Photophysics of Zinc 2,11,20,29-Tetra-tert-butyl-2,3-Naphthalocyanine: Aggregation-Induced S₂ Emission and Rapid Intersystem Crossing in the Solid State

Abstract

Aggregation can dramatically alter the photophysics of organic chromophores by modulating their electronic properties. Zinc 2,11,20, in thin films emits primarily from its second excited singlet state (S 2 ), while t-Bu-ZnNc in solution obeys the well-known Kasha rule and emits from S 1 . This behavior most likely results from the hindered motion of the t-butyl groups in the rigid, closely packed thin films. This is corroborated by the observation of enhanced S 2 emission in low-temperature glassy solutions. The t-Bu-ZnNc films also show rapid intersystem crossing to form a longlived triplet excited state an order of magnitude faster than in solution due to the enhanced density of triplet states and the concomitant reduced singlet−triplet energy gap between the broadened excited state manifolds in the closely packed solid.

Could the Length of the Alkyl Chain Affect the Photodynamic Activity of 5,10,15,20-Tetrakis(1-alkylpyridinium-4-yl)porphyrins?

“…Overall, the values are indicative of a high production of singlet oxygen, confirming the priority role of the ISC in the decay of the excited PS to the fundamental electronic level. Even if the differences are not significant, a slight tendency for Zn-porphyrins to show a greater Φ Δ is observed; on average, this is in agreement with the results in the literature, where it is reported that the coordination with zinc ion favors the ISC process [ 51 ]. Regarding the pendants, the PSs with the two longest alkyl chains (C8 and C12) show the highest 1 O 2 production in the two series.…”