Apart from sensing and imaging, luminogens with aggregation-induced emission (AIE) are also interesting for photosensitizing. The photosensitizing behavior and bacteria-killing performance of a pyridinium-substituted tetraphenylethylene with an alkyne group ( TPE-A-Py+) is reported herein. Interestingly, TPE-A-Py+ exhibits higher photosensitizing efficiency than TPE-Py+ (without alkyne group) when I− was used as a counteranion. This is well explained by the fact that the Δ ΕST between the excited singlet state ( S1) and triplet state ( T1) was lower for TPE-A-Py+ than for TPE-Py+, according to theoretical calculations. Moreover, replacement of I− with other anions (PF6−, N(SO2CF3)2− and BPh4−) led to a decrease of photosensitizing efficiency for TPE-A-Py+. Notably, TPE-A-Py+ could be used as an efficient photosensitizer to photo-inactivate ampicillin-resistant (ampr) E. coli at low concentration under white-light irradiation very quickly. [ABSTRACT FROM AUTHOR]