding frontier orbitals), with quenching facilitated by α-torsional rotation. Our findings delineate a powerful approach to molecular design that effectively manipulates the aggregation effects for enhanced optical emission.