Substituent?controlled aggregate luminescence: Computational unraveling of S ₁ /S ₀ surface crossing

We computationally investigated the molecular aggregation effects on excited state deactivation processes by considering both direct vibrational relaxation and S0/S1 surface crossing, that is, minimum energy conical intersection (MECI). Taking classical AIEgens bis(piperidyl)anthracenes (BPAs) isomers substituted silole derivatives as examples, we show deformation of MECI always occurs at atom with greater hole/electron overlap. Besides, energetic structural changes caused substituent has been investigated. find effective such addition electron-donating groups, which can polarize distribution density molecules, will lead to pyramidalization occurring position simultaneously reduce required reach MECI. And is sterically restricted surrounding molecules in solid phase, remarkably hinders non-radiative decay through crossing. Through quantitative computational assessments fluorescence quantum efficiency for solution phases, elucidate role its dependence substitutions deformation, give rise aggregation-induced emission (AIE) phenomenon 9,10-BPA, aggregation-enhance (AEE) behavior 1,4-BPA, conventional aggregation-caused quenching (ACQ) 1,5-BPA. further verify mechanism siloles, found do not change AIE behavior. Our findings render a general design approach manipulating effect optical emission.