After successfully preparing the proposed panel of SiHDs, we proceeded to determine if any of these dyes were candidates for multimodal SWIR imaging. While withthe λabs for SiHD-1 (855 nm, 131 nm red-shift) and Si-HD-2 (850 nm, 110 nm red-shift) did not reach the SWIR window (Figure , S2), a direct comparison to the matching HD analogs provided crucial insight (Table ). We found that installation of the SiMe2 group onto this platform resulted in a λabs shift that exceeds what is typically seen with other dyes (~90 nm). Moreover, we discovered that relative to SiHD-1, the benzo[cd] indolium modification (SiHD-3) further shifted the λabs by an additional 133 nm to 988 nm (Figure ). Having identified a promising lead compound, all subsequent experiments were focused on evaluating SiHD-3 (herein referred to as SWIR-HD).